NAME
udevadm - udev management toolSYNOPSIS
udevadm
[ --debug] [--version] [--help]
udevadm
info [options] [devpath]
udevadm
trigger [options] [devpath]
udevadm
settle [options]
udevadm
control option
udevadm
monitor [options]
udevadm
test [options] devpath
udevadm
test-builtin [options] command
devpath
udevadm
wait [options] device|syspath
udevadm
lock [options] command
DESCRIPTION
udevadm expects a command and command specific options. It controls the runtime behavior of systemd-udevd, requests kernel events, manages the event queue, and provides simple debugging mechanisms.OPTIONS
-d, --debugPrint debug messages to standard error. This
option is implied in udevadm test and udevadm test-builtin
commands.
-h, --help
Print a short help text and exit.
udevadm info [ options] [devpath|file|unit...]
Query the udev database for device information. Positional arguments should be used to specify one or more devices. Each one may be a device name (in which case it must start with /dev/), a sys path (in which case it must start with /sys/), or a systemd device unit name (in which case it must end with ".device", see systemd.device(5)). -q, --query=TYPEQuery the database for the specified type of
device data. Valid TYPEs are: name, symlink, path,
property, all.
--property=NAME
When showing device properties using the
--query=property option, limit display to properties specified in the
argument. The argument should be a comma-separated list of property names. If
not specified, all known properties are shown.
--value
When showing device properties using the
--query=property option, print only their values, and skip the property
name and "=".
Cannot be used together with -x/--export or
-P/--export-prefix.
-p, --path=DEVPATH
The /sys/ path of the device to query, e.g.
[/sys/]/class/block/sda. This option is an alternative to the positional
argument with a /sys/ prefix. udevadm info --path=/class/block/sda is
equivalent to udevadm info /sys/class/block/sda.
-n, --name=FILE
The name of the device node or a symlink to
query, e.g. [/dev/]/sda. This option is an alternative to the positional
argument with a /dev/ prefix. udevadm info --name=sda is equivalent to
udevadm info /dev/sda.
-r, --root
Print absolute paths in name or
symlink query.
-a, --attribute-walk
Print all sysfs properties of the specified
device that can be used in udev rules to match the specified device. It prints
all devices along the chain, up to the root of sysfs that can be used in udev
rules.
-t, --tree
Display a sysfs tree. This recursively
iterates through the sysfs hierarchy and displays it in a tree structure. If a
path is specified only the subtree below and its parent directories are shown.
This will show both device and subsystem items.
-x, --export
Print output as key/value pairs. Values are
enclosed in single quotes. This takes effects only when
--query=property or --device-id-of-file=FILE is
specified.
-P, --export-prefix=NAME
Add a prefix to the key name of exported
values. This implies --export.
-d, --device-id-of-file=FILE
Print major/minor numbers of the underlying
device, where the file lives on. If this is specified, all positional
arguments are ignored.
-e, --export-db
Export the content of the udev database.
-c, --cleanup-db
Cleanup the udev database.
-w[SECONDS], --wait-for-initialization[=SECONDS]
Wait for device to be initialized. If argument
SECONDS is not specified, the default is to wait forever.
-h, --help
Print a short help text and exit.
--no-pager
Do not pipe output into a pager.
The generated output shows the current device database entry in a terse format.
Each line shown is prefixed with one of the following characters:
Prefix | Meaning |
"P:" | Device path in /sys/ |
"M:" | Device name in /sys/ (i.e. the last component of "P:") |
"R:" | Device number in /sys/ (i.e. the numeric suffix of the last component of "P:") |
"U:" | Kernel subsystem |
"T:" | Kernel device type within subsystem |
"D:" | Kernel device node major/minor |
"I:" | Network interface index |
"N:" | Kernel device node name |
"L:" | Device node symlink priority |
"S:" | Device node symlink |
"Q:" | Block device sequence number (DISKSEQ) |
"V:" | Attached driver |
"E:" | Device property |
udevadm trigger [ options] [devpath|file|unit]
Request device events from the kernel. Primarily used to replay events at system coldplug time.Print the list of devices which will be
triggered.
-n, --dry-run
Do not actually trigger the event.
-q, --quiet
Suppress error logging in triggering
events.
-t, --type=TYPE
Trigger a specific type of devices. Valid
types are "all", "devices", and "subsystems".
The default value is "devices".
