NAME
systemd.exec - Execution environment configurationSYNOPSIS
service.service, socket.socket, mount.mount, swap.swapDESCRIPTION
Unit configuration files for services, sockets, mount points, and swap devices share a subset of configuration options which define the execution environment of spawned processes. This man page lists the configuration options shared by these four unit types. See systemd.unit(5) for the common options of all unit configuration files, and systemd.service(5), systemd.socket(5), systemd.swap(5), and systemd.mount(5) for more information on the specific unit configuration files. The execution specific configuration options are configured in the [Service], [Socket], [Mount], or [Swap] sections, depending on the unit type. In addition, options which control resources through Linux Control Groups (cgroups) are listed in systemd.resource-control(5). Those options complement options listed here.IMPLICIT DEPENDENCIES
A few execution parameters result in additional, automatic dependencies to be added:•Units with WorkingDirectory=,
RootDirectory=, RootImage=, RuntimeDirectory=,
StateDirectory=, CacheDirectory=, LogsDirectory= or
ConfigurationDirectory= set automatically gain dependencies of type
Requires= and After= on all mount units required to access the
specified paths. This is equivalent to having them listed explicitly in
RequiresMountsFor=.
•Similarly, units with
PrivateTmp= enabled automatically get mount unit dependencies for all
mounts required to access /tmp/ and /var/tmp/. They will also gain an
automatic After= dependency on
systemd-tmpfiles-setup.service(8).
•Units whose standard output or error
output is connected to journal or kmsg (or their combinations
with console output, see below) automatically acquire dependencies of type
After= on systemd-journald.socket.
•Units using LogNamespace= will
automatically gain ordering and requirement dependencies on the two socket
units associated with [email protected] instances.
PATHS
The following settings may be used to change a service's view of the filesystem. Please note that the paths must be absolute and must not contain a ".." path component. ExecSearchPath=Takes a colon separated list of absolute paths
relative to which the executable used by the Exec*= (e.g.
ExecStart=, ExecStop=, etc.) properties can be found.
ExecSearchPath= overrides $PATH if $PATH is not supplied
by the user through Environment=, EnvironmentFile= or
PassEnvironment=. Assigning an empty string removes previous
assignments and setting ExecSearchPath= to a value multiple times will
append to the previous setting.
WorkingDirectory=
Takes a directory path relative to the
service's root directory specified by RootDirectory=, or the special
value "~". Sets the working directory for executed processes. If set
to "~", the home directory of the user specified in User= is
used. If not set, defaults to the root directory when systemd is running as a
system instance and the respective user's home directory if run as user. If
the setting is prefixed with the "-" character, a missing working
directory is not considered fatal. If RootDirectory=/RootImage=
is not set, then WorkingDirectory= is relative to the root of the
system running the service manager. Note that setting this parameter might
result in additional dependencies to be added to the unit (see above).
RootDirectory=
Takes a directory path relative to the host's
root directory (i.e. the root of the system running the service manager). Sets
the root directory for executed processes, with the chroot(2) system
call. If this is used, it must be ensured that the process binary and all its
auxiliary files are available in the chroot() jail. Note that setting
this parameter might result in additional dependencies to be added to the unit
(see above).
The MountAPIVFS= and PrivateUsers= settings are particularly
useful in conjunction with RootDirectory=. For details, see below.
If RootDirectory=/RootImage= are used together with
NotifyAccess= the notification socket is automatically mounted from the
host into the root environment, to ensure the notification interface can work
correctly.
Note that services using RootDirectory=/RootImage= will not be
able to log via the syslog or journal protocols to the host logging
infrastructure, unless the relevant sockets are mounted from the host,
specifically:
Example 1. Mounting logging sockets into root environment
This option is only available for system services, or for services running in
per-user instances of the service manager when PrivateUsers= is
enabled.
RootImage=
BindReadOnlyPaths=/dev/log /run/systemd/journal/socket /run/systemd/journal/stdout
Takes a path to a block device node or regular
file as argument. This call is similar to RootDirectory= however mounts
a file system hierarchy from a block device node or loopback file instead of a
directory. The device node or file system image file needs to contain a file
system without a partition table, or a file system within an MBR/MS-DOS or GPT
partition table with only a single Linux-compatible partition, or a set of
file systems within a GPT partition table that follows the Discoverable
Partitions Specification[1].
When DevicePolicy= is set to "closed" or "strict", or
set to "auto" and DeviceAllow= is set, then this setting adds
/dev/loop-control with rw mode, "block-loop" and
"block-blkext" with rwm mode to DeviceAllow=. See
systemd.resource-control(5) for the details about DevicePolicy=
or DeviceAllow=. Also, see PrivateDevices= below, as it may
change the setting of DevicePolicy=.
Units making use of RootImage= automatically gain an After=
dependency on systemd-udevd.service.
This option is only available for system services and is not supported for
services running in per-user instances of the service manager.
RootImageOptions=
Takes a comma-separated list of mount options
that will be used on disk images specified by RootImage=. Optionally a
partition name can be prefixed, followed by colon, in case the image has
multiple partitions, otherwise partition name "root" is implied.
Options for multiple partitions can be specified in a single line with space
separators. Assigning an empty string removes previous assignments. Duplicated
options are ignored. For a list of valid mount options, please refer to
mount(8).
Valid partition names follow the Discoverable Partitions
Specification[1]: root, usr, home, srv,
esp, xbootldr, tmp, var.
This option is only available for system services and is not supported for
services running in per-user instances of the service manager.
RootHash=
Takes a data integrity (dm-verity) root hash
specified in hexadecimal, or the path to a file containing a root hash in
ASCII hexadecimal format. This option enables data integrity checks using
dm-verity, if the used image contains the appropriate integrity data (see
above) or if RootVerity= is used. The specified hash must match the
root hash of integrity data, and is usually at least 256 bits (and hence 64
formatted hexadecimal characters) long (in case of SHA256 for example). If
this option is not specified, but the image file carries the
"user.verity.roothash" extended file attribute (see
xattr(7)), then the root hash is read from it, also as formatted
hexadecimal characters. If the extended file attribute is not found (or is not
supported by the underlying file system), but a file with the .roothash suffix
is found next to the image file, bearing otherwise the same name (except if
the image has the .raw suffix, in which case the root hash file must not have
it in its name), the root hash is read from it and automatically used, also as
formatted hexadecimal characters.
If the disk image contains a separate /usr/ partition it may also be Verity
protected, in which case the root hash may configured via an extended
attribute "user.verity.usrhash" or a .usrhash file adjacent to the
disk image. There's currently no option to configure the root hash for the
/usr/ file system via the unit file directly.
This option is only available for system services and is not supported for
services running in per-user instances of the service manager.
RootHashSignature=
Takes a PKCS7 signature of the
RootHash= option as a path to a DER-encoded signature file, or as an
ASCII base64 string encoding of a DER-encoded signature prefixed by
"base64:". The dm-verity volume will only be opened if the signature
of the root hash is valid and signed by a public key present in the kernel
keyring. If this option is not specified, but a file with the .roothash.p7s
suffix is found next to the image file, bearing otherwise the same name
(except if the image has the .raw suffix, in which case the signature file
must not have it in its name), the signature is read from it and automatically
used.
If the disk image contains a separate /usr/ partition it may also be Verity
protected, in which case the signature for the root hash may configured via a
.usrhash.p7s file adjacent to the disk image. There's currently no option to
configure the root hash signature for the /usr/ via the unit file directly.
This option is only available for system services and is not supported for
services running in per-user instances of the service manager.
RootVerity=
Takes the path to a data integrity (dm-verity)
file. This option enables data integrity checks using dm-verity, if
RootImage= is used and a root-hash is passed and if the used image
itself does not contains the integrity data. The integrity data must be
matched by the root hash. If this option is not specified, but a file with the
.verity suffix is found next to the image file, bearing otherwise the same
name (except if the image has the .raw suffix, in which case the verity data
file must not have it in its name), the verity data is read from it and
automatically used.
This option is supported only for disk images that contain a single file system,
without an enveloping partition table. Images that contain a GPT partition
table should instead include both root file system and matching Verity data in
the same image, implementing the Discoverable Partitions
Specification[1].
This option is only available for system services and is not supported for
services running in per-user instances of the service manager.
MountAPIVFS=
Takes a boolean argument. If on, a private
mount namespace for the unit's processes is created and the API file systems
/proc/, /sys/, /dev/ and /run/ (as an empty "tmpfs") are mounted
inside of it, unless they are already mounted. Note that this option has no
effect unless used in conjunction with RootDirectory=/RootImage=
as these four mounts are generally mounted in the host anyway, and unless the
root directory is changed, the private mount namespace will be a 1:1 copy of
the host's, and include these four mounts. Note that the /dev/ file system of
the host is bind mounted if this option is used without
PrivateDevices=. To run the service with a private, minimal version of
/dev/, combine this option with PrivateDevices=.
In order to allow propagating mounts at runtime in a safe manner,
/run/systemd/propagate/ on the host will be used to set up new mounts, and
/run/host/incoming/ in the private namespace will be used as an intermediate
step to store them before being moved to the final mount point.
ProtectProc=
Takes one of "noaccess",
"invisible", "ptraceable" or "default" (which it
defaults to). When set, this controls the "hidepid=" mount option of
the "procfs" instance for the unit that controls which directories
with process metainformation (/proc/ PID) are visible and accessible:
when set to "noaccess" the ability to access most of other users'
process metadata in /proc/ is taken away for processes of the service. When
set to "invisible" processes owned by other users are hidden from
/proc/. If "ptraceable" all processes that cannot be
ptrace()'ed by a process are hidden to it. If "default" no
restrictions on /proc/ access or visibility are made. For further details see
The /proc Filesystem[2]. It is generally recommended to run most system
services with this option set to "invisible". This option is
implemented via file system namespacing, and thus cannot be used with services
that shall be able to install mount points in the host file system hierarchy.
Note that the root user is unaffected by this option, so to be effective it
has to be used together with User= or DynamicUser=yes, and also
without the "CAP_SYS_PTRACE" capability, which also allows a process
to bypass this feature. It cannot be used for services that need to access
metainformation about other users' processes. This option implies
MountAPIVFS=.
If the kernel doesn't support per-mount point hidepid= mount options this
setting remains without effect, and the unit's processes will be able to
access and see other process as if the option was not used.
This option is only available for system services and is not supported for
services running in per-user instances of the service manager.
ProcSubset=
Takes one of "all" (the default) and
"pid". If "pid", all files and directories not directly
associated with process management and introspection are made invisible in the
/proc/ file system configured for the unit's processes. This controls the
"subset=" mount option of the "procfs" instance for the
unit. For further details see The /proc Filesystem[2]. Note that Linux
exposes various kernel APIs via /proc/, which are made unavailable with this
setting. Since these APIs are used frequently this option is useful only in a
few, specific cases, and is not suitable for most non-trivial programs.
Much like ProtectProc= above, this is implemented via file system mount
namespacing, and hence the same restrictions apply: it is only available to
system services, it disables mount propagation to the host mount table, and it
implies MountAPIVFS=. Also, like ProtectProc= this setting is
gracefully disabled if the used kernel does not support the
"subset=" mount option of "procfs".
BindPaths=, BindReadOnlyPaths=
Configures unit-specific bind mounts. A bind
mount makes a particular file or directory available at an additional place in
the unit's view of the file system. Any bind mounts created with this option
are specific to the unit, and are not visible in the host's mount table. This
option expects a whitespace separated list of bind mount definitions. Each
definition consists of a colon-separated triple of source path, destination
path and option string, where the latter two are optional. If only a source
path is specified the source and destination is taken to be the same. The
option string may be either "rbind" or "norbind" for
configuring a recursive or non-recursive bind mount. If the destination path
is omitted, the option string must be omitted too. Each bind mount definition
may be prefixed with "-", in which case it will be ignored when its
source path does not exist.
BindPaths= creates regular writable bind mounts (unless the source file
system mount is already marked read-only), while BindReadOnlyPaths=
creates read-only bind mounts. These settings may be used more than once, each
usage appends to the unit's list of bind mounts. If the empty string is
assigned to either of these two options the entire list of bind mounts defined
prior to this is reset. Note that in this case both read-only and regular bind
mounts are reset, regardless which of the two settings is used.
This option is particularly useful when RootDirectory=/RootImage=
is used. In this case the source path refers to a path on the host file
system, while the destination path refers to a path below the root directory
of the unit.
Note that the destination directory must exist or systemd must be able to create
it. Thus, it is not possible to use those options for mount points nested
underneath paths specified in InaccessiblePaths=, or under /home/ and
other protected directories if ProtectHome=yes is specified.
TemporaryFileSystem= with ":ro" or ProtectHome=tmpfs
should be used instead.
MountImages=
This setting is similar to RootImage=
in that it mounts a file system hierarchy from a block device node or loopback
file, but the destination directory can be specified as well as mount options.
This option expects a whitespace separated list of mount definitions. Each
definition consists of a colon-separated tuple of source path and destination
definitions, optionally followed by another colon and a list of mount options.
Mount options may be defined as a single comma-separated list of options, in
which case they will be implicitly applied to the root partition on the image,
or a series of colon-separated tuples of partition name and mount options.
Valid partition names and mount options are the same as for
RootImageOptions= setting described above.
Each mount definition may be prefixed with "-", in which case it will
be ignored when its source path does not exist. The source argument is a path
to a block device node or regular file. If source or destination contain a
":", it needs to be escaped as "\:". The device node or
file system image file needs to follow the same rules as specified for
RootImage=. Any mounts created with this option are specific to the
unit, and are not visible in the host's mount table.
These settings may be used more than once, each usage appends to the unit's list
of mount paths. If the empty string is assigned, the entire list of mount
paths defined prior to this is reset.
Note that the destination directory must exist or systemd must be able to create
it. Thus, it is not possible to use those options for mount points nested
underneath paths specified in InaccessiblePaths=, or under /home/ and
other protected directories if ProtectHome=yes is specified.
When DevicePolicy= is set to "closed" or "strict", or
set to "auto" and DeviceAllow= is set, then this setting adds
/dev/loop-control with rw mode, "block-loop" and
"block-blkext" with rwm mode to DeviceAllow=. See
systemd.resource-control(5) for the details about DevicePolicy=
or DeviceAllow=. Also, see PrivateDevices= below, as it may
change the setting of DevicePolicy=.
This option is only available for system services and is not supported for
services running in per-user instances of the service manager.
ExtensionImages=
This setting is similar to MountImages=
in that it mounts a file system hierarchy from a block device node or loopback
file, but instead of providing a destination path, an overlay will be set up.
This option expects a whitespace separated list of mount definitions. Each
definition consists of a source path, optionally followed by a colon and a
list of mount options.
A read-only OverlayFS will be set up on top of /usr/ and /opt/ hierarchies. The
order in which the images are listed will determine the order in which the
overlay is laid down: images specified first to last will result in overlayfs
layers bottom to top.
Mount options may be defined as a single comma-separated list of options, in
which case they will be implicitly applied to the root partition on the image,
or a series of colon-separated tuples of partition name and mount options.
Valid partition names and mount options are the same as for
RootImageOptions= setting described above.
Each mount definition may be prefixed with "-", in which case it will
be ignored when its source path does not exist. The source argument is a path
to a block device node or regular file. If the source path contains a
":", it needs to be escaped as "\:". The device node or
file system image file needs to follow the same rules as specified for
RootImage=. Any mounts created with this option are specific to the
unit, and are not visible in the host's mount table.
These settings may be used more than once, each usage appends to the unit's list
of image paths. If the empty string is assigned, the entire list of mount
paths defined prior to this is reset.
Each image must carry a /usr/lib/extension-release.d/extension-release.IMAGE
file, with the appropriate metadata which matches
RootImage=/RootDirectory= or the host. See:
os-release(5). To disable the safety check that the extension-release
file name matches the image file name, the
x-systemd.relax-extension-release-check mount option may be appended.
When DevicePolicy= is set to "closed" or "strict", or
set to "auto" and DeviceAllow= is set, then this setting adds
/dev/loop-control with rw mode, "block-loop" and
"block-blkext" with rwm mode to DeviceAllow=. See
systemd.resource-control(5) for the details about DevicePolicy=
or DeviceAllow=. Also, see PrivateDevices= below, as it may
change the setting of DevicePolicy=.
This option is only available for system services and is not supported for
services running in per-user instances of the service manager.
ExtensionDirectories=
This setting is similar to
BindReadOnlyPaths= in that it mounts a file system hierarchy from a
directory, but instead of providing a destination path, an overlay will be set
up. This option expects a whitespace separated list of source directories.
A read-only OverlayFS will be set up on top of /usr/ and /opt/ hierarchies. The
order in which the directories are listed will determine the order in which
the overlay is laid down: directories specified first to last will result in
overlayfs layers bottom to top.
Each directory listed in ExtensionDirectories= may be prefixed with
"-", in which case it will be ignored when its source path does not
exist. Any mounts created with this option are specific to the unit, and are
not visible in the host's mount table.
These settings may be used more than once, each usage appends to the unit's list
of directories paths. If the empty string is assigned, the entire list of
mount paths defined prior to this is reset.
Each directory must contain a
/usr/lib/extension-release.d/extension-release.IMAGE file, with the
appropriate metadata which matches RootImage=/RootDirectory= or
the host. See: os-release(5).
Note that usage from user units requires overlayfs support in unprivileged user
namespaces, which was first introduced in kernel v5.11.
This option is only available for system services, or for services running in
per-user instances of the service manager when PrivateUsers= is
enabled.
USER/GROUP IDENTITY
These options are only available for system services and are not supported for services running in per-user instances of the service manager. User=, Group=Set the UNIX user or group that the processes
are executed as, respectively. Takes a single user or group name, or a numeric
ID as argument. For system services (services run by the system service
manager, i.e. managed by PID 1) and for user services of the root user
(services managed by root's instance of systemd --user), the default is
"root", but User= may be used to specify a different user.
