NAME
systemd.journal-fields - Special journal fieldsDESCRIPTION
Entries in the journal (as written by systemd-journald.service(8)) resemble a UNIX process environment block in syntax but with fields that may include binary data. Primarily, fields are formatted UTF-8 text strings, and binary encoding is used only where formatting as UTF-8 text strings makes little sense. New fields may freely be defined by applications, but a few fields have special meanings. All fields with special meanings are optional. In some cases, fields may appear more than once per entry.USER JOURNAL FIELDS
User fields are fields that are directly passed from clients and stored in the journal. MESSAGE=The human-readable message string for this
entry. This is supposed to be the primary text shown to the user. It is
usually not translated (but might be in some cases), and is not supposed to be
parsed for metadata.
MESSAGE_ID=
A 128-bit message identifier ID for
recognizing certain message types, if this is desirable. This should contain a
128-bit ID formatted as a lower-case hexadecimal string, without any
separating dashes or suchlike. This is recommended to be a UUID-compatible ID,
but this is not enforced, and formatted differently. Developers can generate a
new ID for this purpose with systemd-id128 new.
PRIORITY=
A priority value between 0 ("emerg")
and 7 ("debug") formatted as a decimal string. This field is
compatible with syslog's priority concept.
CODE_FILE=, CODE_LINE=, CODE_FUNC=
The code location generating this message, if
known. Contains the source filename, the line number and the function
name.
ERRNO=
The low-level Unix error number causing this
entry, if any. Contains the numeric value of errno(3) formatted as a
decimal string.
INVOCATION_ID=, USER_INVOCATION_ID=
A randomized, unique 128-bit ID identifying
each runtime cycle of the unit. This is different from
_SYSTEMD_INVOCATION_ID in that it is only used for messages coming from
systemd code (e.g. logs from the system/user manager or from forked processes
performing systemd-related setup).
SYSLOG_FACILITY=, SYSLOG_IDENTIFIER=, SYSLOG_PID=,
SYSLOG_TIMESTAMP=
Syslog compatibility fields containing the
facility (formatted as decimal string), the identifier string (i.e.
"tag"), the client PID, and the timestamp as specified in the
original datagram. (Note that the tag is usually derived from glibc's
program_invocation_short_name variable, see
program_invocation_short_name(3).)
Note that the journal service does not validate the values of any structured
journal fields whose name is not prefixed with an underscore, and this
includes any syslog related fields such as these. Hence, applications that
supply a facility, PID, or log level are expected to do so properly formatted,
i.e. as numeric integers formatted as decimal strings.
SYSLOG_RAW=
The original contents of the syslog line as
received in the syslog datagram. This field is only included if the
MESSAGE= field was modified compared to the original payload or the
timestamp could not be located properly and is not included in
SYSLOG_TIMESTAMP=. Message truncation occurs when the message contains
leading or trailing whitespace (trailing and leading whitespace is stripped),
or it contains an embedded NUL byte (the NUL byte and anything
after it is not included). Thus, the original syslog line is either stored as
SYSLOG_RAW= or it can be recreated based on the stored priority and
facility, timestamp, identifier, and the message payload in
MESSAGE=.
DOCUMENTATION=
A documentation URL with further information
about the topic of the log message. Tools such as journalctl will
include a hyperlink to an URL specified this way in their output. Should be an
"http://", "https://", "file:/",
"man:" or "info:" URL.
TID=
The numeric thread ID (TID) the log message
originates from.
UNIT=, USER_UNIT=
The name of a unit. Used by the system and
user managers when logging about specific units.
When --unit=name or --user-unit=name
are used with journalctl(1), a match pattern that includes "UNIT=
name.service" or "USER_UNIT= name.service" will
be generated.
TRUSTED JOURNAL FIELDS
Fields prefixed with an underscore are trusted fields, i.e. fields that are implicitly added by the journal and cannot be altered by client code. _PID=, _UID=, _GID=The process, user, and group ID of the process
the journal entry originates from formatted as a decimal string. Note that
entries obtained via "stdout" or "stderr" of forked
processes will contain credentials valid for a parent process (that initiated
the connection to systemd-journald).
_COMM=, _EXE=, _CMDLINE=
The name, the executable path, and the command
line of the process the journal entry originates from.
_CAP_EFFECTIVE=
The effective capabilities(7) of the
process the journal entry originates from.
_AUDIT_SESSION=, _AUDIT_LOGINUID=
The session and login UID of the process the
journal entry originates from, as maintained by the kernel audit
subsystem.
_SYSTEMD_CGROUP=, _SYSTEMD_SLICE=, _SYSTEMD_UNIT=,
_SYSTEMD_USER_UNIT=, _SYSTEMD_USER_SLICE=,
_SYSTEMD_SESSION=, _SYSTEMD_OWNER_UID=
The control group path in the systemd
hierarchy, the systemd slice unit name, the systemd unit name, the unit name
in the systemd user manager (if any), the systemd session ID (if any), and the
owner UID of the systemd user unit or systemd session (if any) of the process
the journal entry originates from.
_SELINUX_CONTEXT=
The SELinux security context (label) of the
process the journal entry originates from.
_SOURCE_REALTIME_TIMESTAMP=
The earliest trusted timestamp of the message,
if any is known that is different from the reception time of the journal. This
is the time in microseconds since the epoch UTC, formatted as a decimal
string.
_BOOT_ID=
The kernel boot ID for the boot the message
was generated in, formatted as a 128-bit hexadecimal string.
_MACHINE_ID=
The machine ID of the originating host, as
available in machine-id(5).
_SYSTEMD_INVOCATION_ID=
The invocation ID for the runtime cycle of the
unit the message was generated in, as available to processes of the unit in
$INVOCATION_ID (see systemd.exec(5)).