-c, --action=ACTION
Type of event to be triggered. Possible
actions are "add", "remove", "change",
"move", "online", "offline", "bind",
and "unbind". Also, the special value "help" can be used
to list the possible actions. The default value is "change".
--prioritized-subsystem=SUBSYSTEM[,SUBSYSTEM...]
Takes a comma separated list of subsystems.
When triggering events for devices, the devices from the specified subsystems
and their parents are triggered first. For example, if
--prioritized-subsystem=block,net, then firstly all block devices and
their parents are triggered, in the next all network devices and their parents
are triggered, and lastly the other devices are triggered. This option can be
specified multiple times, and in that case the lists of the subsystems will be
merged. That is, --prioritized-subsystem=block
--prioritized-subsystem=net is equivalent to
--prioritized-subsystem=block,net.
-s, --subsystem-match=SUBSYSTEM
Trigger events for devices which belong to a
matching subsystem. This option supports shell style pattern matching. When
this option is specified more than once, then each matching result is ORed,
that is, all the devices in each subsystem are triggered.
-S, --subsystem-nomatch=SUBSYSTEM
Do not trigger events for devices which belong
to a matching subsystem. This option supports shell style pattern matching.
When this option is specified more than once, then each matching result is
ANDed, that is, devices which do not match all specified subsystems are
triggered.
-a,
--attr-match=ATTRIBUTE=VALUE
Trigger events for devices with a matching
sysfs attribute. If a value is specified along with the attribute name, the
content of the attribute is matched against the given value using shell style
pattern matching. If no value is specified, the existence of the sysfs
attribute is checked. When this option is specified multiple times, then each
matching result is ANDed, that is, only devices which have all specified
attributes are triggered.
-A,
--attr-nomatch=ATTRIBUTE=VALUE
Do not trigger events for devices with a
matching sysfs attribute. If a value is specified along with the attribute
name, the content of the attribute is matched against the given value using
shell style pattern matching. If no value is specified, the existence of the
sysfs attribute is checked. When this option is specified multiple times, then
each matching result is ANDed, that is, only devices which have none of the
specified attributes are triggered.
-p,
--property-match=PROPERTY=VALUE
Trigger events for devices with a matching
property value. This option supports shell style pattern matching. When this
option is specified more than once, then each matching result is ORed, that
is, devices which have one of the specified properties are triggered.
-g, --tag-match=TAG
Trigger events for devices with a matching
tag. When this option is specified multiple times, then each matching result
is ANDed, that is, devices which have all specified tags are triggered.
-y, --sysname-match=NAME
Trigger events for devices for which the last
component (i.e. the filename) of the /sys/ path matches the specified
PATH. This option supports shell style pattern matching. When this
option is specified more than once, then each matching result is ORed, that
is, all devices which have any of the specified NAME are
triggered.
--name-match=NAME
Trigger events for devices with a matching
device path. When this option is specified more than once, then each matching
result is ORed, that is, all specified devices are triggered.
-b, --parent-match=SYSPATH
Trigger events for all children of a given
device. When this option is specified more than once, then each matching
result is ORed, that is, all children of each specified device are
triggered.
--initialized-match, --initialized-nomatch
When --initialized-match is specified,
trigger events for devices that are already initialized by
systemd-udevd, and skip devices that are not initialized yet.
When --initialized-nomatch is specified, trigger events for devices that
are not initialized by systemd-udevd yet, and skip devices that are
already initialized.
Typically, it is essential that applications which intend to use such a match,
make sure a suitable udev rule is installed that sets at least one property on
devices that shall be matched. See also Initialized Devices section below for
more details.
WARNING: --initialized-nomatch can potentially save a significant amount
of time compared to re-triggering all devices in the system and e.g. can be
used to optimize boot time. However, this is not safe to be used in a boot
sequence in general. Especially, when udev rules for a device depend on its
parent devices (e.g. "ATTRS" or "IMPORT{parent}" keys, see
udev(7) for more details), the final state of the device becomes easily
unstable with this option.
-w, --settle
Apart from triggering events, also waits for
those events to finish. Note that this is different from calling udevadm
settle. udevadm settle waits for all events to finish. This option
only waits for events triggered by the same command to finish.
--uuid
Trigger the synthetic device events, and
associate a randomized UUID with each. These UUIDs are printed to standard
output, one line for each event. These UUIDs are included in the uevent
environment block (in the "SYNTH_UUID=" property) and may be used to
track delivery of the generated events.