For user services of any other user, switching user identity is not permitted,
hence the only valid setting is the same user the user's service manager is
running as. If no group is set, the default group of the user is used. This
setting does not affect commands whose command line is prefixed with
"+".
Note that this enforces only weak restrictions on the user/group name syntax,
but will generate warnings in many cases where user/group names do not adhere
to the following rules: the specified name should consist only of the
characters a-z, A-Z, 0-9, "_" and "-", except for the
first character which must be one of a-z, A-Z and "_" (i.e. digits
and "-" are not permitted as first character). The user/group name
must have at least one character, and at most 31. These restrictions are made
in order to avoid ambiguities and to ensure user/group names and unit files
remain portable among Linux systems. For further details on the names accepted
and the names warned about see User/Group Name Syntax[3].
When used in conjunction with DynamicUser= the user/group name specified
is dynamically allocated at the time the service is started, and released at
the time the service is stopped — unless it is already allocated
statically (see below). If DynamicUser= is not used the specified user
and group must have been created statically in the user database no later than
the moment the service is started, for example using the sysusers.d(5)
facility, which is applied at boot or package install time. If the user does
not exist by then program invocation will fail.
If the User= setting is used the supplementary group list is initialized
from the specified user's default group list, as defined in the system's user
and group database. Additional groups may be configured through the
SupplementaryGroups= setting (see below).
DynamicUser=
Takes a boolean parameter. If set, a UNIX user
and group pair is allocated dynamically when the unit is started, and released
as soon as it is stopped. The user and group will not be added to /etc/passwd
or /etc/group, but are managed transiently during runtime. The
nss-systemd(8) glibc NSS module provides integration of these dynamic
users/groups into the system's user and group databases. The user and group
name to use may be configured via User= and Group= (see above).
If these options are not used and dynamic user/group allocation is enabled for
a unit, the name of the dynamic user/group is implicitly derived from the unit
name. If the unit name without the type suffix qualifies as valid user name it
is used directly, otherwise a name incorporating a hash of it is used. If a
statically allocated user or group of the configured name already exists, it
is used and no dynamic user/group is allocated. Note that if User= is
specified and the static group with the name exists, then it is required that
the static user with the name already exists. Similarly, if Group= is
specified and the static user with the name exists, then it is required that
the static group with the name already exists. Dynamic users/groups are
allocated from the UID/GID range 61184...65519. It is recommended to avoid
this range for regular system or login users. At any point in time each
UID/GID from this range is only assigned to zero or one dynamically allocated
users/groups in use. However, UID/GIDs are recycled after a unit is
terminated. Care should be taken that any processes running as part of a unit
for which dynamic users/groups are enabled do not leave files or directories
owned by these users/groups around, as a different unit might get the same
UID/GID assigned later on, and thus gain access to these files or directories.
If DynamicUser= is enabled, RemoveIPC= and PrivateTmp=
are implied (and cannot be turned off). This ensures that the lifetime of IPC
objects and temporary files created by the executed processes is bound to the
runtime of the service, and hence the lifetime of the dynamic user/group.
Since /tmp/ and /var/tmp/ are usually the only world-writable directories on a
system this ensures that a unit making use of dynamic user/group allocation
cannot leave files around after unit termination. Furthermore
NoNewPrivileges= and RestrictSUIDSGID= are implicitly enabled
(and cannot be disabled), to ensure that processes invoked cannot take benefit
or create SUID/SGID files or directories. Moreover ProtectSystem=strict
and ProtectHome=read-only are implied, thus prohibiting the service to
write to arbitrary file system locations. In order to allow the service to
write to certain directories, they have to be allow-listed using
ReadWritePaths=, but care must be taken so that UID/GID recycling
doesn't create security issues involving files created by the service. Use
RuntimeDirectory= (see below) in order to assign a writable runtime
directory to a service, owned by the dynamic user/group and removed
automatically when the unit is terminated. Use StateDirectory=,
CacheDirectory= and LogsDirectory= in order to assign a set of
writable directories for specific purposes to the service in a way that they
are protected from vulnerabilities due to UID reuse (see below). If this
option is enabled, care should be taken that the unit's processes do not get
access to directories outside of these explicitly configured and managed ones.
Specifically, do not use BindPaths= and be careful with AF_UNIX
file descriptor passing for directory file descriptors, as this would permit
processes to create files or directories owned by the dynamic user/group that
are not subject to the lifecycle and access guarantees of the service.
Defaults to off.
SupplementaryGroups=
Sets the supplementary Unix groups the
processes are executed as. This takes a space-separated list of group names or
IDs. This option may be specified more than once, in which case all listed
groups are set as supplementary groups. When the empty string is assigned, the
list of supplementary groups is reset, and all assignments prior to this one
will have no effect. In any way, this option does not override, but extends
the list of supplementary groups configured in the system group database for
the user. This does not affect commands prefixed with "+".
PAMName=
Sets the PAM service name to set up a session
as. If set, the executed process will be registered as a PAM session under the
specified service name. This is only useful in conjunction with the
User= setting, and is otherwise ignored. If not set, no PAM session
will be opened for the executed processes. See pam(8) for details.
Note that for each unit making use of this option a PAM session handler process
will be maintained as part of the unit and stays around as long as the unit is
active, to ensure that appropriate actions can be taken when the unit and
hence the PAM session terminates. This process is named "(sd-pam)"
and is an immediate child process of the unit's main process.
Note that when this option is used for a unit it is very likely (depending on
PAM configuration) that the main unit process will be migrated to its own
session scope unit when it is activated. This process will hence be associated
with two units: the unit it was originally started from (and for which
PAMName= was configured), and the session scope unit. Any child
processes of that process will however be associated with the session scope
unit only. This has implications when used in combination with
NotifyAccess= all, as these child processes will not be able to
affect changes in the original unit through notification messages. These
messages will be considered belonging to the session scope unit and not the
original unit. It is hence not recommended to use PAMName= in
combination with NotifyAccess=all.
CAPABILITIES
These options are only available for system services, or for services running in per-user instances of the service manager when PrivateUsers= is enabled. CapabilityBoundingSet=Controls which capabilities to include in the
capability bounding set for the executed process. See capabilities(7)
for details. Takes a whitespace-separated list of capability names, e.g.
CAP_SYS_ADMIN, CAP_DAC_OVERRIDE, CAP_SYS_PTRACE.
Capabilities listed will be included in the bounding set, all others are
removed. If the list of capabilities is prefixed with "~", all but
the listed capabilities will be included, the effect of the assignment
inverted. Note that this option also affects the respective capabilities in
the effective, permitted and inheritable capability sets. If this option is
not used, the capability bounding set is not modified on process execution,
hence no limits on the capabilities of the process are enforced. This option
may appear more than once, in which case the bounding sets are merged by
OR, or by AND if the lines are prefixed with "~" (see
below). If the empty string is assigned to this option, the bounding set is
reset to the empty capability set, and all prior settings have no effect. If
set to "~" (without any further argument), the bounding set is reset
to the full set of available capabilities, also undoing any previous settings.
This does not affect commands prefixed with "+".
Use systemd-analyze(1)'s capability command to retrieve a list of
capabilities defined on the local system.
Example: if a unit has the following,
then CAP_A, CAP_B, and CAP_C are set. If the second line is
prefixed with "~", e.g.,
then, only CAP_A is set.
AmbientCapabilities=
CapabilityBoundingSet=CAP_A CAP_B CapabilityBoundingSet=CAP_B CAP_C
CapabilityBoundingSet=CAP_A CAP_B CapabilityBoundingSet=~CAP_B CAP_C
Controls which capabilities to include in the
ambient capability set for the executed process. Takes a whitespace-separated
list of capability names, e.g. CAP_SYS_ADMIN, CAP_DAC_OVERRIDE,
CAP_SYS_PTRACE. This option may appear more than once, in which case
the ambient capability sets are merged (see the above examples in
CapabilityBoundingSet=). If the list of capabilities is prefixed with
"~", all but the listed capabilities will be included, the effect of
the assignment inverted. If the empty string is assigned to this option, the
ambient capability set is reset to the empty capability set, and all prior
settings have no effect. If set to "~" (without any further
argument), the ambient capability set is reset to the full set of available
capabilities, also undoing any previous settings. Note that adding
capabilities to the ambient capability set adds them to the process's
inherited capability set.
Ambient capability sets are useful if you want to execute a process as a
non-privileged user but still want to give it some capabilities. Note that in
this case option keep-caps is automatically added to SecureBits=
to retain the capabilities over the user change. AmbientCapabilities=
does not affect commands prefixed with "+".
SECURITY
NoNewPrivileges=Takes a boolean argument. If true, ensures
that the service process and all its children can never gain new privileges
through execve() (e.g. via setuid or setgid bits, or filesystem
capabilities). This is the simplest and most effective way to ensure that a
process and its children can never elevate privileges again. Defaults to
false, but certain settings override this and ignore the value of this
setting. This is the case when DynamicUser=, LockPersonality=,
MemoryDenyWriteExecute=, PrivateDevices=, ProtectClock=,
ProtectHostname=, ProtectKernelLogs=,
ProtectKernelModules=, ProtectKernelTunables=,
RestrictAddressFamilies=, RestrictNamespaces=,
RestrictRealtime=, RestrictSUIDSGID=,
SystemCallArchitectures=, SystemCallFilter=, or
SystemCallLog= are specified. Note that even if this setting is
overridden by them, systemctl show shows the original value of this
setting. In case the service will be run in a new mount namespace anyway and
SELinux is disabled, all file systems are mounted with MS_NOSUID flag.
Also see No New Privileges Flag[4].
Note that this setting only has an effect on the unit's processes themselves (or
any processes directly or indirectly forked off them). It has no effect on
processes potentially invoked on request of them through tools such as
at(1p), crontab(1p), systemd-run(1), or arbitrary IPC
services.
SecureBits=
Controls the secure bits set for the executed
process. Takes a space-separated combination of options from the following
list: keep-caps, keep-caps-locked, no-setuid-fixup,
no-setuid-fixup-locked, noroot, and noroot-locked. This
option may appear more than once, in which case the secure bits are ORed. If
the empty string is assigned to this option, the bits are reset to 0. This
does not affect commands prefixed with "+". See
capabilities(7) for details.
MANDATORY ACCESS CONTROL
These options are only available for system services and are not supported for services running in per-user instances of the service manager. SELinuxContext=Set the SELinux security context of the
executed process. If set, this will override the automated domain transition.
However, the policy still needs to authorize the transition. This directive is
ignored if SELinux is disabled. If prefixed by "-", failing to set
the SELinux security context will be ignored, but it's still possible that the
subsequent execve() may fail if the policy doesn't allow the transition
for the non-overridden context. This does not affect commands prefixed with
"+". See setexeccon(3) for details.
AppArmorProfile=
Takes a profile name as argument. The process
executed by the unit will switch to this profile when started. Profiles must
already be loaded in the kernel, or the unit will fail. If prefixed by
"-", all errors will be ignored. This setting has no effect if
AppArmor is not enabled. This setting does not affect commands prefixed with
"+".
SmackProcessLabel=
Takes a SMACK64 security label as
argument. The process executed by the unit will be started under this label
and SMACK will decide whether the process is allowed to run or not, based on
it. The process will continue to run under the label specified here unless the
executable has its own SMACK64EXEC label, in which case the process
will transition to run under that label. When not specified, the label that
systemd is running under is used. This directive is ignored if SMACK is
disabled.
The value may be prefixed by "-", in which case all errors will be
ignored. An empty value may be specified to unset previous assignments. This
does not affect commands prefixed with "+".
PROCESS PROPERTIES
LimitCPU=, LimitFSIZE=, LimitDATA=, LimitSTACK=, LimitCORE=, LimitRSS=, LimitNOFILE=, LimitAS=, LimitNPROC=, LimitMEMLOCK=, LimitLOCKS=, LimitSIGPENDING=, LimitMSGQUEUE=, LimitNICE=, LimitRTPRIO=, LimitRTTIME=Set soft and hard limits on various resources
for executed processes. See setrlimit(2) for details on the process
resource limit concept. Process resource limits may be specified in two
formats: either as single value to set a specific soft and hard limit to the
same value, or as colon-separated pair soft:hard to set both limits
individually (e.g. "LimitAS=4G:16G"). Use the string infinity
to configure no limit on a specific resource. The multiplicative suffixes K,
M, G, T, P and E (to the base 1024) may be used for resource limits measured
in bytes (e.g. "LimitAS=16G"). For the limits referring to time
values, the usual time units ms, s, min, h and so on may be used (see
systemd.time(7) for details). Note that if no time unit is specified
for LimitCPU= the default unit of seconds is implied, while for
LimitRTTIME= the default unit of microseconds is implied. Also, note
that the effective granularity of the limits might influence their
enforcement. For example, time limits specified for LimitCPU= will be
rounded up implicitly to multiples of 1s. For LimitNICE= the value may
be specified in two syntaxes: if prefixed with "+" or "-",
the value is understood as regular Linux nice value in the range -20...19. If
not prefixed like this the value is understood as raw resource limit parameter
in the range 0...40 (with 0 being equivalent to 1).
Note that most process resource limits configured with these options are
per-process, and processes may fork in order to acquire a new set of resources
that are accounted independently of the original process, and may thus escape
limits set. Also note that LimitRSS= is not implemented on Linux, and
setting it has no effect. Often it is advisable to prefer the resource
controls listed in systemd.resource-control(5) over these per-process
limits, as they apply to services as a whole, may be altered dynamically at
runtime, and are generally more expressive. For example, MemoryMax= is
a more powerful (and working) replacement for LimitRSS=.
Note that LimitNPROC= will limit the number of processes from one (real)
UID and not the number of processes started (forked) by the service. Therefore
the limit is cumulative for all processes running under the same UID. Please
also note that the LimitNPROC= will not be enforced if the service is
running as root (and not dropping privileges). Due to these limitations,
TasksMax= (see systemd.resource-control(5)) is typically a
better choice than LimitNPROC=.
Resource limits not configured explicitly for a unit default to the value
configured in the various DefaultLimitCPU=, DefaultLimitFSIZE=,
... options available in systemd-system.conf(5), and – if not
configured there – the kernel or per-user defaults, as defined by the
OS (the latter only for user services, see below).
For system units these resource limits may be chosen freely. When these settings
are configured in a user service (i.e. a service run by the per-user instance
of the service manager) they cannot be used to raise the limits above those
set for the user manager itself when it was first invoked, as the user's
service manager generally lacks the privileges to do so. In user context these
configuration options are hence only useful to lower the limits passed in or
to raise the soft limit to the maximum of the hard limit as configured for the
user. To raise the user's limits further, the available configuration
mechanisms differ between operating systems, but typically require privileges.
In most cases it is possible to configure higher per-user resource limits via
PAM or by setting limits on the system service encapsulating the user's
service manager, i.e. the user's instance of [email protected]. After making such
changes, make sure to restart the user's service manager.
Table 1. Resource limit directives, their equivalent ulimit
shell commands and the unit used
UMask=
Directive | ulimit equivalent | Unit | Notes |
LimitCPU= | ulimit -t | Seconds | - |
LimitFSIZE= | ulimit -f | Bytes | - |
LimitDATA= | ulimit -d | Bytes | Don't use. This limits the allowed address range, not memory use! Defaults to unlimited and should not be lowered. To limit memory use, see MemoryMax= in systemd.resource-control(5). |
LimitSTACK= | ulimit -s | Bytes | - |
LimitCORE= | ulimit -c | Bytes | - |
LimitRSS= | ulimit -m | Bytes | Don't use. No effect on Linux. |
LimitNOFILE= | ulimit -n | Number of File Descriptors | Don't use. Be careful when raising the soft limit above 1024, since select() cannot function with file descriptors above 1023 on Linux. Nowadays, the hard limit defaults to 524288, a very high value compared to historical defaults. Typically applications should increase their soft limit to the hard limit on their own, if they are OK with working with file descriptors above 1023, i.e. do not use select(). Note that file descriptors are nowadays accounted like any other form of memory, thus there should not be any need to lower the hard limit. Use MemoryMax= to control overall service memory use, including file descriptor memory. |
LimitAS= | ulimit -v | Bytes | Don't use. This limits the allowed address range, not memory use! Defaults to unlimited and should not be lowered. To limit memory use, see MemoryMax= in systemd.resource-control(5). |
LimitNPROC= | ulimit -u | Number of Processes | This limit is enforced based on the number of processes belonging to the user. Typically it's better to track processes per service, i.e. use TasksMax=, see systemd.resource-control(5). |
LimitMEMLOCK= | ulimit -l | Bytes | - |
LimitLOCKS= | ulimit -x | Number of Locks | - |
LimitSIGPENDING= | ulimit -i | Number of Queued Signals | - |
LimitMSGQUEUE= | ulimit -q | Bytes | - |
LimitNICE= | ulimit -e | Nice Level | - |
LimitRTPRIO= | ulimit -r | Realtime Priority | - |
LimitRTTIME= | ulimit -R | Microseconds | - |
Controls the file mode creation mask. Takes an
access mode in octal notation. See umask(2) for details. Defaults to
0022 for system units. For user units the default value is inherited from the
per-user service manager (whose default is in turn inherited from the system
service manager, and thus typically also is 0022 — unless overridden by
a PAM module). In order to change the per-user mask for all user services,
consider setting the UMask= setting of the user's [email protected] system
service instance. The per-user umask may also be set via the umask
field of a user's JSON User Record[5] (for users managed by
systemd-homed.service(8) this field may be controlled via homectl
--umask=). It may also be set via a PAM module, such as
pam_umask(8).
