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NAME | SYNOPSIS | DESCRIPTION | OPTIONS | INITIALIZED DEVICES | EXAMPLE | SEE ALSO | NOTES | COLOPHON |
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UDEVADM(8) udevadm UDEVADM(8)
udevadm - udev management tool
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 verify [options...] [file...]
udevadm wait [options] device|syspath
udevadm lock [options] command
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.
-d, --debug
Print 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=TYPE
Query 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.
Added in version 250.
--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.
Added in version 250.
-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.
Added in version 251.
-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.
Added in version 243.
--subsystem-match[=SUBSYSTEM], --subsystem-nomatch[=SUBSYSTEM]
When used with --export-db, only show devices of or not of
the given subsystem respectively.
Added in version 255.
--attr-match[=FILE[=VALUE]], --attr-nomatch[=FILE[=VALUE]]
When used with --export-db, only show devices matching or not
matching the given attribute respectively.
Added in version 255.
--property-match[=KEY=VALUE]
When used with --export-db, only show devices matching the
given property and value.
Added in version 255.
--tag-match[=TAG]
When used with --export-db, only show devices with the given
tag.
Added in version 255.
--sysname-match[=NAME]
When used with --export-db, only show devices with the given
"/sys" path.
Added in version 255.
--name-match[=NAME]
When used with --export-db, only show devices with the given
name in "/dev".
Added in version 255.
--parent-match[=NAME]
When used with --export-db, only show devices with the given
parent device.
Added in version 255.
--initialized-match, --initialized-nomatch
When used with --export-db, only show devices that are
initialized or not initialized respectively.
Added in version 255.
--json=MODE
Shows output formatted as JSON. Expects one of "short" (for
the shortest possible output without any redundant whitespace
or line breaks), "pretty" (for a pretty version of the same,
with indentation and line breaks) or "off" (to turn off JSON
output, the default).
-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:
Table 1. udevadm info output prefixes
┌────────┬──────────────────────────┐
│ 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.
Takes device specifications as positional arguments. See the
description of info above.
-v, --verbose
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.
Added in version 248.
-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.
Added in version 251.
-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.
Added in version 218.
-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.
Added in version 251.
-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.
Added in version 238.
--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.
Added in version 249.
--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 invoking udevadm
control --ping before udevadm trigger.
Added in version 241.
-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=SECONDS
Maximum 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.
[1mudevadm control option
Modify the internal state of the running udev daemon.
-e, --exit
Signal 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:
systemctl stop systemd-udevd-control.socket systemd-udevd-kernel.socket systemd-udevd.service
-l, --log-level=value
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. When 0 is specified, then the maximum is
determined based on the system resources.
--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.
Added in version 241.
-t, --timeout=seconds
The maximum number of seconds to wait for a reply from
systemd-udevd.
--load-credentials
When specified, the following credentials are used when
passed in:
udev.conf.*
These credentials should contain valid udev.conf(5)
configuration data. From each matching credential a
separate file is created. Example: a passed credential
udev.conf.50-foobar will be copied into a configuration
file /run/udev/udev.conf.d/50-foobar.conf.
Added in version 256.
udev.rules.*
These credentials should contain valid udev(7) rules.
From each matching credential a separate file is created.
Example: a passed credential udev.rules.50-foobar will be
copied into a configuration file
/run/udev/rules.d/50-foobar.rules.
Added in version 256.
Note, this does not imply --reload option. So, if
systemd-udevd is already running, please consider to also
specify -reload to make the copied udev rules files used by
systemd-udevd.
Added in version 256.
-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, --kernel
Print 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=ACTION
Type 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.
Added in version 209.
-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=ACTION
Type 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".
Added in version 250.
-h, --help
Print a short help text and exit.
--version
Print a short version string and exit.
udevadm verify [options] [file] ...
Verify syntactic, semantic, and stylistic correctness of udev
rules files.
Positional arguments could be used to specify one or more files
to check. If no files are specified, the udev rules are read from
the files located in the same udev/rules.d directories that are
processed by the udev daemon.
The exit status is 0 if all specified udev rules files are
syntactically, semantically, and stylistically correct, and a
non-zero error code otherwise.
-N, --resolve-names=early|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 never, names
will never be resolved.
Added in version 254.
--root=PATH
When looking for udev rules files located in udev/rules.d
directories, operate on files underneath the specified root
path PATH.
Added in version 254.
--no-summary
Do not show summary.
Added in version 254.
--no-style
Ignore style issues. When specified, even if style issues are
found in udev rules files, the exit status is 0 if no
syntactic or semantic errors are found.
Added in version 254.
-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=SECONDS
Maximum number of seconds to wait for the specified devices
or device symlinks being created, initialized, or removed.
The default value is "infinity".
Added in version 251.
--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.
Added in version 251.
--removed
When specified, the command wait for devices being removed
instead of created or initialized. If this is specified,
--initialized= will be ignored.
Added in version 251.
--settle
When specified, also watches the udev event queue, and wait
for all queued events being processed by systemd-udevd.
Added in version 251.
-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 DEVICE
Takes 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.)
Added in version 251.
--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=.
Added in version 251.
--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.
Added in version 251.
--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 number of --device= and --backing=
switches specified in case these resolve to the same "whole"
devices.
Added in version 251.
-h, --help
Print a short help text and exit.
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 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
Example 2. Format a RAID File System
Similar, but take locks on multiple devices at once:
# udevadm lock --device=/dev/sda1 --device=/dev/sdb1 mkfs.btrfs /dev/sda1 /dev/sdb1
Example 3. Copy in a File System
Take a lock on the backing block device while copying in a
prepared file system image, to ensure that systemd-udevd doesn't
probe or announce the new superblock before it is fully written:
# udevadm lock -d /dev/sda1 dd if=fs.raw of=/dev/sda1
udev(7), systemd-udevd.service(8)
1. Locking Block Device Access
https://systemd.io/BLOCK_DEVICE_LOCKING
This page is part of the systemd (systemd system and service
manager) project. Information about the project can be found at
⟨http://www.freedesktop.org/wiki/Software/systemd⟩. If you have
a bug report for this manual page, see
⟨http://www.freedesktop.org/wiki/Software/systemd/#bugreports⟩.
This page was obtained from the project's upstream Git repository
⟨https://github.com/systemd/systemd.git⟩ on 2024-06-14. (At that
time, the date of the most recent commit that was found in the
repository was 2024-06-13.) If you discover any rendering
problems in this HTML version of the page, or you believe there
is a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
[email protected]
systemd 257~devel UDEVADM(8)
Pages that refer to this page: sd-device(3), iocost.conf(5), systemd.link(5), udev.conf(5), systemd.directives(7), systemd.index(7), systemd.net-naming-scheme(7), systemd.system-credentials(7), udev(7), dmsetup(8), lvmdump(8), systemd-udevd.service(8), systemd-udev-settle.service(8)
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