_HOSTNAME=
The name of the originating host.
_TRANSPORT=
How the entry was received by the journal
service. Valid transports are:
audit
_STREAM_ID=
for those read from the kernel audit
subsystem
driver
for internally generated messages
syslog
for those received via the local syslog socket
with the syslog protocol
journal
for those received via the native journal
protocol
stdout
for those read from a service's standard
output or error output
kernel
for those read from the kernel
Only applies to "_TRANSPORT=stdout"
records: specifies a randomized 128bit ID assigned to the stream connection
when it was first created. This ID is useful to reconstruct individual log
streams from the log records: all log records carrying the same stream ID
originate from the same stream.
_LINE_BREAK=
Only applies to "_TRANSPORT=stdout"
records: indicates that the log message in the standard output/error stream
was not terminated with a normal newline character ("\n", i.e. ASCII
10). Specifically, when set this field is one of nul (in case the line
was terminated by a NUL byte), line-max (in case the maximum log
line length was reached, as configured with LineMax= in
journald.conf(5)), eof (if this was the last log record of a
stream and the stream ended without a final newline character), or
pid-change (if the process which generated the log output changed in
the middle of a line). Note that this record is not generated when a normal
newline character was used for marking the log line end.
_NAMESPACE=
If this file was written by a
systemd-journald instance managing a journal namespace that is not the
default, this field contains the namespace identifier. See
systemd-journald.service(8) for details about journal namespaces.
_RUNTIME_SCOPE=
A string field that specifies the runtime
scope in which the message was logged. If "initrd", the log message
was processed while the system was running inside the initrd. If
"system", the log message was generated after the system switched
execution to the host root filesystem.
KERNEL JOURNAL FIELDS
Kernel fields are fields that are used by messages originating in the kernel and stored in the journal. _KERNEL_DEVICE=The kernel device name. If the entry is
associated to a block device, contains the major and minor numbers of the
device node, separated by ":" and prefixed by "b".
Similarly for character devices, but prefixed by "c". For network
devices, this is the interface index prefixed by "n". For all other
devices, this is the subsystem name prefixed by "+", followed by
":", followed by the kernel device name.
_KERNEL_SUBSYSTEM=
The kernel subsystem name.
_UDEV_SYSNAME=
The kernel device name as it shows up in the
device tree below /sys/.
_UDEV_DEVNODE=
The device node path of this device in
/dev/.
_UDEV_DEVLINK=
Additional symlink names pointing to the
device node in /dev/. This field is frequently set more than once per
entry.
FIELDS TO LOG ON BEHALF OF A DIFFERENT PROGRAM
Fields in this section are used by programs to specify that they are logging on behalf of another program or unit. Fields used by the systemd-coredump coredump kernel helper: COREDUMP_UNIT=, COREDUMP_USER_UNIT=Used to annotate messages containing coredumps
from system and session units. See coredumpctl(1).
Privileged programs (currently UID 0) may attach OBJECT_PID= to a
message. This will instruct systemd-journald to attach additional
fields on behalf of the caller:
OBJECT_PID=PID
PID of the program that this message pertains
to.
OBJECT_UID=, OBJECT_GID=, OBJECT_COMM=, OBJECT_EXE=,
OBJECT_CMDLINE=, OBJECT_AUDIT_SESSION=,
OBJECT_AUDIT_LOGINUID=, OBJECT_SYSTEMD_CGROUP=,
OBJECT_SYSTEMD_SESSION=, OBJECT_SYSTEMD_OWNER_UID=,
OBJECT_SYSTEMD_UNIT=, OBJECT_SYSTEMD_USER_UNIT=
These are additional fields added
automatically by systemd-journald. Their meaning is the same as
_UID=, _GID=, _COMM=, _EXE=, _CMDLINE=,
_AUDIT_SESSION=, _AUDIT_LOGINUID=, _SYSTEMD_CGROUP=,
_SYSTEMD_SESSION=, _SYSTEMD_UNIT=, _SYSTEMD_USER_UNIT=,
and _SYSTEMD_OWNER_UID= as described above, except that the process
identified by PID is described, instead of the process which logged the
message.
OBJECT_SYSTEMD_INVOCATION_ID=
An additional field added automatically by
systemd-journald. The meaning is mostly the same as
_SYSTEMD_INVOCATION_ID=, with the difference described above.
ADDRESS FIELDS
During serialization into external formats, such as the Journal Export Format[1] or the Journal JSON Format[2], the addresses of journal entries are serialized into fields prefixed with double underscores. Note that these are not proper fields when stored in the journal but for addressing metadata of entries. They cannot be written as part of structured log entries via calls such as sd_journal_send(3). They may also not be used as matches for sd_journal_add_match(3). __CURSOR=The cursor for the entry. A cursor is an
opaque text string that uniquely describes the position of an entry in the
journal and is portable across machines, platforms and journal files.
__REALTIME_TIMESTAMP=
The wallclock time (CLOCK_REALTIME) at
the point in time the entry was received by the journal, in microseconds since
the epoch UTC, formatted as a decimal string. This has different properties
from "_SOURCE_REALTIME_TIMESTAMP=", as it is usually a bit later but
more likely to be monotonic.
__MONOTONIC_TIMESTAMP=
The monotonic time (CLOCK_MONOTONIC) at
the point in time the entry was received by the journal in microseconds,
formatted as a decimal string. To be useful as an address for the entry, this
should be combined with the boot ID in "_BOOT_ID=".
SEE ALSO
systemd(1), systemd-journald.service(8), journalctl(1), journald.conf(5), sd-journal(3), coredumpctl(1), systemd.directives(7)NOTES
- 1.
- Journal Export Format
- 2.
- Journal JSON Format
systemd 252 |