CoredumpFilter=
Controls which types of memory mappings will
be saved if the process dumps core (using the /proc/
pid/coredump_filter file). Takes a whitespace-separated combination of
mapping type names or numbers (with the default base 16). Mapping type names
are private-anonymous, shared-anonymous,
private-file-backed, shared-file-backed, elf-headers,
private-huge, shared-huge, private-dax,
shared-dax, and the special values all (all types) and
default (the kernel default of " private-anonymous
shared-anonymous elf-headers private-huge"). See
core(5) for the meaning of the mapping types. When specified multiple
times, all specified masks are ORed. When not set, or if the empty value is
assigned, the inherited value is not changed.
Example 2. Add DAX pages to the dump filter
KeyringMode=
CoredumpFilter=default private-dax shared-dax
Controls how the kernel session keyring is set
up for the service (see session-keyring(7) for details on the session
keyring). Takes one of inherit, private, shared. If set
to inherit no special keyring setup is done, and the kernel's default
behaviour is applied. If private is used a new session keyring is
allocated when a service process is invoked, and it is not linked up with any
user keyring. This is the recommended setting for system services, as this
ensures that multiple services running under the same system user ID (in
particular the root user) do not share their key material among each other. If
shared is used a new session keyring is allocated as for
private, but the user keyring of the user configured with User=
is linked into it, so that keys assigned to the user may be requested by the
unit's processes. In this modes multiple units running processes under the
same user ID may share key material. Unless inherit is selected the
unique invocation ID for the unit (see below) is added as a protected key by
the name "invocation_id" to the newly created session keyring.
Defaults to private for services of the system service manager and to
inherit for non-service units and for services of the user service
manager.
OOMScoreAdjust=
Sets the adjustment value for the Linux
kernel's Out-Of-Memory (OOM) killer score for executed processes. Takes an
integer between -1000 (to disable OOM killing of processes of this unit) and
1000 (to make killing of processes of this unit under memory pressure very
likely). See The /proc Filesystem[6] for details. If not specified
defaults to the OOM score adjustment level of the service manager itself,
which is normally at 0.
Use the OOMPolicy= setting of service units to configure how the service
manager shall react to the kernel OOM killer or systemd-oomd
terminating a process of the service. See systemd.service(5) for
details.
TimerSlackNSec=
Sets the timer slack in nanoseconds for the
executed processes. The timer slack controls the accuracy of wake-ups
triggered by timers. See prctl(2) for more information. Note that in
contrast to most other time span definitions this parameter takes an integer
value in nano-seconds if no unit is specified. The usual time units are
understood too.
Personality=
Controls which kernel architecture
uname(2) shall report, when invoked by unit processes. Takes one of the
architecture identifiers x86, x86-64, ppc, ppc-le,
ppc64, ppc64-le, s390 or s390x. Which personality
architectures are supported depends on the system architecture. Usually the
64bit versions of the various system architectures support their immediate
32bit personality architecture counterpart, but no others. For example,
x86-64 systems support the x86-64 and x86 personalities
but no others. The personality feature is useful when running 32-bit services
on a 64-bit host system. If not specified, the personality is left unmodified
and thus reflects the personality of the host system's kernel.
IgnoreSIGPIPE=
Takes a boolean argument. If true,
SIGPIPE is ignored in the executed process. Defaults to true since
SIGPIPE is generally only useful in shell pipelines.
SCHEDULING
Nice=Sets the default nice level (scheduling
priority) for executed processes. Takes an integer between -20 (highest
priority) and 19 (lowest priority). In case of resource contention, smaller
values mean more resources will be made available to the unit's processes,
larger values mean less resources will be made available. See
setpriority(2) for details.
CPUSchedulingPolicy=
Sets the CPU scheduling policy for executed
processes. Takes one of other, batch, idle, fifo
or rr. See sched_setscheduler(2) for details.
CPUSchedulingPriority=
Sets the CPU scheduling priority for executed
processes. The available priority range depends on the selected CPU scheduling
policy (see above). For real-time scheduling policies an integer between 1
(lowest priority) and 99 (highest priority) can be used. In case of CPU
resource contention, smaller values mean less CPU time is made available to
the service, larger values mean more. See sched_setscheduler(2) for
details.
CPUSchedulingResetOnFork=
Takes a boolean argument. If true, elevated
CPU scheduling priorities and policies will be reset when the executed
processes call fork(2), and can hence not leak into child processes.
See sched_setscheduler(2) for details. Defaults to false.
CPUAffinity=
Controls the CPU affinity of the executed
processes. Takes a list of CPU indices or ranges separated by either
whitespace or commas. Alternatively, takes a special "numa" value in
which case systemd automatically derives allowed CPU range based on the value
of NUMAMask= option. CPU ranges are specified by the lower and upper
CPU indices separated by a dash. This option may be specified more than once,
in which case the specified CPU affinity masks are merged. If the empty string
is assigned, the mask is reset, all assignments prior to this will have no
effect. See sched_setaffinity(2) for details.
NUMAPolicy=
Controls the NUMA memory policy of the
executed processes. Takes a policy type, one of: default,
preferred, bind, interleave and local. A list of
NUMA nodes that should be associated with the policy must be specified in
NUMAMask=. For more details on each policy please see,
set_mempolicy(2). For overall overview of NUMA support in Linux see,
numa(7).
NUMAMask=
Controls the NUMA node list which will be
applied alongside with selected NUMA policy. Takes a list of NUMA nodes and
has the same syntax as a list of CPUs for CPUAffinity= option or
special "all" value which will include all available NUMA nodes in
the mask. Note that the list of NUMA nodes is not required for default
and local policies and for preferred policy we expect a single
NUMA node.
IOSchedulingClass=
Sets the I/O scheduling class for executed
processes. Takes one of the strings realtime, best-effort or
idle. The kernel's default scheduling class is best-effort at a
priority of 4. If the empty string is assigned to this option, all prior
assignments to both IOSchedulingClass= and IOSchedulingPriority=
have no effect. See ioprio_set(2) for details.
IOSchedulingPriority=
Sets the I/O scheduling priority for executed
processes. Takes an integer between 0 (highest priority) and 7 (lowest
priority). In case of I/O contention, smaller values mean more I/O bandwidth
is made available to the unit's processes, larger values mean less bandwidth.
The available priorities depend on the selected I/O scheduling class (see
above). If the empty string is assigned to this option, all prior assignments
to both IOSchedulingClass= and IOSchedulingPriority= have no
effect. For the kernel's default scheduling class ( best-effort) this
defaults to 4. See ioprio_set(2) for details.
SANDBOXING
The following sandboxing options are an effective way to limit the exposure of the system towards the unit's processes. It is recommended to turn on as many of these options for each unit as is possible without negatively affecting the process' ability to operate. Note that many of these sandboxing features are gracefully turned off on systems where the underlying security mechanism is not available. For example, ProtectSystem= has no effect if the kernel is built without file system namespacing or if the service manager runs in a container manager that makes file system namespacing unavailable to its payload. Similarly, RestrictRealtime= has no effect on systems that lack support for SECCOMP system call filtering, or in containers where support for this is turned off. Also note that some sandboxing functionality is generally not available in user services (i.e. services run by the per-user service manager). Specifically, the various settings requiring file system namespacing support (such as ProtectSystem=) are not available, as the underlying kernel functionality is only accessible to privileged processes. However, most namespacing settings, that will not work on their own in user services, will work when used in conjunction with PrivateUsers=true. Note that the various options that turn directories read-only (such as ProtectSystem=, ReadOnlyPaths=, ...) do not affect the ability for programs to connect to and communicate with AF_UNIX sockets in these directores. These options cannot be used to lock down access to IPC services hence. ProtectSystem=Takes a boolean argument or the special values
"full" or "strict". If true, mounts the /usr/ and the boot
loader directories (/boot and /efi) read-only for processes invoked by this
unit. If set to "full", the /etc/ directory is mounted read-only,
too. If set to "strict" the entire file system hierarchy is mounted
read-only, except for the API file system subtrees /dev/, /proc/ and /sys/
(protect these directories using PrivateDevices=,
ProtectKernelTunables=, ProtectControlGroups=). This setting
ensures that any modification of the vendor-supplied operating system (and
optionally its configuration, and local mounts) is prohibited for the service.
It is recommended to enable this setting for all long-running services, unless
they are involved with system updates or need to modify the operating system
in other ways. If this option is used, ReadWritePaths= may be used to
exclude specific directories from being made read-only. Similar,
StateDirectory=, LogsDirectory=, ... and related directory
settings (see below) also exclude the specific directories from the effect of
ProtectSystem=. This setting is implied if DynamicUser= is set.
This setting cannot ensure protection in all cases. In general it has the same
limitations as ReadOnlyPaths=, see below. Defaults to off.
ProtectHome=
Takes a boolean argument or the special values
"read-only" or "tmpfs". If true, the directories /home/,
/root, and /run/user are made inaccessible and empty for processes invoked by
this unit. If set to "read-only", the three directories are made
read-only instead. If set to "tmpfs", temporary file systems are
mounted on the three directories in read-only mode. The value
"tmpfs" is useful to hide home directories not relevant to the
processes invoked by the unit, while still allowing necessary directories to
be made visible when listed in BindPaths= or BindReadOnlyPaths=.
Setting this to "yes" is mostly equivalent to setting the three
directories in InaccessiblePaths=. Similarly, "read-only" is
mostly equivalent to ReadOnlyPaths=, and "tmpfs" is mostly
equivalent to TemporaryFileSystem= with ":ro".
It is recommended to enable this setting for all long-running services (in
particular network-facing ones), to ensure they cannot get access to private
user data, unless the services actually require access to the user's private
data. This setting is implied if DynamicUser= is set. This setting
cannot ensure protection in all cases. In general it has the same limitations
as ReadOnlyPaths=, see below.
This option is only available for system services, or for services running in
per-user instances of the service manager when PrivateUsers= is
enabled.
RuntimeDirectory=, StateDirectory=, CacheDirectory=,
LogsDirectory=, ConfigurationDirectory=
These options take a whitespace-separated list
of directory names. The specified directory names must be relative, and may
not include "..". If set, when the unit is started, one or more
directories by the specified names will be created (including their parents)
below the locations defined in the following table. Also, the corresponding
environment variable will be defined with the full paths of the directories.
If multiple directories are set, then in the environment variable the paths
are concatenated with colon (":").
Table 2. Automatic directory creation and environment
variables
In case of
RuntimeDirectory= the innermost subdirectories are removed when the unit
is stopped. It is possible to preserve the specified directories in this case
if RuntimeDirectoryPreserve= is configured to restart or
yes (see below). The directories specified with StateDirectory=,
CacheDirectory=, LogsDirectory=, ConfigurationDirectory=
are not removed when the unit is stopped.
Except in case of ConfigurationDirectory=, the innermost specified
directories will be owned by the user and group specified in User= and
Group=. If the specified directories already exist and their owning
user or group do not match the configured ones, all files and directories
below the specified directories as well as the directories themselves will
have their file ownership recursively changed to match what is configured. As
an optimization, if the specified directories are already owned by the right
user and group, files and directories below of them are left as-is, even if
they do not match what is requested. The innermost specified directories will
have their access mode adjusted to the what is specified in
RuntimeDirectoryMode=, StateDirectoryMode=,
CacheDirectoryMode=, LogsDirectoryMode= and
ConfigurationDirectoryMode=.
These options imply BindPaths= for the specified paths. When combined
with RootDirectory= or RootImage= these paths always reside on
the host and are mounted from there into the unit's file system namespace.
If DynamicUser= is used, the logic for CacheDirectory=,
LogsDirectory= and StateDirectory= is slightly altered: the
directories are created below /var/cache/private, /var/log/private and
/var/lib/private, respectively, which are host directories made inaccessible
to unprivileged users, which ensures that access to these directories cannot
be gained through dynamic user ID recycling. Symbolic links are created to
hide this difference in behaviour. Both from perspective of the host and from
inside the unit, the relevant directories hence always appear directly below
/var/cache, /var/log and /var/lib.
Use RuntimeDirectory= to manage one or more runtime directories for the
unit and bind their lifetime to the daemon runtime. This is particularly
useful for unprivileged daemons that cannot create runtime directories in
/run/ due to lack of privileges, and to make sure the runtime directory is
cleaned up automatically after use. For runtime directories that require more
complex or different configuration or lifetime guarantees, please consider
using tmpfiles.d(5).
RuntimeDirectory=, StateDirectory=, CacheDirectory= and
LogsDirectory= optionally support a second parameter, separated by
":". The second parameter will be interpreted as a destination path
that will be created as a symlink to the directory. The symlinks will be
created after any BindPaths= or TemporaryFileSystem= options
have been set up, to make ephemeral symlinking possible. The same source can
have multiple symlinks, by using the same first parameter, but a different
second parameter.
The directories defined by these options are always created under the standard
paths used by systemd (/var/, /run/, /etc/, ...). If the service needs
directories in a different location, a different mechanism has to be used to
create them.
tmpfiles.d(5) provides functionality that overlaps with these options.
Using these options is recommended, because the lifetime of the directories is
tied directly to the lifetime of the unit, and it is not necessary to ensure
that the tmpfiles.d configuration is executed before the unit is started.
To remove any of the directories created by these settings, use the systemctl
clean ... command on the relevant units, see systemctl(1) for
details.
Example: if a system service unit has the following,
the service manager creates /run/foo (if it does not exist), /run/foo/bar, and
/run/baz. The directories /run/foo/bar and /run/baz except /run/foo are owned
by the user and group specified in User= and Group=, and removed
when the service is stopped.
Example: if a system service unit has the following,
then the environment variable "RUNTIME_DIRECTORY" is set with
"/run/foo/bar", and "STATE_DIRECTORY" is set with
"/var/lib/aaa/bbb:/var/lib/ccc".
Example: if a system service unit has the following,
the service manager creates /run/foo (if it does not exist), and /run/bar plus
/run/baz as symlinks to /run/foo.
RuntimeDirectoryMode=, StateDirectoryMode=,
CacheDirectoryMode=, LogsDirectoryMode=,
ConfigurationDirectoryMode=
Directory | Below path for system units | Below path for user units | Environment variable set |
RuntimeDirectory= | /run/ | $XDG_RUNTIME_DIR | $RUNTIME_DIRECTORY |
StateDirectory= | /var/lib/ | $XDG_CONFIG_HOME | $STATE_DIRECTORY |
CacheDirectory= | /var/cache/ | $XDG_CACHE_HOME | $CACHE_DIRECTORY |
LogsDirectory= | /var/log/ | $XDG_CONFIG_HOME/log/ | $LOGS_DIRECTORY |
ConfigurationDirectory= | /etc/ | $XDG_CONFIG_HOME | $CONFIGURATION_DIRECTORY |
RuntimeDirectory=foo/bar baz
RuntimeDirectory=foo/bar StateDirectory=aaa/bbb ccc
RuntimeDirectory=foo:bar foo:baz
Specifies the access mode of the directories
specified in RuntimeDirectory=, StateDirectory=,
CacheDirectory=, LogsDirectory=, or
ConfigurationDirectory=, respectively, as an octal number. Defaults to
0755. See "Permissions" in path_resolution(7) for a
discussion of the meaning of permission bits.
RuntimeDirectoryPreserve=
Takes a boolean argument or restart. If
set to no (the default), the directories specified in
RuntimeDirectory= are always removed when the service stops. If set to
restart the directories are preserved when the service is both
automatically and manually restarted. Here, the automatic restart means the
operation specified in Restart=, and manual restart means the one
triggered by systemctl restart foo.service. If set to yes, then
the directories are not removed when the service is stopped. Note that since
the runtime directory /run/ is a mount point of "tmpfs", then for
system services the directories specified in RuntimeDirectory= are
removed when the system is rebooted.
TimeoutCleanSec=
Configures a timeout on the clean-up operation
requested through systemctl clean ..., see systemctl(1) for
details. Takes the usual time values and defaults to infinity, i.e. by
default no timeout is applied. If a timeout is configured the clean operation
will be aborted forcibly when the timeout is reached, potentially leaving
resources on disk.
ReadWritePaths=, ReadOnlyPaths=, InaccessiblePaths=,
ExecPaths=, NoExecPaths=
Sets up a new file system namespace for
executed processes. These options may be used to limit access a process has to
the file system. Each setting takes a space-separated list of paths relative
to the host's root directory (i.e. the system running the service manager).
Note that if paths contain symlinks, they are resolved relative to the root
directory set with RootDirectory=/RootImage=.
Paths listed in ReadWritePaths= are accessible from within the namespace
with the same access modes as from outside of it. Paths listed in
ReadOnlyPaths= are accessible for reading only, writing will be refused
even if the usual file access controls would permit this. Nest
ReadWritePaths= inside of ReadOnlyPaths= in order to provide
writable subdirectories within read-only directories. Use
ReadWritePaths= in order to allow-list specific paths for write access
if ProtectSystem=strict is used. Note that ReadWritePaths=
cannot be used to gain write access to a file system whose superblock is
mounted read-only. On Linux, for each mount point write access is granted only
if the mount point itself and the file system superblock backing it are
not marked read-only. ReadWritePaths= only controls the former, not the
latter, hence a read-only file system superblock remains protected.
Paths listed in InaccessiblePaths= will be made inaccessible for
processes inside the namespace along with everything below them in the file
system hierarchy. This may be more restrictive than desired, because it is not
possible to nest ReadWritePaths=, ReadOnlyPaths=,
BindPaths=, or BindReadOnlyPaths= inside it. For a more flexible
option, see TemporaryFileSystem=.
Content in paths listed in NoExecPaths= are not executable even if the
usual file access controls would permit this. Nest ExecPaths= inside of
NoExecPaths= in order to provide executable content within
non-executable directories.
Non-directory paths may be specified as well. These options may be specified
more than once, in which case all paths listed will have limited access from
within the namespace. If the empty string is assigned to this option, the
specific list is reset, and all prior assignments have no effect.