--wait-daemon[=SECONDS]
Before triggering uevents, wait for
systemd-udevd daemon to be initialized. Optionally takes timeout value.
Default timeout is 5 seconds. This is equivalent to invoke invoking udevadm
control --ping before udevadm trigger.
-h, --help
Print a short help text and exit.
In addition, optional positional arguments can be used to specify device names
or sys paths. They must start with /dev/ or /sys/ respectively.
udevadm settle [ options]
Watches the udev event queue, and exits if all current events are handled. -t, --timeout=SECONDSMaximum number of seconds to wait for the
event queue to become empty. The default value is 120 seconds. A value of 0
will check if the queue is empty and always return immediately. A non-zero
value will return an exit code of 0 if queue became empty before timeout was
reached, non-zero otherwise.
-E, --exit-if-exists=FILE
Stop waiting if file exists.
-h, --help
Print a short help text and exit.
See systemd-udev-settle.service(8) for more information.
udevadm control option
Modify the internal state of the running udev daemon. -e, --exitSignal and wait for systemd-udevd to exit. No
option except for --timeout can be specified after this option. Note
that systemd-udevd.service contains Restart=always and so as a result,
this option restarts systemd-udevd. If you want to stop systemd-udevd.service,
please use the following:
-l, --log-level=value
systemctl stop systemd-udevd-control.socket systemd-udevd-kernel.socket systemd-udevd.service
Set the internal log level of systemd-udevd.
Valid values are the numerical syslog priorities or their textual
representations: emerg, alert, crit, err,
warning, notice, info, and debug.
-s, --stop-exec-queue
Signal systemd-udevd to stop executing new
events. Incoming events will be queued.
-S, --start-exec-queue
Signal systemd-udevd to enable the execution
of events.
-R, --reload
Signal systemd-udevd to reload the rules files
and other databases like the kernel module index. Reloading rules and
databases does not apply any changes to already existing devices; the new
configuration will only be applied to new events.
-p, --property=KEY=value
Set a global property for all events.
-m, --children-max=value
Set the maximum number of events,
systemd-udevd will handle at the same time.
--ping
Send a ping message to systemd-udevd and wait
for the reply. This may be useful to check that systemd-udevd daemon is
running.
-t, --timeout=seconds
The maximum number of seconds to wait for a
reply from systemd-udevd.
-h, --help
Print a short help text and exit.
udevadm monitor [ options]
Listens to the kernel uevents and events sent out by a udev rule and prints the devpath of the event to the console. It can be used to analyze the event timing, by comparing the timestamps of the kernel uevent and the udev event. -k, --kernelPrint the kernel uevents.
-u, --udev
Print the udev event after the rule
processing.
-p, --property
Also print the properties of the event.
-s, --subsystem-match=string[/string]
Filter kernel uevents and udev events by
subsystem[/devtype]. Only events with a matching subsystem value will pass.
When this option is specified more than once, then each matching result is
ORed, that is, all devices in the specified subsystems are monitored.
-t, --tag-match=string
Filter udev events by tag. Only udev events
with a given tag attached will pass. When this option is specified more than
once, then each matching result is ORed, that is, devices which have one of
the specified tags are monitored.
-h, --help
Print a short help text and exit.
udevadm test [ options] [devpath|file|unit]
Simulate a udev event run for the given device, and print debug output. -a, --action=ACTIONType of event to be simulated. Possible
actions are "add", "remove", "change",
"move", "online", "offline", "bind",
and "unbind". Also, the special value "help" can be used
to list the possible actions. The default value is "add".
-N,
--resolve-names=early|late|never
Specify when udevadm should resolve names of
users and groups. When set to early (the default), names will be
resolved when the rules are parsed. When set to late, names will be
resolved for every event. When set to never, names will never be
resolved and all devices will be owned by root.
-h, --help
Print a short help text and exit.
udevadm test-builtin [ options] [command] [devpath|file|unit]
Run a built-in command COMMAND for device DEVPATH, and print debug output. -a, --action=ACTIONType of event to be simulated. Possible
actions are "add", "remove", "change",
"move", "online", "offline", "bind",
and "unbind". Also, the special value "help" can be used
to list the possible actions. The default value is "add".
-h, --help
Print a short help text and exit.
udevadm wait [ options] [device|syspath] ...