Paths in ReadWritePaths=, ReadOnlyPaths=,
InaccessiblePaths=, ExecPaths= and NoExecPaths= may be
prefixed with "-", in which case they will be ignored when they do
not exist. If prefixed with "+" the paths are taken relative to the
root directory of the unit, as configured with
RootDirectory=/RootImage=, instead of relative to the root
directory of the host (see above). When combining "-" and
"+" on the same path make sure to specify "-" first, and
"+" second.
Note that these settings will disconnect propagation of mounts from the unit's
processes to the host. This means that this setting may not be used for
services which shall be able to install mount points in the main mount
namespace. For ReadWritePaths= and ReadOnlyPaths=, propagation
in the other direction is not affected, i.e. mounts created on the host
generally appear in the unit processes' namespace, and mounts removed on the
host also disappear there too. In particular, note that mount propagation from
host to unit will result in unmodified mounts to be created in the unit's
namespace, i.e. writable mounts appearing on the host will be writable in the
unit's namespace too, even when propagated below a path marked with
ReadOnlyPaths=! Restricting access with these options hence does not
extend to submounts of a directory that are created later on. This means the
lock-down offered by that setting is not complete, and does not offer full
protection.
Note that the effect of these settings may be undone by privileged processes. In
order to set up an effective sandboxed environment for a unit it is thus
recommended to combine these settings with either
CapabilityBoundingSet=~CAP_SYS_ADMIN or
SystemCallFilter=~@mount.
Please be extra careful when applying these options to API file systems (a list
of them could be found in MountAPIVPS=), since they may be required for
basic system functionalities. Moreover, /run/ needs to be writable for setting
up mount namespace and propagation.
Simple allow-list example using these directives:
These options are only available for system services, or for services running in
per-user instances of the service manager when PrivateUsers= is
enabled.
TemporaryFileSystem=
[Service] ReadOnlyPaths=/ ReadWritePaths=/var /run InaccessiblePaths=-/lost+found NoExecPaths=/ ExecPaths=/usr/sbin/my_daemon /lib /lib64
Takes a space-separated list of mount points
for temporary file systems (tmpfs). If set, a new file system namespace is set
up for executed processes, and a temporary file system is mounted on each
mount point. This option may be specified more than once, in which case
temporary file systems are mounted on all listed mount points. If the empty
string is assigned to this option, the list is reset, and all prior
assignments have no effect. Each mount point may optionally be suffixed with a
colon (":") and mount options such as "size=10%" or
"ro". By default, each temporary file system is mounted with
"nodev,strictatime,mode=0755". These can be disabled by explicitly
specifying the corresponding mount options, e.g., "dev" or
"nostrictatime".
This is useful to hide files or directories not relevant to the processes
invoked by the unit, while necessary files or directories can be still
accessed by combining with BindPaths= or BindReadOnlyPaths=:
Example: if a unit has the following,
then the invoked processes by the unit cannot see any files or directories under
/var/ except for /var/lib/systemd or its contents.
This option is only available for system services, or for services running in
per-user instances of the service manager when PrivateUsers= is
enabled.
PrivateTmp=
TemporaryFileSystem=/var:ro BindReadOnlyPaths=/var/lib/systemd
Takes a boolean argument. If true, sets up a
new file system namespace for the executed processes and mounts private /tmp/
and /var/tmp/ directories inside it that are not shared by processes outside
of the namespace. This is useful to secure access to temporary files of the
process, but makes sharing between processes via /tmp/ or /var/tmp/
impossible. If true, all temporary files created by a service in these
directories will be removed after the service is stopped. Defaults to false.
It is possible to run two or more units within the same private /tmp/ and
/var/tmp/ namespace by using the JoinsNamespaceOf= directive, see
systemd.unit(5) for details. This setting is implied if
DynamicUser= is set. For this setting, the same restrictions regarding
mount propagation and privileges apply as for ReadOnlyPaths= and
related calls, see above. Enabling this setting has the side effect of adding
Requires= and After= dependencies on all mount units necessary
to access /tmp/ and /var/tmp/. Moreover an implicitly After= ordering
on systemd-tmpfiles-setup.service(8) is added.
Note that the implementation of this setting might be impossible (for example if
mount namespaces are not available), and the unit should be written in a way
that does not solely rely on this setting for security.
This option is only available for system services, or for services running in
per-user instances of the service manager when PrivateUsers= is
enabled.
PrivateDevices=
Takes a boolean argument. If true, sets up a
new /dev/ mount for the executed processes and only adds API pseudo devices
such as /dev/null, /dev/zero or /dev/random (as well as the pseudo TTY
subsystem) to it, but no physical devices such as /dev/sda, system memory
/dev/mem, system ports /dev/port and others. This is useful to turn off
physical device access by the executed process. Defaults to false.
Enabling this option will install a system call filter to block low-level I/O
system calls that are grouped in the @raw-io set, remove
CAP_MKNOD and CAP_SYS_RAWIO from the capability bounding set for
the unit, and set DevicePolicy=closed (see
systemd.resource-control(5) for details). Note that using this setting
will disconnect propagation of mounts from the service to the host
(propagation in the opposite direction continues to work). This means that
this setting may not be used for services which shall be able to install mount
points in the main mount namespace. The new /dev/ will be mounted read-only
and 'noexec'. The latter may break old programs which try to set up executable
memory by using mmap(2) of /dev/zero instead of using MAP_ANON.
For this setting the same restrictions regarding mount propagation and
privileges apply as for ReadOnlyPaths= and related calls, see above. If
turned on and if running in user mode, or in system mode, but without the
CAP_SYS_ADMIN capability (e.g. setting User=),
NoNewPrivileges=yes is implied.
Note that the implementation of this setting might be impossible (for example if
mount namespaces are not available), and the unit should be written in a way
that does not solely rely on this setting for security.
This option is only available for system services, or for services running in
per-user instances of the service manager when PrivateUsers= is
enabled.
When access to some but not all devices must be possible, the
DeviceAllow= setting might be used instead. See
systemd.resource-control(5).
PrivateNetwork=
Takes a boolean argument. If true, sets up a
new network namespace for the executed processes and configures only the
loopback network device "lo" inside it. No other network devices
will be available to the executed process. This is useful to turn off network
access by the executed process. Defaults to false. It is possible to run two
or more units within the same private network namespace by using the
JoinsNamespaceOf= directive, see systemd.unit(5) for details.
Note that this option will disconnect all socket families from the host,
including AF_NETLINK and AF_UNIX. Effectively, for
AF_NETLINK this means that device configuration events received from
systemd-udevd.service(8) are not delivered to the unit's processes. And
for AF_UNIX this has the effect that AF_UNIX sockets in the
abstract socket namespace of the host will become unavailable to the unit's
processes (however, those located in the file system will continue to be
accessible).
Note that the implementation of this setting might be impossible (for example if
network namespaces are not available), and the unit should be written in a way
that does not solely rely on this setting for security.
When this option is used on a socket unit any sockets bound on behalf of this
unit will be bound within a private network namespace. This may be combined
with JoinsNamespaceOf= to listen on sockets inside of network
namespaces of other services.
This option is only available for system services, or for services running in
per-user instances of the service manager when PrivateUsers= is
enabled.
NetworkNamespacePath=
Takes an absolute file system path refererring
to a Linux network namespace pseudo-file (i.e. a file like /proc/$PID/ns/net
or a bind mount or symlink to one). When set the invoked processes are added
to the network namespace referenced by that path. The path has to point to a
valid namespace file at the moment the processes are forked off. If this
option is used PrivateNetwork= has no effect. If this option is used
together with JoinsNamespaceOf= then it only has an effect if this unit
is started before any of the listed units that have PrivateNetwork= or
NetworkNamespacePath= configured, as otherwise the network namespace of
those units is reused.
When this option is used on a socket unit any sockets bound on behalf of this
unit will be bound within the specified network namespace.
This option is only available for system services, or for services running in
per-user instances of the service manager when PrivateUsers= is
enabled.
PrivateIPC=
Takes a boolean argument. If true, sets up a
new IPC namespace for the executed processes. Each IPC namespace has its own
set of System V IPC identifiers and its own POSIX message queue file system.
This is useful to avoid name clash of IPC identifiers. Defaults to false. It
is possible to run two or more units within the same private IPC namespace by
using the JoinsNamespaceOf= directive, see systemd.unit(5) for
details.
Note that IPC namespacing does not have an effect on AF_UNIX sockets,
which are the most common form of IPC used on Linux. Instead, AF_UNIX
sockets in the file system are subject to mount namespacing, and those in the
abstract namespace are subject to network namespacing. IPC namespacing only
has an effect on SysV IPC (which is mostly legacy) as well as POSIX message
queues (for which AF_UNIX/SOCK_SEQPACKET sockets are typically a
better replacement). IPC namespacing also has no effect on POSIX shared memory
(which is subject to mount namespacing) either. See ipc_namespaces(7)
for the details.
Note that the implementation of this setting might be impossible (for example if
IPC namespaces are not available), and the unit should be written in a way
that does not solely rely on this setting for security.
This option is only available for system services, or for services running in
per-user instances of the service manager when PrivateUsers= is
enabled.
IPCNamespacePath=
Takes an absolute file system path refererring
to a Linux IPC namespace pseudo-file (i.e. a file like /proc/$PID/ns/ipc or a
bind mount or symlink to one). When set the invoked processes are added to the
network namespace referenced by that path. The path has to point to a valid
namespace file at the moment the processes are forked off. If this option is
used PrivateIPC= has no effect. If this option is used together with
JoinsNamespaceOf= then it only has an effect if this unit is started
before any of the listed units that have PrivateIPC= or
IPCNamespacePath= configured, as otherwise the network namespace of
those units is reused.
This option is only available for system services, or for services running in
per-user instances of the service manager when PrivateUsers= is
enabled.
PrivateUsers=
Takes a boolean argument. If true, sets up a
new user namespace for the executed processes and configures a minimal user
and group mapping, that maps the "root" user and group as well as
the unit's own user and group to themselves and everything else to the
"nobody" user and group. This is useful to securely detach the user
and group databases used by the unit from the rest of the system, and thus to
create an effective sandbox environment. All files, directories, processes,
IPC objects and other resources owned by users/groups not equaling
"root" or the unit's own will stay visible from within the unit but
appear owned by the "nobody" user and group. If this mode is
enabled, all unit processes are run without privileges in the host user
namespace (regardless if the unit's own user/group is "root" or
not). Specifically this means that the process will have zero process
capabilities on the host's user namespace, but full capabilities within the
service's user namespace. Settings such as CapabilityBoundingSet= will
affect only the latter, and there's no way to acquire additional capabilities
in the host's user namespace. Defaults to off.
When this setting is set up by a per-user instance of the service manager, the
mapping of the "root" user and group to itself is omitted (unless
the user manager is root). Additionally, in the per-user instance manager
case, the user namespace will be set up before most other namespaces. This
means that combining PrivateUsers=true with other namespaces
will enable use of features not normally supported by the per-user instances
of the service manager.
This setting is particularly useful in conjunction with
RootDirectory=/RootImage=, as the need to synchronize the user
and group databases in the root directory and on the host is reduced, as the
only users and groups who need to be matched are "root",
"nobody" and the unit's own user and group.
Note that the implementation of this setting might be impossible (for example if
user namespaces are not available), and the unit should be written in a way
that does not solely rely on this setting for security.
ProtectHostname=
Takes a boolean argument. When set, sets up a
new UTS namespace for the executed processes. In addition, changing hostname
or domainname is prevented. Defaults to off.
Note that the implementation of this setting might be impossible (for example if
UTS namespaces are not available), and the unit should be written in a way
that does not solely rely on this setting for security.
Note that when this option is enabled for a service hostname changes no longer
propagate from the system into the service, it is hence not suitable for
services that need to take notice of system hostname changes dynamically.
If this setting is on, but the unit doesn't have the CAP_SYS_ADMIN
capability (e.g. services for which User= is set),
NoNewPrivileges=yes is implied.
This option is only available for system services, or for services running in
per-user instances of the service manager when PrivateUsers= is
enabled.
ProtectClock=
Takes a boolean argument. If set, writes to
the hardware clock or system clock will be denied. Defaults to off. Enabling
this option removes CAP_SYS_TIME and CAP_WAKE_ALARM from the
capability bounding set for this unit, installs a system call filter to block
calls that can set the clock, and DeviceAllow=char-rtc r is implied.
Note that the system calls are blocked altogether, the filter does not take
into account that some of the calls can be used to read the clock state with
some parameter combinations. Effectively, /dev/rtc0, /dev/rtc1, etc. are made
read-only to the service. See systemd.resource-control(5) for the
details about DeviceAllow=. If this setting is on, but the unit doesn't
have the CAP_SYS_ADMIN capability (e.g. services for which User=
is set), NoNewPrivileges=yes is implied.
It is recommended to turn this on for most services that do not need modify the
clock or check its state.
This option is only available for system services, or for services running in
per-user instances of the service manager when PrivateUsers= is
enabled.
ProtectKernelTunables=
Takes a boolean argument. If true, kernel
variables accessible through /proc/sys/, /sys/, /proc/sysrq-trigger,
/proc/latency_stats, /proc/acpi, /proc/timer_stats, /proc/fs and /proc/irq
will be made read-only to all processes of the unit. Usually, tunable kernel
variables should be initialized only at boot-time, for example with the
sysctl.d(5) mechanism. Few services need to write to these at runtime;
it is hence recommended to turn this on for most services. For this setting
the same restrictions regarding mount propagation and privileges apply as for
ReadOnlyPaths= and related calls, see above. Defaults to off. If this
setting is on, but the unit doesn't have the CAP_SYS_ADMIN capability
(e.g. services for which User= is set), NoNewPrivileges=yes is
implied. Note that this option does not prevent indirect changes to kernel
tunables effected by IPC calls to other processes. However,
InaccessiblePaths= may be used to make relevant IPC file system objects
inaccessible. If ProtectKernelTunables= is set, MountAPIVFS=yes
is implied.
This option is only available for system services, or for services running in
per-user instances of the service manager when PrivateUsers= is
enabled.
ProtectKernelModules=
Takes a boolean argument. If true, explicit
module loading will be denied. This allows module load and unload operations
to be turned off on modular kernels. It is recommended to turn this on for
most services that do not need special file systems or extra kernel modules to
work. Defaults to off. Enabling this option removes CAP_SYS_MODULE from
the capability bounding set for the unit, and installs a system call filter to
block module system calls, also /usr/lib/modules is made inaccessible. For
this setting the same restrictions regarding mount propagation and privileges
apply as for ReadOnlyPaths= and related calls, see above. Note that
limited automatic module loading due to user configuration or kernel mapping
tables might still happen as side effect of requested user operations, both
privileged and unprivileged. To disable module auto-load feature please see
sysctl.d(5) kernel.modules_disabled mechanism and
/proc/sys/kernel/modules_disabled documentation. If this setting is on, but
the unit doesn't have the CAP_SYS_ADMIN capability (e.g. services for
which User= is set), NoNewPrivileges=yes is implied.
This option is only available for system services, or for services running in
per-user instances of the service manager when PrivateUsers= is
enabled.
ProtectKernelLogs=
Takes a boolean argument. If true, access to
the kernel log ring buffer will be denied. It is recommended to turn this on
for most services that do not need to read from or write to the kernel log
ring buffer. Enabling this option removes CAP_SYSLOG from the
capability bounding set for this unit, and installs a system call filter to
block the syslog(2) system call (not to be confused with the libc API
syslog(3) for userspace logging). The kernel exposes its log buffer to
userspace via /dev/kmsg and /proc/kmsg. If enabled, these are made
inaccessible to all the processes in the unit. If this setting is on, but the
unit doesn't have the CAP_SYS_ADMIN capability (e.g. services for which
User= is set), NoNewPrivileges=yes is implied.
This option is only available for system services, or for services running in
per-user instances of the service manager when PrivateUsers= is
enabled.
ProtectControlGroups=
Takes a boolean argument. If true, the Linux
Control Groups ( cgroups(7)) hierarchies accessible through
/sys/fs/cgroup/ will be made read-only to all processes of the unit. Except
for container managers no services should require write access to the control
groups hierarchies; it is hence recommended to turn this on for most services.
For this setting the same restrictions regarding mount propagation and
privileges apply as for ReadOnlyPaths= and related calls, see above.
Defaults to off. If ProtectControlGroups= is set,
MountAPIVFS=yes is implied.
This option is only available for system services and is not supported for
services running in per-user instances of the service manager.
RestrictAddressFamilies=
Restricts the set of socket address families
accessible to the processes of this unit. Takes "none", or a
space-separated list of address family names to allow-list, such as
AF_UNIX, AF_INET or AF_INET6. When "none" is
specified, then all address families will be denied. When prefixed with
"~" the listed address families will be applied as deny list,
otherwise as allow list. Note that this restricts access to the
socket(2) system call only. Sockets passed into the process by other
means (for example, by using socket activation with socket units, see
systemd.socket(5)) are unaffected. Also, sockets created with
socketpair() (which creates connected AF_UNIX sockets only) are
unaffected. Note that this option has no effect on 32-bit x86, s390, s390x,
mips, mips-le, ppc, ppc-le, ppc64, ppc64-le and is ignored (but works
correctly on other ABIs, including x86-64). Note that on systems supporting
multiple ABIs (such as x86/x86-64) it is recommended to turn off alternative
ABIs for services, so that they cannot be used to circumvent the restrictions
of this option. Specifically, it is recommended to combine this option with
SystemCallArchitectures=native or similar. If running in user mode, or
in system mode, but without the CAP_SYS_ADMIN capability (e.g. setting
User=), NoNewPrivileges=yes is implied. By default, no
restrictions apply, all address families are accessible to processes. If
assigned the empty string, any previous address family restriction changes are
undone. This setting does not affect commands prefixed with "+".
Use this option to limit exposure of processes to remote access, in particular
via exotic and sensitive network protocols, such as AF_PACKET. Note
that in most cases, the local AF_UNIX address family should be included
in the configured allow list as it is frequently used for local communication,
including for syslog(2) logging.
RestrictFileSystems=
Restricts the set of filesystems processes of
this unit can open files on. Takes a space-separated list of filesystem names.
Any filesystem listed is made accessible to the unit's processes, access to
filesystem types not listed is prohibited (allow-listing). If the first
character of the list is "~", the effect is inverted: access to the
filesystems listed is prohibited (deny-listing). If the empty string is
assigned, access to filesystems is not restricted.
If you specify both types of this option (i.e. allow-listing and deny-listing),
the first encountered will take precedence and will dictate the default action
(allow access to the filesystem or deny it). Then the next occurrences of this
option will add or delete the listed filesystems from the set of the
restricted filesystems, depending on its type and the default action.
Example: if a unit has the following,
then access to ext4, tmpfs, and ext2 is allowed and access
to other filesystems is denied.
Example: if a unit has the following,
then only access tmpfs is allowed.
Example: if a unit has the following,
then only access to tmpfs is denied.
As the number of possible filesystems is large, predefined sets of filesystems
are provided. A set starts with "@" character, followed by name of
the set.
Table 3. Currently predefined filesystem sets
Use
systemd-analyze(1)'s filesystems command to retrieve a list of
filesystems defined on the local system.
Note that this setting might not be supported on some systems (for example if
the LSM eBPF hook is not enabled in the underlying kernel or if not using the
unified control group hierarchy). In that case this setting has no
effect.
RestrictNamespaces=
RestrictFileSystems=ext4 tmpfs RestrictFileSystems=ext2 ext4
RestrictFileSystems=ext4 tmpfs RestrictFileSystems=~ext4
RestrictFileSystems=~ext4 tmpfs RestrictFileSystems=ext4
Set | Description |
@basic-api | Basic filesystem API. |
@auxiliary-api | Auxiliary filesystem API. |
@common-block | Common block device filesystems. |
@historical-block | Historical block device filesystems. |
@network | Well-known network filesystems. |
@privileged-api | Privileged filesystem API. |
@temporary | Temporary filesystems: tmpfs, ramfs. |
@known | All known filesystems defined by the kernel. This list is defined statically in systemd based on a kernel version that was available when this systemd version was released. It will become progressively more out-of-date as the kernel is updated. |
Restricts access to Linux namespace
functionality for the processes of this unit. For details about Linux
namespaces, see namespaces(7). Either takes a boolean argument, or a
space-separated list of namespace type identifiers. If false (the default), no
restrictions on namespace creation and switching are made. If true, access to
any kind of namespacing is prohibited. Otherwise, a space-separated list of
namespace type identifiers must be specified, consisting of any combination
of: cgroup, ipc, net, mnt, pid, user
and uts. Any namespace type listed is made accessible to the unit's
processes, access to namespace types not listed is prohibited (allow-listing).
By prepending the list with a single tilde character ("~") the
effect may be inverted: only the listed namespace types will be made
inaccessible, all unlisted ones are permitted (deny-listing). If the empty
string is assigned, the default namespace restrictions are applied, which is
equivalent to false. This option may appear more than once, in which case the
namespace types are merged by OR, or by AND if the lines are
prefixed with "~" (see examples below). Internally, this setting
limits access to the unshare(2), clone(2) and setns(2)
system calls, taking the specified flags parameters into account. Note that
— if this option is used — in addition to restricting creation
and switching of the specified types of namespaces (or all of them, if true)
access to the setns() system call with a zero flags parameter is
prohibited. This setting is only supported on x86, x86-64, mips, mips-le,
mips64, mips64-le, mips64-n32, mips64-le-n32, ppc64, ppc64-le, s390 and s390x,
and enforces no restrictions on other architectures. If running in user mode,
or in system mode, but without the CAP_SYS_ADMIN capability (e.g.
setting User=), NoNewPrivileges=yes is implied.
Example: if a unit has the following,
then cgroup, ipc, and net are set. If the second line is
prefixed with "~", e.g.,
then, only ipc is set.
LockPersonality=
RestrictNamespaces=cgroup ipc RestrictNamespaces=cgroup net
RestrictNamespaces=cgroup ipc RestrictNamespaces=~cgroup net
Takes a boolean argument. If set, locks down
the personality(2) system call so that the kernel execution domain may
not be changed from the default or the personality selected with
Personality= directive. This may be useful to improve security, because
odd personality emulations may be poorly tested and source of vulnerabilities.
If running in user mode, or in system mode, but without the
CAP_SYS_ADMIN capability (e.g. setting User=),
NoNewPrivileges=yes is implied.
MemoryDenyWriteExecute=
Takes a boolean argument. If set, attempts to
create memory mappings that are writable and executable at the same time, or
to change existing memory mappings to become executable, or mapping shared
memory segments as executable, are prohibited. Specifically, a system call
filter is added that rejects mmap(2) system calls with both
PROT_EXEC and PROT_WRITE set, mprotect(2) or
pkey_mprotect(2) system calls with PROT_EXEC set and
shmat(2) system calls with SHM_EXEC set. Note that this option
is incompatible with programs and libraries that generate program code
dynamically at runtime, including JIT execution engines, executable stacks,
and code "trampoline" feature of various C compilers. This option
improves service security, as it makes harder for software exploits to change
running code dynamically. However, the protection can be circumvented, if the
service can write to a filesystem, which is not mounted with noexec
(such as /dev/shm), or it can use memfd_create(). This can be prevented
by making such file systems inaccessible to the service (e.g.
InaccessiblePaths=/dev/shm) and installing further system call filters
( SystemCallFilter=~memfd_create). Note that this feature is fully
available on x86-64, and partially on x86. Specifically, the shmat()
protection is not available on x86. Note that on systems supporting multiple
ABIs (such as x86/x86-64) it is recommended to turn off alternative ABIs for
services, so that they cannot be used to circumvent the restrictions of this
option. Specifically, it is recommended to combine this option with
SystemCallArchitectures=native or similar. If running in user mode, or
in system mode, but without the CAP_SYS_ADMIN capability (e.g. setting
User=), NoNewPrivileges=yes is implied.
RestrictRealtime=
Takes a boolean argument. If set, any attempts
to enable realtime scheduling in a process of the unit are refused. This
restricts access to realtime task scheduling policies such as
SCHED_FIFO, SCHED_RR or SCHED_DEADLINE. See
sched(7) for details about these scheduling policies. If running in
user mode, or in system mode, but without the CAP_SYS_ADMIN capability
(e.g. setting User=), NoNewPrivileges=yes is implied. Realtime
scheduling policies may be used to monopolize CPU time for longer periods of
time, and may hence be used to lock up or otherwise trigger Denial-of-Service
situations on the system. It is hence recommended to restrict access to
realtime scheduling to the few programs that actually require them. Defaults
to off.
RestrictSUIDSGID=
Takes a boolean argument. If set, any attempts
to set the set-user-ID (SUID) or set-group-ID (SGID) bits on files or
directories will be denied (for details on these bits see inode(7)). If
running in user mode, or in system mode, but without the CAP_SYS_ADMIN
capability (e.g. setting User=), NoNewPrivileges=yes is implied.
As the SUID/SGID bits are mechanisms to elevate privileges, and allow users to
acquire the identity of other users, it is recommended to restrict creation of
SUID/SGID files to the few programs that actually require them. Note that this
restricts marking of any type of file system object with these bits, including
both regular files and directories (where the SGID is a different meaning than
for files, see documentation). This option is implied if DynamicUser=
is enabled. Defaults to off.
RemoveIPC=
Takes a boolean parameter. If set, all System
V and POSIX IPC objects owned by the user and group the processes of this unit
are run as are removed when the unit is stopped. This setting only has an
effect if at least one of User=, Group= and DynamicUser=
are used. It has no effect on IPC objects owned by the root user.
Specifically, this removes System V semaphores, as well as System V and POSIX
shared memory segments and message queues. If multiple units use the same user
or group the IPC objects are removed when the last of these units is stopped.
This setting is implied if DynamicUser= is set.
This option is only available for system services and is not supported for
services running in per-user instances of the service manager.
PrivateMounts=
Takes a boolean parameter. If set, the
processes of this unit will be run in their own private file system (mount)
namespace with all mount propagation from the processes towards the host's
main file system namespace turned off. This means any file system mount points
established or removed by the unit's processes will be private to them and not
be visible to the host. However, file system mount points established or
removed on the host will be propagated to the unit's processes. See
mount_namespaces(7) for details on file system namespaces. Defaults to
off.
When turned on, this executes three operations for each invoked process: a new
CLONE_NEWNS namespace is created, after which all existing mounts are
remounted to MS_SLAVE to disable propagation from the unit's processes
to the host (but leaving propagation in the opposite direction in effect).
Finally, the mounts are remounted again to the propagation mode configured
with MountFlags=, see below.
File system namespaces are set up individually for each process forked off by
the service manager. Mounts established in the namespace of the process
created by ExecStartPre= will hence be cleaned up automatically as soon
as that process exits and will not be available to subsequent processes forked
off for ExecStart= (and similar applies to the various other commands
configured for units). Similarly, JoinsNamespaceOf= does not permit
sharing kernel mount namespaces between units, it only enables sharing of the
/tmp/ and /var/tmp/ directories.
Other file system namespace unit settings — PrivateMounts=,
PrivateTmp=, PrivateDevices=, ProtectSystem=,
ProtectHome=, ReadOnlyPaths=, InaccessiblePaths=,
ReadWritePaths=, ... — also enable file system namespacing in a
fashion equivalent to this option. Hence it is primarily useful to explicitly
request this behaviour if none of the other settings are used.
This option is only available for system services, or for services running in
per-user instances of the service manager when PrivateUsers= is
enabled.
MountFlags=
Takes a mount propagation setting:
shared, slave or private, which controls whether file
system mount points in the file system namespaces set up for this unit's
processes will receive or propagate mounts and unmounts from other file system
namespaces. See mount(2) for details on mount propagation, and the
three propagation flags in particular.
This setting only controls the final propagation setting in effect on all
mount points of the file system namespace created for each process of this
unit. Other file system namespacing unit settings (see the discussion in
PrivateMounts= above) will implicitly disable mount and unmount
propagation from the unit's processes towards the host by changing the
propagation setting of all mount points in the unit's file system namespace to
slave first. Setting this option to shared does not reestablish
propagation in that case.
If not set – but file system namespaces are enabled through another file
system namespace unit setting – shared mount propagation is
used, but — as mentioned — as slave is applied first,
propagation from the unit's processes to the host is still turned off.
It is not recommended to use private mount propagation for units, as this
means temporary mounts (such as removable media) of the host will stay mounted
and thus indefinitely busy in forked off processes, as unmount propagation
events won't be received by the file system namespace of the unit.
Usually, it is best to leave this setting unmodified, and use higher level file
system namespacing options instead, in particular PrivateMounts=, see
above.
This option is only available for system services, or for services running in
per-user instances of the service manager when PrivateUsers= is
enabled.
SYSTEM CALL FILTERING
SystemCallFilter=Takes a space-separated list of system call
names. If this setting is used, all system calls executed by the unit
processes except for the listed ones will result in immediate process
termination with the SIGSYS signal (allow-listing). (See
SystemCallErrorNumber= below for changing the default action). If the
first character of the list is "~", the effect is inverted: only the
listed system calls will result in immediate process termination
(deny-listing). Deny-listed system calls and system call groups may optionally
be suffixed with a colon (":") and "errno" error number
(between 0 and 4095) or errno name such as EPERM, EACCES or
EUCLEAN (see errno(3) for a full list). This value will be
returned when a deny-listed system call is triggered, instead of terminating
the processes immediately. Special setting "kill" can be used to
explicitly specify killing. This value takes precedence over the one given in
SystemCallErrorNumber=, see below. If running in user mode, or in
system mode, but without the CAP_SYS_ADMIN capability (e.g. setting
User=), NoNewPrivileges=yes is implied. This feature makes use
of the Secure Computing Mode 2 interfaces of the kernel ('seccomp filtering')
and is useful for enforcing a minimal sandboxing environment. Note that the
execve(), exit(), exit_group(), getrlimit(),
rt_sigreturn(), sigreturn() system calls and the system calls
for querying time and sleeping are implicitly allow-listed and do not need to
be listed explicitly. This option may be specified more than once, in which
case the filter masks are merged. If the empty string is assigned, the filter
is reset, all prior assignments will have no effect. This does not affect
commands prefixed with "+".
Note that on systems supporting multiple ABIs (such as x86/x86-64) it is
recommended to turn off alternative ABIs for services, so that they cannot be
used to circumvent the restrictions of this option. Specifically, it is
recommended to combine this option with SystemCallArchitectures=native
or similar.
Note that strict system call filters may impact execution and error handling
code paths of the service invocation. Specifically, access to the
execve() system call is required for the execution of the service
binary — if it is blocked service invocation will necessarily fail.
Also, if execution of the service binary fails for some reason (for example:
missing service executable), the error handling logic might require access to
an additional set of system calls in order to process and log this failure
correctly. It might be necessary to temporarily disable system call filters in
order to simplify debugging of such failures.
If you specify both types of this option (i.e. allow-listing and deny-listing),
the first encountered will take precedence and will dictate the default action
(termination or approval of a system call). Then the next occurrences of this
option will add or delete the listed system calls from the set of the filtered
system calls, depending of its type and the default action. (For example, if
you have started with an allow list rule for read() and write(),
and right after it add a deny list rule for write(), then
write() will be removed from the set.)
As the number of possible system calls is large, predefined sets of system calls
are provided. A set starts with "@" character, followed by name of
the set.
Table 4. Currently predefined system call sets
Note, that as new system calls are added to the kernel, additional system calls
might be added to the groups above. Contents of the sets may also change
between systemd versions. In addition, the list of system calls depends on the
kernel version and architecture for which systemd was compiled. Use
systemd-analyze syscall-filter to list the actual list of system
calls in each filter.
Generally, allow-listing system calls (rather than deny-listing) is the safer
mode of operation. It is recommended to enforce system call allow lists for
all long-running system services. Specifically, the following lines are a
relatively safe basic choice for the majority of system services:
Note that various kernel system calls are defined redundantly: there are
multiple system calls for executing the same operation. For example, the
pidfd_send_signal() system call may be used to execute operations
similar to what can be done with the older kill() system call, hence
blocking the latter without the former only provides weak protection. Since
new system calls are added regularly to the kernel as development progresses,
keeping system call deny lists comprehensive requires constant work. It is
thus recommended to use allow-listing instead, which offers the benefit that
new system calls are by default implicitly blocked until the allow list is
updated.
Also note that a number of system calls are required to be accessible for the
dynamic linker to work. The dynamic linker is required for running most
regular programs (specifically: all dynamic ELF binaries, which is how most
distributions build packaged programs). This means that blocking these system
calls (which include open(), openat() or mmap()) will
make most programs typically shipped with generic distributions unusable.
It is recommended to combine the file system namespacing related options with
SystemCallFilter=~@mount, in order to prohibit the unit's processes to
undo the mappings. Specifically these are the options PrivateTmp=,
PrivateDevices=, ProtectSystem=, ProtectHome=,
ProtectKernelTunables=, ProtectControlGroups=,
ProtectKernelLogs=, ProtectClock=, ReadOnlyPaths=,
InaccessiblePaths= and ReadWritePaths=.
SystemCallErrorNumber=
Set | Description |
@aio | Asynchronous I/O (io_setup(2), io_submit(2), and related calls) |
@basic-io | System calls for basic I/O: reading, writing, seeking, file descriptor duplication and closing ( read(2), write(2), and related calls) |
@chown | Changing file ownership (chown(2), fchownat(2), and related calls) |
@clock | System calls for changing the system clock (adjtimex(2), settimeofday(2), and related calls) |
@cpu-emulation | System calls for CPU emulation functionality (vm86(2) and related calls) |
@debug | Debugging, performance monitoring and tracing functionality (ptrace(2), perf_event_open(2) and related calls) |
@file-system | File system operations: opening, creating files and directories for read and write, renaming and removing them, reading file properties, or creating hard and symbolic links |
@io-event | Event loop system calls (poll(2), select(2), epoll(7), eventfd(2) and related calls) |
@ipc | Pipes, SysV IPC, POSIX Message Queues and other IPC (mq_overview(7), svipc(7)) |
@keyring | Kernel keyring access (keyctl(2) and related calls) |
@memlock | Locking of memory in RAM (mlock(2), mlockall(2) and related calls) |
@module | Loading and unloading of kernel modules (init_module(2), delete_module(2) and related calls) |
@mount | Mounting and unmounting of file systems (mount(2), chroot(2), and related calls) |
@network-io | Socket I/O (including local AF_UNIX): socket(7), unix(7) |
@obsolete | Unusual, obsolete or unimplemented (create_module(2), gtty(2), ...) |
@privileged | All system calls which need super-user capabilities (capabilities(7)) |
@process | Process control, execution, namespacing operations (clone(2), kill(2), namespaces(7), ...) |
@raw-io | Raw I/O port access (ioperm(2), iopl(2), pciconfig_read(), ...) |
@reboot | System calls for rebooting and reboot preparation (reboot(2), kexec(), ...) |
@resources | System calls for changing resource limits, memory and scheduling parameters ( setrlimit(2), setpriority(2), ...) |
@setuid | System calls for changing user ID and group ID credentials, (setuid(2), setgid(2), setresuid(2), ...) |
@signal | System calls for manipulating and handling process signals (signal(2), sigprocmask(2), ...) |
@swap | System calls for enabling/disabling swap devices (swapon(2), swapoff(2)) |
@sync | Synchronizing files and memory to disk (fsync(2), msync(2), and related calls) |
@system-service | A reasonable set of system calls used by common system services, excluding any special purpose calls. This is the recommended starting point for allow-listing system calls for system services, as it contains what is typically needed by system services, but excludes overly specific interfaces. For example, the following APIs are excluded: "@clock", "@mount", "@swap", "@reboot". |
@timer | System calls for scheduling operations by time (alarm(2), timer_create(2), ...) |
@known | All system calls defined by the kernel. This list is defined statically in systemd based on a kernel version that was available when this systemd version was released. It will become progressively more out-of-date as the kernel is updated. |
[Service] SystemCallFilter=@system-service SystemCallErrorNumber=EPERM
Takes an "errno" error number
(between 1 and 4095) or errno name such as EPERM, EACCES or
EUCLEAN, to return when the system call filter configured with
SystemCallFilter= is triggered, instead of terminating the process
immediately. See errno(3) for a full list of error codes. When this
setting is not used, or when the empty string or the special setting
"kill" is assigned, the process will be terminated immediately when
the filter is triggered.