Wait for devices or device symlinks being created and initialized by systemd-udevd. Each device path must start with "/dev/" or "/sys/", e.g. "/dev/sda", "/dev/disk/by-path/pci-0000:3c:00.0-nvme-1-part1", "/sys/devices/pci0000:00/0000:00:1f.6/net/eth0", or "/sys/class/net/eth0". This can take multiple devices. This may be useful for waiting for devices being processed by systemd-udevd after e.g. partitioning or formatting the devices. -t, --timeout=SECONDSMaximum number of seconds to wait for the
specified devices or device symlinks being created, initialized, or removed.
The default value is "infinity".
--initialized=BOOL
Check if systemd-udevd initialized
devices. Defaults to true. When false, the command only checks if the
specified devices exist. Set false to this setting if there is no udev rules
for the specified devices, as the devices will never be considered as
initialized in that case. See Initialized Devices section below for more
details.
--removed
When specified, the command wait for devices
being removed instead of created or initialized. If this is specified,
--initialized= will be ignored.
--settle
When specified, also watches the udev event
queue, and wait for all queued events being processed by
systemd-udevd.
-h, --help
Print a short help text and exit.
udevadm lock [ options] [command] ...
udevadm lock takes an (advisory) exclusive lock on a block device (or all specified devices), as per Locking Block Device Access[1] and invokes a program with the locks taken. When the invoked program exits the locks are automatically released and its return value is propagated as exit code of udevadm lock. This tool is in particular useful to ensure that systemd-udevd.service(8) does not probe a block device while changes are made to it, for example partitions created or file systems formatted. Note that many tools that interface with block devices natively support taking relevant locks, see for example sfdisk(8)'s --lock switch. The command expects at least one block device specified via --device= or --backing=, and a command line to execute as arguments. --device=DEVICE, -d DEVICETakes a path to a device node of the device to
lock. This switch may be used multiple times (and in combination with
--backing=) in order to lock multiple devices. If a partition block
device node is specified the containing "whole" block device is
automatically determined and used for the lock, as per the specification. If
multiple devices are specified, they are deduplicated, sorted by the
major/minor of their device nodes and then locked in order.
This switch must be used at least once, to specify at least one device to lock.
(Alternatively, use --backing=, see below.)
--backing=PATH, -b PATH
If a path to a device node is specified,
identical to --device=. However, this switch alternatively accepts a
path to a regular file or directory, in which case the block device of the
file system the file/directory resides on is automatically determined and used
as if it was specified with --device=.
--timeout=SECS, -t SECS
Specifies how long to wait at most until all
locks can be taken. Takes a value in seconds, or in the usual supported time
units, see systemd.time(7). If specified as zero the lock is attempted
and if not successful the invocation will immediately fail. If passed as
"infinity" (the default) the invocation will wait indefinitely until
the lock can be acquired. If the lock cannot be taken in the specified time
the specified command will not be executed and the invocation will fail.
--print, -p
Instead of locking the specified devices and
executing a command, just print the device paths that would be locked, and
execute no command. This command is useful to determine the "whole"
block device in case a partition block device is specified. The devices will
be sorted by their device node major number as primary ordering key and the
minor number as secondary ordering key (i.e. they are shown in the order
they'd be locked). Note that the number of lines printed here can be less than
the the number of --device= and --backing= switches specified in
case these resolve to the same "whole" devices.
-h, --help
Print a short help text and exit.
INITIALIZED DEVICES
Initialized devices are those for which at least one udev rule already completed execution – for any action but "remove" — that set a property or other device setting (and thus has an entry in the udev device database). Devices are no longer considered initialized if a "remove" action is seen for them (which removes their entry in the udev device database). Note that devices that have no udev rules are never considered initialized, but might still be announced via the sd-device API (or similar).EXAMPLE
Example 1. Format a File System Take a lock on the backing block device while creating a file system, to ensure that systemd-udevd doesn't probe or announce the new superblock before it is comprehensively written:# udevadm lock --device=/dev/sda1 mkfs.ext4 /dev/sda1
# udevadm lock --device=/dev/sda1 --device=/dev/sdb1 mkfs.btrfs /dev/sda1 /dev/sdb1
# udevadm lock -d /dev/sda1 dd if=fs.raw of=/dev/sda1
SEE ALSO
udev(7), systemd-udevd.service(8)NOTES
- 1.
- Locking Block Device Access
systemd 252 |