SystemCallArchitectures=
Takes a space-separated list of architecture
identifiers to include in the system call filter. The known architecture
identifiers are the same as for ConditionArchitecture= described in
systemd.unit(5), as well as x32, mips64-n32,
mips64-le-n32, and the special identifier native. The special
identifier native implicitly maps to the native architecture of the
system (or more precisely: to the architecture the system manager is compiled
for). If running in user mode, or in system mode, but without the
CAP_SYS_ADMIN capability (e.g. setting User=),
NoNewPrivileges=yes is implied. By default, this option is set to the
empty list, i.e. no filtering is applied.
If this setting is used, processes of this unit will only be permitted to call
native system calls, and system calls of the specified architectures. For the
purposes of this option, the x32 architecture is treated as including x86-64
system calls. However, this setting still fulfills its purpose, as explained
below, on x32.
System call filtering is not equally effective on all architectures. For
example, on x86 filtering of network socket-related calls is not possible, due
to ABI limitations — a limitation that x86-64 does not have, however.
On systems supporting multiple ABIs at the same time — such as
x86/x86-64 — it is hence recommended to limit the set of permitted
system call architectures so that secondary ABIs may not be used to circumvent
the restrictions applied to the native ABI of the system. In particular,
setting SystemCallArchitectures=native is a good choice for disabling
non-native ABIs.
System call architectures may also be restricted system-wide via the
SystemCallArchitectures= option in the global configuration. See
systemd-system.conf(5) for details.
SystemCallLog=
Takes a space-separated list of system call
names. If this setting is used, all system calls executed by the unit
processes for the listed ones will be logged. If the first character of the
list is "~", the effect is inverted: all system calls except the
listed system calls will be logged. If running in user mode, or in system
mode, but without the CAP_SYS_ADMIN capability (e.g. setting
User=), NoNewPrivileges=yes is implied. This feature makes use
of the Secure Computing Mode 2 interfaces of the kernel ('seccomp filtering')
and is useful for auditing or setting up a minimal sandboxing environment.
This option may be specified more than once, in which case the filter masks
are merged. If the empty string is assigned, the filter is reset, all prior
assignments will have no effect. This does not affect commands prefixed with
"+".
ENVIRONMENT
Environment=Sets environment variables for executed
processes. Each line is unquoted using the rules described in
"Quoting" section in systemd.syntax(7) and becomes a list of
variable assignments. If you need to assign a value containing spaces or the
equals sign to a variable, put quotes around the whole assignment. Variable
expansion is not performed inside the strings and the "$" character
has no special meaning. Specifier expansion is performed, see the
"Specifiers" section in systemd.unit(5).
This option may be specified more than once, in which case all listed variables
will be set. If the same variable is listed twice, the later setting will
override the earlier setting. If the empty string is assigned to this option,
the list of environment variables is reset, all prior assignments have no
effect.
The names of the variables can contain ASCII letters, digits, and the underscore
character. Variable names cannot be empty or start with a digit. In variable
values, most characters are allowed, but non-printable characters are
currently rejected.
Example:
gives three variables "VAR1", "VAR2", "VAR3" with
the values "word1 word2", "word3", "$word 5 6".
See environ(7) for details about environment variables.
Note that environment variables are not suitable for passing secrets (such as
passwords, key material, ...) to service processes. Environment variables set
for a unit are exposed to unprivileged clients via D-Bus IPC, and generally
not understood as being data that requires protection. Moreover, environment
variables are propagated down the process tree, including across security
boundaries (such as setuid/setgid executables), and hence might leak to
processes that should not have access to the secret data. Use
LoadCredential=, LoadCredentialEncrypted= or
SetCredentialEncrypted= (see below) to pass data to unit processes
securely.
EnvironmentFile=
Environment="VAR1=word1 word2" VAR2=word3 "VAR3=$word 5 6"
Similar to Environment=, but reads the
environment variables from a text file. The text file should contain
newline-separated variable assignments. Empty lines, lines without an
"=" separator, or lines starting with ";" or "#"
will be ignored, which may be used for commenting. The file must be UTF-8
encoded. Valid characters are unicode scalar values[7] other than
noncharacters[8], U+0000 NUL, and U+FEFF byte order mark[9].
Control codes other than NUL are allowed.
In the file, an unquoted value after the "=" is parsed with the same
backslash-escape rules as unquoted text[10] in a POSIX shell, but
unlike in a shell, interior whitespace is preserved and quotes after the first
non-whitespace character are preserved. Leading and trailing whitespace
(space, tab, carriage return) is discarded, but interior whitespace within the
line is preserved verbatim. A line ending with a backslash will be continued
to the following one, with the newline itself discarded. A backslash
"\" followed by any character other than newline will preserve the
following character, so that "\\" will become the value
"\".
In the file, a "'"-quoted value after the "=" can span
multiple lines and contain any character verbatim other than single quote,
like single-quoted text[11] in a POSIX shell. No backslash-escape
sequences are recognized. Leading and trailing whitespace outside of the
single quotes is discarded.
In the file, a """-quoted value after the "=" can span
multiple lines, and the same escape sequences are recognized as in
double-quoted text[12] of a POSIX shell. Backslash ("\")
followed by any of ""\`$" will preserve that character. A
backslash followed by newline is a line continuation, and the newline itself
is discarded. A backslash followed by any other character is ignored; both the
backslash and the following character are preserved verbatim. Leading and
trailing whitespace outside of the double quotes is discarded.
The argument passed should be an absolute filename or wildcard expression,
optionally prefixed with "-", which indicates that if the file does
not exist, it will not be read and no error or warning message is logged. This
option may be specified more than once in which case all specified files are
read. If the empty string is assigned to this option, the list of file to read
is reset, all prior assignments have no effect.
The files listed with this directive will be read shortly before the process is
executed (more specifically, after all processes from a previous unit state
terminated. This means you can generate these files in one unit state, and
read it with this option in the next. The files are read from the file system
of the service manager, before any file system changes like bind mounts take
place).
Settings from these files override settings made with Environment=. If
the same variable is set twice from these files, the files will be read in the
order they are specified and the later setting will override the earlier
setting.
PassEnvironment=
Pass environment variables set for the system
service manager to executed processes. Takes a space-separated list of
variable names. This option may be specified more than once, in which case all
listed variables will be passed. If the empty string is assigned to this
option, the list of environment variables to pass is reset, all prior
assignments have no effect. Variables specified that are not set for the
system manager will not be passed and will be silently ignored. Note that this
option is only relevant for the system service manager, as system services by
default do not automatically inherit any environment variables set for the
service manager itself. However, in case of the user service manager all
environment variables are passed to the executed processes anyway, hence this
option is without effect for the user service manager.
Variables set for invoked processes due to this setting are subject to being
overridden by those configured with Environment= or
EnvironmentFile=.
Example:
passes three variables "VAR1", "VAR2", "VAR3" with
the values set for those variables in PID1.
See environ(7) for details about environment variables.
UnsetEnvironment=
PassEnvironment=VAR1 VAR2 VAR3
Explicitly unset environment variable
assignments that would normally be passed from the service manager to invoked
processes of this unit. Takes a space-separated list of variable names or
variable assignments. This option may be specified more than once, in which
case all listed variables/assignments will be unset. If the empty string is
assigned to this option, the list of environment variables/assignments to
unset is reset. If a variable assignment is specified (that is: a variable
name, followed by "=", followed by its value), then any environment
variable matching this precise assignment is removed. If a variable name is
specified (that is a variable name without any following "=" or
value), then any assignment matching the variable name, regardless of its
value is removed. Note that the effect of UnsetEnvironment= is applied
as final step when the environment list passed to executed processes is
compiled. That means it may undo assignments from any configuration source,
including assignments made through Environment= or
EnvironmentFile=, inherited from the system manager's global set of
environment variables, inherited via PassEnvironment=, set by the
service manager itself (such as $NOTIFY_SOCKET and such), or set by a
PAM module (in case PAMName= is used).
See "Environment Variables in Spawned Processes" below for a
description of how those settings combine to form the inherited environment.
See environ(7) for general information about environment
variables.
LOGGING AND STANDARD INPUT/OUTPUT
StandardInput=Controls where file descriptor 0 (STDIN) of
the executed processes is connected to. Takes one of null, tty,
tty-force, tty-fail, data,
file:path, socket or fd:name.
If null is selected, standard input will be connected to /dev/null, i.e.
all read attempts by the process will result in immediate EOF.
If tty is selected, standard input is connected to a TTY (as configured
by TTYPath=, see below) and the executed process becomes the
controlling process of the terminal. If the terminal is already being
controlled by another process, the executed process waits until the current
controlling process releases the terminal.
tty-force is similar to tty, but the executed process is
forcefully and immediately made the controlling process of the terminal,
potentially removing previous controlling processes from the terminal.
tty-fail is similar to tty, but if the terminal already has a
controlling process start-up of the executed process fails.
The data option may be used to configure arbitrary textual or binary data
to pass via standard input to the executed process. The data to pass is
configured via StandardInputText=/StandardInputData= (see
below). Note that the actual file descriptor type passed (memory file, regular
file, UNIX pipe, ...) might depend on the kernel and available privileges. In
any case, the file descriptor is read-only, and when read returns the
specified data followed by EOF.
The file:path option may be used to connect a specific file
system object to standard input. An absolute path following the ":"
character is expected, which may refer to a regular file, a FIFO or special
file. If an AF_UNIX socket in the file system is specified, a stream
socket is connected to it. The latter is useful for connecting standard input
of processes to arbitrary system services.
The socket option is valid in socket-activated services only, and
requires the relevant socket unit file (see systemd.socket(5) for
details) to have Accept=yes set, or to specify a single socket only. If
this option is set, standard input will be connected to the socket the service
was activated from, which is primarily useful for compatibility with daemons
designed for use with the traditional inetd(8) socket activation daemon
( $LISTEN_FDS (and related) environment variables are not passed when
socket value is configured).
The fd:name option connects standard input to a specific,
named file descriptor provided by a socket unit. The name may be specified as
part of this option, following a ":" character (e.g.
"fd:foobar"). If no name is specified, the name "stdin" is
implied (i.e. "fd" is equivalent to "fd:stdin"). At least
one socket unit defining the specified name must be provided via the
Sockets= option, and the file descriptor name may differ from the name
of its containing socket unit. If multiple matches are found, the first one
will be used. See FileDescriptorName= in systemd.socket(5) for
more details about named file descriptors and their ordering.
This setting defaults to null, unless
StandardInputText=/StandardInputData= are set, in which case it
defaults to data.
StandardOutput=
Controls where file descriptor 1 (stdout) of
the executed processes is connected to. Takes one of inherit,
null, tty, journal, kmsg, journal+console,
kmsg+console, file:path,
append:path, truncate:path,
socket or fd:name.
inherit duplicates the file descriptor of standard input for standard
output.
null connects standard output to /dev/null, i.e. everything written to it
will be lost.
tty connects standard output to a tty (as configured via TTYPath=,
see below). If the TTY is used for output only, the executed process will not
become the controlling process of the terminal, and will not fail or wait for
other processes to release the terminal.
journal connects standard output with the journal, which is accessible
via journalctl(1). Note that everything that is written to kmsg (see
below) is implicitly stored in the journal as well, the specific option listed
below is hence a superset of this one. (Also note that any external,
additional syslog daemons receive their log data from the journal, too, hence
this is the option to use when logging shall be processed with such a daemon.)
kmsg connects standard output with the kernel log buffer which is
accessible via dmesg(1), in addition to the journal. The journal daemon
might be configured to send all logs to kmsg anyway, in which case this option
is no different from journal.
journal+console and kmsg+console work in a similar way as the two
options above but copy the output to the system console as well.
The file:path option may be used to connect a specific file
system object to standard output. The semantics are similar to the same option
of StandardInput=, see above. If path refers to a regular file
on the filesystem, it is opened (created if it doesn't exist yet) for writing
at the beginning of the file, but without truncating it. If standard input and
output are directed to the same file path, it is opened only once — for
reading as well as writing — and duplicated. This is particularly
useful when the specified path refers to an AF_UNIX socket in the file
system, as in that case only a single stream connection is created for both
input and output.
append:path is similar to file:path
above, but it opens the file in append mode.
truncate:path is similar to file:path
above, but it truncates the file when opening it. For units with multiple
command lines, e.g. Type=oneshot services with multiple
ExecStart=, or services with ExecCondition=,
ExecStartPre= or ExecStartPost=, the output file is reopened and
therefore re-truncated for each command line. If the output file is truncated
while another process still has the file open, e.g. by an ExecReload=
running concurrently with an ExecStart=, and the other process
continues writing to the file without adjusting its offset, then the space
between the file pointers of the two processes may be filled with NUL
bytes, producing a sparse file. Thus, truncate:path is
typically only useful for units where only one process runs at a time, such as
services with a single ExecStart= and no ExecStartPost=,
ExecReload=, ExecStop= or similar.
socket connects standard output to a socket acquired via socket
activation. The semantics are similar to the same option of
StandardInput=, see above.
The fd:name option connects standard output to a specific,
named file descriptor provided by a socket unit. A name may be specified as
part of this option, following a ":" character (e.g. "fd:
foobar"). If no name is specified, the name "stdout" is
implied (i.e. "fd" is equivalent to "fd:stdout"). At least
one socket unit defining the specified name must be provided via the
Sockets= option, and the file descriptor name may differ from the name
of its containing socket unit. If multiple matches are found, the first one
will be used. See FileDescriptorName= in systemd.socket(5) for
more details about named descriptors and their ordering.
If the standard output (or error output, see below) of a unit is connected to
the journal or the kernel log buffer, the unit will implicitly gain a
dependency of type After= on systemd-journald.socket (also see the
"Implicit Dependencies" section above). Also note that in this case
stdout (or stderr, see below) will be an AF_UNIX stream socket, and not
a pipe or FIFO that can be re-opened. This means when executing shell scripts
the construct echo "hello" > /dev/stderr for writing text
to stderr will not work. To mitigate this use the construct echo
"hello" >&2 instead, which is mostly equivalent and
avoids this pitfall.
If StandardInput= is set to one of tty, tty-force,
tty-fail, socket, or fd:name, this setting
defaults to inherit.
In other cases, this setting defaults to the value set with
DefaultStandardOutput= in systemd-system.conf(5), which defaults
to journal. Note that setting this parameter might result in additional
dependencies to be added to the unit (see above).
StandardError=
Controls where file descriptor 2 (stderr) of
the executed processes is connected to. The available options are identical to
those of StandardOutput=, with some exceptions: if set to
inherit the file descriptor used for standard output is duplicated for
standard error, while fd:name will use a default file
descriptor name of "stderr".
This setting defaults to the value set with DefaultStandardError= in
systemd-system.conf(5), which defaults to inherit. Note that
setting this parameter might result in additional dependencies to be added to
the unit (see above).
StandardInputText=, StandardInputData=
Configures arbitrary textual or binary data to
pass via file descriptor 0 (STDIN) to the executed processes. These settings
have no effect unless StandardInput= is set to data (which is
the default if StandardInput= is not set otherwise, but
StandardInputText=/ StandardInputData= is). Use this option to
embed process input data directly in the unit file.
StandardInputText= accepts arbitrary textual data. C-style escapes for
special characters as well as the usual "%"-specifiers are resolved.
Each time this setting is used the specified text is appended to the per-unit
data buffer, followed by a newline character (thus every use appends a new
line to the end of the buffer). Note that leading and trailing whitespace of
lines configured with this option is removed. If an empty line is specified
the buffer is cleared (hence, in order to insert an empty line, add an
additional "\n" to the end or beginning of a line).
StandardInputData= accepts arbitrary binary data, encoded in
Base64[13]. No escape sequences or specifiers are resolved. Any
whitespace in the encoded version is ignored during decoding.
Note that StandardInputText= and StandardInputData= operate on the
same data buffer, and may be mixed in order to configure both binary and
textual data for the same input stream. The textual or binary data is joined
strictly in the order the settings appear in the unit file. Assigning an empty
string to either will reset the data buffer.
Please keep in mind that in order to maintain readability long unit file
settings may be split into multiple lines, by suffixing each line (except for
the last) with a "\" character (see systemd.unit(5) for
details). This is particularly useful for large data configured with these two
options. Example:
LogLevelMax=
... StandardInput=data StandardInputData=V2XigLJyZSBubyBzdHJhbmdlcnMgdG8gbG92ZQpZb3Uga25vdyB0aGUgcnVsZXMgYW5kIHNvIGRv \ IEkKQSBmdWxsIGNvbW1pdG1lbnQncyB3aGF0IEnigLJtIHRoaW5raW5nIG9mCllvdSB3b3VsZG4n \ dCBnZXQgdGhpcyBmcm9tIGFueSBvdGhlciBndXkKSSBqdXN0IHdhbm5hIHRlbGwgeW91IGhvdyBJ \ J20gZmVlbGluZwpHb3R0YSBtYWtlIHlvdSB1bmRlcnN0YW5kCgpOZXZlciBnb25uYSBnaXZlIHlv \ dSB1cApOZXZlciBnb25uYSBsZXQgeW91IGRvd24KTmV2ZXIgZ29ubmEgcnVuIGFyb3VuZCBhbmQg \ ZGVzZXJ0IHlvdQpOZXZlciBnb25uYSBtYWtlIHlvdSBjcnkKTmV2ZXIgZ29ubmEgc2F5IGdvb2Ri \ eWUKTmV2ZXIgZ29ubmEgdGVsbCBhIGxpZSBhbmQgaHVydCB5b3UK ...
Configures filtering by log level of log
messages generated by this unit. Takes a syslog log level, one of
emerg (lowest log level, only highest priority messages), alert,
crit, err, warning, notice, info,
debug (highest log level, also lowest priority messages). See
syslog(3) for details. By default no filtering is applied (i.e. the
default maximum log level is debug). Use this option to configure the
logging system to drop log messages of a specific service above the specified
level. For example, set LogLevelMax=info in order to turn off
debug logging of a particularly chatty unit. Note that the configured level is
applied to any log messages written by any of the processes belonging to this
unit, as well as any log messages written by the system manager process (PID
1) in reference to this unit, sent via any supported logging protocol. The
filtering is applied early in the logging pipeline, before any kind of further
processing is done. Moreover, messages which pass through this filter
successfully might still be dropped by filters applied at a later stage in the
logging subsystem. For example, MaxLevelStore= configured in
journald.conf(5) might prohibit messages of higher log levels to be
stored on disk, even though the per-unit LogLevelMax= permitted it to
be processed.
LogExtraFields=
Configures additional log metadata fields to
include in all log records generated by processes associated with this unit.
This setting takes one or more journal field assignments in the format
"FIELD=VALUE" separated by whitespace. See
systemd.journal-fields(7) for details on the journal field concept.
Even though the underlying journal implementation permits binary field values,
this setting accepts only valid UTF-8 values. To include space characters in a
journal field value, enclose the assignment in double quotes ("). The
usual specifiers are expanded in all assignments (see below). Note that this
setting is not only useful for attaching additional metadata to log records of
a unit, but given that all fields and values are indexed may also be used to
implement cross-unit log record matching. Assign an empty string to reset the
list.
LogRateLimitIntervalSec=, LogRateLimitBurst=
Configures the rate limiting that is applied
to messages generated by this unit. If, in the time interval defined by
LogRateLimitIntervalSec=, more messages than specified in
LogRateLimitBurst= are logged by a service, all further messages within
the interval are dropped until the interval is over. A message about the
number of dropped messages is generated. The time specification for
LogRateLimitIntervalSec= may be specified in the following units:
"s", "min", "h", "ms", "us"
(see systemd.time(7) for details). The default settings are set by
RateLimitIntervalSec= and RateLimitBurst= configured in
journald.conf(5).
LogNamespace=
Run the unit's processes in the specified
journal namespace. Expects a short user-defined string identifying the
namespace. If not used the processes of the service are run in the default
journal namespace, i.e. their log stream is collected and processed by
systemd-journald.service. If this option is used any log data generated by
processes of this unit (regardless if via the syslog(), journal native
logging or stdout/stderr logging) is collected and processed by an instance of
the [email protected] template unit, which manages the specified
namespace. The log data is stored in a data store independent from the default
log namespace's data store. See systemd-journald.service(8) for details
about journal namespaces.
Internally, journal namespaces are implemented through Linux mount namespacing
and over-mounting the directory that contains the relevant AF_UNIX
sockets used for logging in the unit's mount namespace. Since mount namespaces
are used this setting disconnects propagation of mounts from the unit's
processes to the host, similarly to how ReadOnlyPaths= and similar
settings describe above work. Journal namespaces may hence not be used for
services that need to establish mount points on the host.
When this option is used the unit will automatically gain ordering and
requirement dependencies on the two socket units associated with the
[email protected] instance so that they are automatically established
prior to the unit starting up. Note that when this option is used log output
of this service does not appear in the regular journalctl(1) output,
unless the --namespace= option is used.
This option is only available for system services and is not supported for
services running in per-user instances of the service manager.
SyslogIdentifier=
Sets the process name ("syslog
tag") to prefix log lines sent to the logging system or the kernel log
buffer with. If not set, defaults to the process name of the executed process.
This option is only useful when StandardOutput= or
StandardError= are set to journal or kmsg (or to the same
settings in combination with +console) and only applies to log messages
written to stdout or stderr.
SyslogFacility=
Sets the syslog facility identifier to
use when logging. One of kern, user, mail, daemon,
auth, syslog, lpr, news, uucp, cron,
authpriv, ftp, local0, local1, local2,
local3, local4, local5, local6 or local7.
See syslog(3) for details. This option is only useful when
StandardOutput= or StandardError= are set to journal or
kmsg (or to the same settings in combination with +console), and
only applies to log messages written to stdout or stderr. Defaults to
daemon.
SyslogLevel=
The default syslog log level to use
when logging to the logging system or the kernel log buffer. One of
emerg, alert, crit, err, warning,
notice, info, debug. See syslog(3) for details.
This option is only useful when StandardOutput= or
StandardError= are set to journal or kmsg (or to the same
settings in combination with +console), and only applies to log
messages written to stdout or stderr. Note that individual lines output by
executed processes may be prefixed with a different log level which can be
used to override the default log level specified here. The interpretation of
these prefixes may be disabled with SyslogLevelPrefix=, see below. For
details, see sd-daemon(3). Defaults to info.
SyslogLevelPrefix=
Takes a boolean argument. If true and
StandardOutput= or StandardError= are set to journal or
kmsg (or to the same settings in combination with +console), log
lines written by the executed process that are prefixed with a log level will
be processed with this log level set but the prefix removed. If set to false,
the interpretation of these prefixes is disabled and the logged lines are
passed on as-is. This only applies to log messages written to stdout or
stderr. For details about this prefixing see sd-daemon(3). Defaults to
true.
TTYPath=
Sets the terminal device node to use if
standard input, output, or error are connected to a TTY (see above). Defaults
to /dev/console.
TTYReset=
Reset the terminal device specified with
TTYPath= before and after execution. Defaults to "no".
TTYVHangup=
Disconnect all clients which have opened the
terminal device specified with TTYPath= before and after execution.
Defaults to "no".
TTYRows=, TTYColumns=
Configure the size of the TTY specified with
TTYPath=. If unset or set to the empty string, the kernel default is
used.
TTYVTDisallocate=
If the terminal device specified with
TTYPath= is a virtual console terminal, try to deallocate the TTY
before and after execution. This ensures that the screen and scrollback buffer
is cleared. Defaults to "no".
CREDENTIALS
LoadCredential=ID[:PATH], LoadCredentialEncrypted=ID[:PATH]Pass a credential to the unit. Credentials are
limited-size binary or textual objects that may be passed to unit processes.
They are primarily used for passing cryptographic keys (both public and
private) or certificates, user account information or identity information
from host to services. The data is accessible from the unit's processes via
the file system, at a read-only location that (if possible and permitted) is
backed by non-swappable memory. The data is only accessible to the user
associated with the unit, via the User=/DynamicUser= settings
(as well as the superuser). When available, the location of credentials is
exported as the $CREDENTIALS_DIRECTORY environment variable to the
unit's processes.
The LoadCredential= setting takes a textual ID to use as name for a
credential plus a file system path, separated by a colon. The ID must be a
short ASCII string suitable as filename in the filesystem, and may be chosen
freely by the user. If the specified path is absolute it is opened as regular
file and the credential data is read from it. If the absolute path refers to
an AF_UNIX stream socket in the file system a connection is made to it
(only once at unit start-up) and the credential data read from the connection,
providing an easy IPC integration point for dynamically transferring
credentials from other services.
If the specified path is not absolute and itself qualifies as valid credential
identifier it is attempted to find a credential that the service manager
itself received under the specified name — which may be used to
propagate credentials from an invoking environment (e.g. a container manager
that invoked the service manager) into a service. If no matching system
credential is found, the directories /etc/credstore/, /run/credstore/ and
/usr/lib/credstore/ are searched for files under the credential's name
— which hence are recommended locations for credential data on disk. If
LoadCredentialEncrypted= is used /run/credstore.encrypted/,
/etc/credstore.encrypted/, and /usr/lib/credstore.encrypted/ are searched as
well.
If the file system path is omitted it is chosen identical to the credential
name, i.e. this is a terse way to declare credentials to inherit from the
service manager into a service. This option may be used multiple times, each
time defining an additional credential to pass to the unit.
If an absolute path referring to a directory is specified, every file in that
directory (recursively) will be loaded as a separate credential. The ID for
each credential will be the provided ID suffixed with "_$FILENAME"
(e.g., "Key_file1"). When loading from a directory, symlinks will be
ignored.
The contents of the file/socket may be arbitrary binary or textual data,
including newline characters and NUL bytes.
The LoadCredentialEncrypted= setting is identical to
LoadCredential=, except that the credential data is decrypted and
authenticated before being passed on to the executed processes. Specifically,
the referenced path should refer to a file or socket with an encrypted
credential, as implemented by systemd-creds(1). This credential is
loaded, decrypted, authenticated and then passed to the application in
plaintext form, in the same way a regular credential specified via
LoadCredential= would be. A credential configured this way may be
symmetrically encrypted/authenticated with a secret key derived from the
system's TPM2 security chip, or with a secret key stored in
/var/lib/systemd/credentials.secret, or with both. Using encrypted and
authenticated credentials improves security as credentials are not stored in
plaintext and only authenticated and decrypted into plaintext the moment a
service requiring them is started. Moreover, credentials may be bound to the
local hardware and installations, so that they cannot easily be analyzed
offline, or be generated externally. When DevicePolicy= is set to
"closed" or "strict", or set to "auto" and
DeviceAllow= is set, or PrivateDevices= is set, then this
setting adds /dev/tpmrm0 with rw mode to DeviceAllow=. See
systemd.resource-control(5) for the details about DevicePolicy=
or DeviceAllow=.
The credential files/IPC sockets must be accessible to the service manager, but
don't have to be directly accessible to the unit's processes: the credential
data is read and copied into separate, read-only copies for the unit that are
accessible to appropriately privileged processes. This is particularly useful
in combination with DynamicUser= as this way privileged data can be
made available to processes running under a dynamic UID (i.e. not a previously
known one) without having to open up access to all users.
In order to reference the path a credential may be read from within a
ExecStart= command line use
"${CREDENTIALS_DIRECTORY}/mycred", e.g. "ExecStart=cat
${CREDENTIALS_DIRECTORY}/mycred". In order to reference the path a
credential may be read from within a Environment= line use
"%d/mycred", e.g. "Environment=MYCREDPATH=%d/mycred". For
system services the path may also be referenced as "/run/credentials/
UNITNAME" in cases where no interpolation is possible, e.g.
configuration files of software that does not yet support credentials
natively. $CREDENTIALS_DIRECTORY is considered the primary interface to
look for credentials, though, since it also works for user services.
Currently, an accumulated credential size limit of 1 MB per unit is enforced.
The service manager itself may receive system credentials that can be propagated
to services from a hosting container manager or VM hypervisor. See the
Container Interface[14] documentation for details about the former. For
the latter, pass DMI/SMBIOS[15] OEM string table entries (field type
11) with a prefix of "io.systemd.credential:" or
"io.systemd.credential.binary:". In both cases a key/value pair
separated by "=" is expected, in the latter case the right-hand side
is Base64 decoded when parsed (thus permitting binary data to be passed in).
Example qemu switch: "-smbios
type=11,value=io.systemd.credential:xx=yy", or "-smbios
type=11,value=io.systemd.credential.binary:rick=TmV2ZXIgR29ubmEgR2l2ZSBZb3UgVXA=".
Alternatively, use the qemu "fw_cfg" node
"opt/io.systemd.credentials/". Example qemu switch: "-fw_cfg
name=opt/io.systemd.credentials/mycred,string=supersecret". They may also
be specified on the kernel command line using the
"systemd.set_credential=" switch (see systemd(1)) and from
the UEFI firmware environment via systemd-stub(7).
If referencing an AF_UNIX stream socket to connect to, the connection
will originate from an abstract namespace socket, that includes information
about the unit and the credential ID in its socket name. Use
getpeername(2) to query this information. The returned socket name is
formatted as NUL RANDOM "/unit/" UNIT
"/" ID, i.e. a NUL byte (as required for abstract
namespace socket names), followed by a random string (consisting of
alphadecimal characters), followed by the literal string "/unit/",
followed by the requesting unit name, followed by the literal character
"/", followed by the textual credential ID requested. Example:
"\0adf9d86b6eda275e/unit/foobar.service/credx" in case the
credential "credx" is requested for a unit
"foobar.service". This functionality is useful for using a single
listening socket to serve credentials to multiple consumers.
For further information see System and Service Credentials[16]
documentation.
SetCredential=ID:VALUE,
SetCredentialEncrypted=ID: VALUE
The SetCredential= setting is similar
to LoadCredential= but accepts a literal value to use as data for the
credential, instead of a file system path to read the data from. Do not use
this option for data that is supposed to be secret, as it is accessible to
unprivileged processes via IPC. It's only safe to use this for user IDs,
public key material and similar non-sensitive data. For everything else use
LoadCredential=. In order to embed binary data into the credential data
use C-style escaping (i.e. "\n" to embed a newline, or
"\x00" to embed a NUL byte).
The SetCredentialEncrypted= setting is identical to SetCredential=
but expects an encrypted credential in literal form as value. This allows
embedding confidential credentials securely directly in unit files. Use
systemd-creds(1)' -p switch to generate suitable
SetCredentialEncrypted= lines directly from plaintext credentials. For
further details see LoadCredentialEncrypted= above.
If a credential of the same ID is listed in both LoadCredential= and
SetCredential=, the latter will act as default if the former cannot be
retrieved. In this case not being able to retrieve the credential from the
path specified in LoadCredential= is not considered fatal.
SYSTEM V COMPATIBILITY
UtmpIdentifier=Takes a four character identifier string for
an utmp(5) and wtmp entry for this service. This should only be set for
services such as getty implementations (such as agetty(8)) where
utmp/wtmp entries must be created and cleared before and after execution, or
for services that shall be executed as if they were run by a getty
process (see below). If the configured string is longer than four characters,
it is truncated and the terminal four characters are used. This setting
interprets %I style string replacements. This setting is unset by default,
i.e. no utmp/wtmp entries are created or cleaned up for this service.
UtmpMode=
Takes one of "init",
"login" or "user". If UtmpIdentifier= is set,
controls which type of utmp(5)/wtmp entries for this service are
generated. This setting has no effect unless UtmpIdentifier= is set
too. If "init" is set, only an INIT_PROCESS entry is
generated and the invoked process must implement a getty-compatible
utmp/wtmp logic. If "login" is set, first an INIT_PROCESS
entry, followed by a LOGIN_PROCESS entry is generated. In this case,
the invoked process must implement a login(1)-compatible utmp/wtmp
logic. If "user" is set, first an INIT_PROCESS entry, then a
LOGIN_PROCESS entry and finally a USER_PROCESS entry is
generated. In this case, the invoked process may be any process that is
suitable to be run as session leader. Defaults to "init".
ENVIRONMENT VARIABLES IN SPAWNED PROCESSES
Processes started by the service manager are executed with an environment variable block assembled from multiple sources. Processes started by the system service manager generally do not inherit environment variables set for the service manager itself (but this may be altered via PassEnvironment=), but processes started by the user service manager instances generally do inherit all environment variables set for the service manager itself. For each invoked process the list of environment variables set is compiled from the following sources:•Variables globally configured for the
service manager, using the DefaultEnvironment= setting in
systemd-system.conf(5), the kernel command line option
systemd.setenv= understood by systemd(1), or via
systemctl(1) set-environment verb.
•Variables defined by the service
manager itself (see the list below).
•Variables set in the service manager's
own environment variable block (subject to PassEnvironment= for the
system service manager).
•Variables set via Environment=
in the unit file.
•Variables read from files specified
via EnvironmentFile= in the unit file.
•Variables set by any PAM modules in
case PAMName= is in effect, cf. pam_env(8).
If the same environment variable is set by multiple of these sources, the later
source — according to the order of the list above — wins. Note
that as the final step all variables listed in UnsetEnvironment= are
removed from the compiled environment variable list, immediately before it is
passed to the executed process.
The general philosophy is to expose a small curated list of environment
variables to processes. Services started by the system manager (PID 1) will be
started, without additional service-specific configuration, with just a few
environment variables. The user manager inherits environment variables as any
other system service, but in addition may receive additional environment
variables from PAM, and, typically, additional imported variables when the
user starts a graphical session. It is recommended to keep the environment
blocks in both the system and user managers lean. Importing all variables
inherited by the graphical session or by one of the user shells is strongly
discouraged.
Hint: systemd-run -P env and systemd-run --user -P env print the
effective system and user service environment blocks.
Environment Variables Set or Propagated by the Service Manager
The following environment variables are propagated by the service manager or generated internally for each invoked process: $PATHColon-separated list of directories to use
when launching executables. systemd uses a fixed value of
"/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin" in the system
manager. When compiled for systems with "unmerged /usr/" (/bin is
not a symlink to /usr/bin), ":/sbin:/bin" is appended. In case of
the user manager, a different path may be configured by the distribution. It
is recommended to not rely on the order of entries, and have only one program
with a given name in $PATH.
$LANG
Locale. Can be set in locale.conf(5) or
on the kernel command line (see systemd(1) and
kernel-command-line(7)).
$USER, $LOGNAME, $HOME, $SHELL
User name (twice), home directory, and the
login shell. The variables are set for the units that have User= set,
which includes user systemd instances. See passwd(5).
$INVOCATION_ID
Contains a randomized, unique 128bit ID
identifying each runtime cycle of the unit, formatted as 32 character
hexadecimal string. A new ID is assigned each time the unit changes from an
inactive state into an activating or active state, and may be used to identify
this specific runtime cycle, in particular in data stored offline, such as the
journal. The same ID is passed to all processes run as part of the unit.
$XDG_RUNTIME_DIR
The directory to use for runtime objects (such
as IPC objects) and volatile state. Set for all services run by the user
systemd instance, as well as any system services that use
PAMName= with a PAM stack that includes pam_systemd. See below
and pam_systemd(8) for more information.
$RUNTIME_DIRECTORY, $STATE_DIRECTORY, $CACHE_DIRECTORY,
$LOGS_DIRECTORY, $CONFIGURATION_DIRECTORY
Absolute paths to the directories defined with
RuntimeDirectory=, StateDirectory=, CacheDirectory=,
LogsDirectory=, and ConfigurationDirectory= when those settings
are used.
$CREDENTIALS_DIRECTORY
An absolute path to the per-unit directory
with credentials configured via LoadCredential=/SetCredential=.
The directory is marked read-only and is placed in unswappable memory (if
supported and permitted), and is only accessible to the UID associated with
the unit via User= or DynamicUser= (and the superuser).
$MAINPID
The PID of the unit's main process if it is
known. This is only set for control processes as invoked by ExecReload=
and similar.
$MANAGERPID
The PID of the user systemd instance,
set for processes spawned by it.
$LISTEN_FDS, $LISTEN_PID, $LISTEN_FDNAMES
Information about file descriptors passed to a
service for socket activation. See sd_listen_fds(3).
$NOTIFY_SOCKET
The socket sd_notify() talks to. See
sd_notify(3).
$WATCHDOG_PID, $WATCHDOG_USEC
Information about watchdog keep-alive
notifications. See sd_watchdog_enabled(3).
$SYSTEMD_EXEC_PID
The PID of the unit process (e.g. process
invoked by ExecStart=). The child process can use this information to
determine whether the process is directly invoked by the service manager or
indirectly as a child of another process by comparing this value with the
current PID (similarly to the scheme used in sd_listen_fds(3) with
$LISTEN_PID and $LISTEN_FDS).
$TERM
Terminal type, set only for units connected to
a terminal ( StandardInput=tty, StandardOutput=tty, or
StandardError=tty). See termcap(5).
$LOG_NAMESPACE
Contains the name of the selected logging
namespace when the LogNamespace= service setting is used.
$JOURNAL_STREAM
If the standard output or standard error
output of the executed processes are connected to the journal (for example, by
setting StandardError=journal) $JOURNAL_STREAM contains the
device and inode numbers of the connection file descriptor, formatted in
decimal, separated by a colon (":"). This permits invoked processes
to safely detect whether their standard output or standard error output are
connected to the journal. The device and inode numbers of the file descriptors
should be compared with the values set in the environment variable to
determine whether the process output is still connected to the journal. Note
that it is generally not sufficient to only check whether
$JOURNAL_STREAM is set at all as services might invoke external
processes replacing their standard output or standard error output, without
unsetting the environment variable.
If both standard output and standard error of the executed processes are
connected to the journal via a stream socket, this environment variable will
contain information about the standard error stream, as that's usually the
preferred destination for log data. (Note that typically the same stream is
used for both standard output and standard error, hence very likely the
environment variable contains device and inode information matching both
stream file descriptors.)
This environment variable is primarily useful to allow services to optionally
upgrade their used log protocol to the native journal protocol (using
sd_journal_print(3) and other functions) if their standard output or
standard error output is connected to the journal anyway, thus enabling
delivery of structured metadata along with logged messages.
$SERVICE_RESULT
Only used for the service unit type. This
environment variable is passed to all ExecStop= and
ExecStopPost= processes, and encodes the service "result".
Currently, the following values are defined:
Table 5. Defined $SERVICE_RESULT values
This environment variable is useful to monitor failure or successful termination
of a service. Even though this variable is available in both
ExecStop= and ExecStopPost=, it is usually a better choice to
place monitoring tools in the latter, as the former is only invoked for
services that managed to start up correctly, and the latter covers both
services that failed during their start-up and those which failed during their
runtime.
$EXIT_CODE, $EXIT_STATUS
Value | Meaning |
"success" | The service ran successfully and exited cleanly. |
"protocol" | A protocol violation occurred: the service did not take the steps required by its unit configuration (specifically what is configured in its Type= setting). |
"timeout" | One of the steps timed out. |
"exit-code" | Service process exited with a non-zero exit code; see $EXIT_CODE below for the actual exit code returned. |
"signal" | A service process was terminated abnormally by a signal, without dumping core. See $EXIT_CODE below for the actual signal causing the termination. |
"core-dump" | A service process terminated abnormally with a signal and dumped core. See $EXIT_CODE below for the signal causing the termination. |
"watchdog" | Watchdog keep-alive ping was enabled for the service, but the deadline was missed. |
"start-limit-hit" | A start limit was defined for the unit and it was hit, causing the unit to fail to start. See systemd.unit(5)'s StartLimitIntervalSec= and StartLimitBurst= for details. |
"resources" | A catch-all condition in case a system operation failed. |
Only defined for the service unit type. These
environment variables are passed to all ExecStop=, ExecStopPost=
processes and contain exit status/code information of the main process of the
service. For the precise definition of the exit code and status, see
wait(2). $EXIT_CODE is one of "exited",
"killed", "dumped". $EXIT_STATUS contains the
numeric exit code formatted as string if $EXIT_CODE is
"exited", and the signal name in all other cases. Note that these
environment variables are only set if the service manager succeeded to start
and identify the main process of the service.
Table 6. Summary of possible service result variable values
$MONITOR_SERVICE_RESULT, $MONITOR_EXIT_CODE,
$MONITOR_EXIT_STATUS, $MONITOR_INVOCATION_ID,
$MONITOR_UNIT
$SERVICE_RESULT | $EXIT_CODE | $EXIT_STATUS |
"success" | "killed" | "HUP", "INT", "TERM", "PIPE" |
"exited" | "0" | |
"protocol" | not set | not set |
"exited" | "0" | |
"timeout" | "killed" | "TERM", "KILL" |
"exited" | "0", "1", "2", "3", ..., "255" | |
"exit-code" | "exited" | "1", "2", "3", ..., "255" |
"signal" | "killed" | "HUP", "INT", "KILL", ... |
"core-dump" | "dumped" | "ABRT", "SEGV", "QUIT", ... |
"watchdog" | "dumped" | "ABRT" |
"killed" | "TERM", "KILL" | |
"exited" | "0", "1", "2", "3", ..., "255" | |
"exec-condition" | "exited" | "1", "2", "3", "4", ..., "254" |
"oom-kill" | "killed" | "TERM", "KILL" |
"start-limit-hit" | not set | not set |
"resources" | any of the above | any of the above |
Note: the process may be also terminated by a signal not sent by systemd. In particular the process may send an arbitrary signal to itself in a handler for any of the non-maskable signals. Nevertheless, in the "timeout" and "watchdog" rows above only the signals that systemd sends have been included. Moreover, using SuccessExitStatus= additional exit statuses may be declared to indicate clean termination, which is not reflected by this table. |
Only defined for the service unit type. Those
environment variables are passed to all ExecStart= and
ExecStartPre= processes which run in services triggered by
OnFailure= or OnSuccess= dependencies.
Variables $MONITOR_SERVICE_RESULT, $MONITOR_EXIT_CODE and
$MONITOR_EXIT_STATUS take the same values as for ExecStop= and
ExecStopPost= processes. Variables $MONITOR_INVOCATION_ID and
$MONITOR_UNIT are set to the invocation id and unit name of the service
which triggered the dependency.
Note that when multiple services trigger the same unit, those variables will be
not be passed. Consider using a template handler unit for that case
instead: "OnFailure= handler@%n.service" for non-templated
units, or "OnFailure= handler@%p-%i.service" for templated
units.
$PIDFILE
The path to the configured PID file, in case
the process is forked off on behalf of a service that uses the PIDFile=
setting, see systemd.service(5) for details. Service code may use this
environment variable to automatically generate a PID file at the location
configured in the unit file. This field is set to an absolute path in the file
system.
$TRIGGER_UNIT, $TRIGGER_PATH, $TRIGGER_TIMER_REALTIME_USEC,
$TRIGGER_TIMER_MONOTONIC_USEC
If the unit was activated dynamically (e.g.: a
corresponding path unit or timer unit), the unit that triggered it and other
type-dependent information will be passed via these variables. Note that this
information is provided in a best-effort way. For example, multiple triggers
happening one after another will be coalesced and only one will be reported,
with no guarantee as to which one it will be. Because of this, in most cases
this variable will be primarily informational, i.e. useful for debugging
purposes, is lossy, and should not be relied upon to propagate a comprehensive
reason for activation.
For system services, when PAMName= is enabled and pam_systemd is
part of the selected PAM stack, additional environment variables defined by
systemd may be set for services. Specifically, these are $XDG_SEAT,
$XDG_VTNR, see pam_systemd(8) for details.
PROCESS EXIT CODES
When invoking a unit process the service manager possibly fails to apply the execution parameters configured with the settings above. In that case the already created service process will exit with a non-zero exit code before the configured command line is executed. (Or in other words, the child process possibly exits with these error codes, after having been created by the fork(2) system call, but before the matching execve(2) system call is called.) Specifically, exit codes defined by the C library, by the LSB specification and by the systemd service manager itself are used. The following basic service exit codes are defined by the C library.Exit Code | Symbolic Name | Description |
0 | EXIT_SUCCESS | Generic success code. |
1 | EXIT_FAILURE | Generic failure or unspecified error. |
Exit Code | Symbolic Name | Description |
2 | EXIT_INVALIDARGUMENT | Invalid or excess arguments. |
3 | EXIT_NOTIMPLEMENTED | Unimplemented feature. |
4 | EXIT_NOPERMISSION | The user has insufficient privileges. |
5 | EXIT_NOTINSTALLED | The program is not installed. |
6 | EXIT_NOTCONFIGURED | The program is not configured. |
7 | EXIT_NOTRUNNING | The program is not running. |
Exit Code | Symbolic Name | Description |
200 | EXIT_CHDIR | Changing to the requested working directory failed. See WorkingDirectory= above. |
201 | EXIT_NICE | Failed to set up process scheduling priority (nice level). See Nice= above. |
202 | EXIT_FDS | Failed to close unwanted file descriptors, or to adjust passed file descriptors. |
203 | EXIT_EXEC | The actual process execution failed (specifically, the execve(2) system call). Most likely this is caused by a missing or non-accessible executable file. |
204 | EXIT_MEMORY | Failed to perform an action due to memory shortage. |
205 | EXIT_LIMITS | Failed to adjust resource limits. See LimitCPU= and related settings above. |
206 | EXIT_OOM_ADJUST | Failed to adjust the OOM setting. See OOMScoreAdjust= above. |
207 | EXIT_SIGNAL_MASK | Failed to set process signal mask. |
208 | EXIT_STDIN | Failed to set up standard input. See StandardInput= above. |
209 | EXIT_STDOUT | Failed to set up standard output. See StandardOutput= above. |
210 | EXIT_CHROOT | Failed to change root directory (chroot(2)). See RootDirectory=/ RootImage= above. |
211 | EXIT_IOPRIO | Failed to set up IO scheduling priority. See IOSchedulingClass=/IOSchedulingPriority= above. |
212 | EXIT_TIMERSLACK | Failed to set up timer slack. See TimerSlackNSec= above. |
213 | EXIT_SECUREBITS | Failed to set process secure bits. See SecureBits= above. |
214 | EXIT_SETSCHEDULER | Failed to set up CPU scheduling. See CPUSchedulingPolicy=/CPUSchedulingPriority= above. |
215 | EXIT_CPUAFFINITY | Failed to set up CPU affinity. See CPUAffinity= above. |
216 | EXIT_GROUP | Failed to determine or change group credentials. See Group=/SupplementaryGroups= above. |
217 | EXIT_USER | Failed to determine or change user credentials, or to set up user namespacing. See User=/PrivateUsers= above. |
218 | EXIT_CAPABILITIES | Failed to drop capabilities, or apply ambient capabilities. See CapabilityBoundingSet=/ AmbientCapabilities= above. |
219 | EXIT_CGROUP | Setting up the service control group failed. |
220 | EXIT_SETSID | Failed to create new process session. |
221 | EXIT_CONFIRM | Execution has been cancelled by the user. See the systemd.confirm_spawn= kernel command line setting on kernel-command-line(7) for details. |
222 | EXIT_STDERR | Failed to set up standard error output. See StandardError= above. |
224 | EXIT_PAM | Failed to set up PAM session. See PAMName= above. |
225 | EXIT_NETWORK | Failed to set up network namespacing. See PrivateNetwork= above. |
226 | EXIT_NAMESPACE | Failed to set up mount, UTS, or IPC namespacing. See ReadOnlyPaths=, ProtectHostname=, PrivateIPC=, and related settings above. |
227 | EXIT_NO_NEW_PRIVILEGES | Failed to disable new privileges. See NoNewPrivileges=yes above. |
228 | EXIT_SECCOMP | Failed to apply system call filters. See SystemCallFilter= and related settings above. |
229 | EXIT_SELINUX_CONTEXT | Determining or changing SELinux context failed. See SELinuxContext= above. |
230 | EXIT_PERSONALITY | Failed to set up an execution domain (personality). See Personality= above. |
231 | EXIT_APPARMOR_PROFILE | Failed to prepare changing AppArmor profile. See AppArmorProfile= above. |
232 | EXIT_ADDRESS_FAMILIES | Failed to restrict address families. See RestrictAddressFamilies= above. |
233 | EXIT_RUNTIME_DIRECTORY | Setting up runtime directory failed. See RuntimeDirectory= and related settings above. |
235 | EXIT_CHOWN | Failed to adjust socket ownership. Used for socket units only. |
236 | EXIT_SMACK_PROCESS_LABEL | Failed to set SMACK label. See SmackProcessLabel= above. |
237 | EXIT_KEYRING | Failed to set up kernel keyring. |
238 | EXIT_STATE_DIRECTORY | Failed to set up unit's state directory. See StateDirectory= above. |
239 | EXIT_CACHE_DIRECTORY | Failed to set up unit's cache directory. See CacheDirectory= above. |
240 | EXIT_LOGS_DIRECTORY | Failed to set up unit's logging directory. See LogsDirectory= above. |
241 | EXIT_CONFIGURATION_DIRECTORY | Failed to set up unit's configuration directory. See ConfigurationDirectory= above. |
242 | EXIT_NUMA_POLICY | Failed to set up unit's NUMA memory policy. See NUMAPolicy= and NUMAMask= above. |
243 | EXIT_CREDENTIALS | Failed to set up unit's credentials. See LoadCredential= and SetCredential= above. |
245 | EXIT_BPF | Failed to apply BPF restrictions. See RestrictFileSystems= above. |
Exit Code | Symbolic Name | Description |
64 | EX_USAGE | Command line usage error |
65 | EX_DATAERR | Data format error |
66 | EX_NOINPUT | Cannot open input |
67 | EX_NOUSER | Addressee unknown |
68 | EX_NOHOST | Host name unknown |
69 | EX_UNAVAILABLE | Service unavailable |
70 | EX_SOFTWARE | internal software error |
71 | EX_OSERR | System error (e.g., can't fork) |
72 | EX_OSFILE | Critical OS file missing |
73 | EX_CANTCREAT | Can't create (user) output file |
74 | EX_IOERR | Input/output error |
75 | EX_TEMPFAIL | Temporary failure; user is invited to retry |
76 | EX_PROTOCOL | Remote error in protocol |
77 | EX_NOPERM | Permission denied |
78 | EX_CONFIG | Configuration error |
EXAMPLES
Example 3. $MONITOR_* usage[Unit] Description=Service which can trigger an OnFailure= dependency OnFailure=myhandler.service [Service] ExecStart=/bin/myprogram
[Unit] Description=Service which can trigger an OnSuccess= dependency OnSuccess=myhandler.service [Service] ExecStart=/bin/mysecondprogram
[Unit] Description=Acts on service failing or succeeding [Service] ExecStart=/bin/bash -c "echo $MONITOR_SERVICE_RESULT $MONITOR_EXIT_CODE $MONITOR_EXIT_STATUS $MONITOR_INVOCATION_ID $MONITOR_UNIT"
MONITOR_SERVICE_RESULT=exit-code MONITOR_EXIT_CODE=exited MONITOR_EXIT_STATUS=1 MONITOR_INVOCATION_ID=cc8fdc149b2b4ca698d4f259f4054236 MONITOR_UNIT=myfailer.service
MONITOR_SERVICE_RESULT=success MONITOR_EXIT_CODE=exited MONITOR_EXIT_STATUS=0 MONITOR_INVOCATION_ID=6ab9af147b8c4a3ebe36e7a5f8611697 MONITOR_UNIT=mysuccess.service
SEE ALSO
systemd(1), systemctl(1), systemd-analyze(1), journalctl(1), systemd-system.conf(5), systemd.unit(5), systemd.service(5), systemd.socket(5), systemd.swap(5), systemd.mount(5), systemd.kill(5), systemd.resource-control(5), systemd.time(7), systemd.directives(7), tmpfiles.d(5), exec(3), fork(2)NOTES
- 1.
- Discoverable Partitions Specification
- 2.
- The /proc Filesystem
- 3.
- User/Group Name Syntax
- 4.
- No New Privileges Flag
- 5.
- JSON User Record
- 6.
- The /proc Filesystem
- 7.
- unicode scalar values
- 8.
- noncharacters
- 9.
- byte order mark
- 10.
- unquoted text
- 11.
- single-quoted text
- 12.
- double-quoted text
- 13.
- Base64
- 14.
- Container Interface
- 15.
- DMI/SMBIOS
- 16.
- System and Service Credentials
- 17.
- LSB specification
systemd 252 |