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.
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.
--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= is specified.FILE
-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.
--subsystem-match[=SUBSYSTEM], --subsystem-nomatch[=SUBSYSTEM]¶When used with --export-db, only show devices of or not of the given
subsystem respectively.
--attr-match[=FILE[=VALUE]], --attr-nomatch[=FILE[=VALUE]]¶When used with --export-db, only show devices matching or not matching the
given attribute respectively.
--property-match[=KEY=VALUE]¶When used with --export-db, only show devices matching the given property
and value.
--tag-match[=TAG]¶When used with --export-db, only show devices with the given tag.
--sysname-match[=NAME]¶When used with --export-db, only show devices with the given
"/sys" path.
--name-match[=NAME]¶When used with --export-db, only show devices with the given name in
"/dev".
--parent-match[=NAME]¶When used with --export-db, only show devices with the given parent
device.
--initialized-match, --initialized-nomatch¶When used with --export-db, only show devices that are initialized or not
initialized respectively.
--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¶--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 |
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.
-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 invoking udevadm control --ping before udevadm trigger.
-h, --help¶In addition, optional positional arguments can be used
to specify device names or sys paths. They must start with
/dev/ or /sys/
respectively.
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¶See systemd-udev-settle.service(8) for more information.
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.
-t, --timeout=seconds¶The maximum number of seconds to wait for a reply from systemd-udevd.
-h, --help¶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¶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.
-h, --help¶options]
[command]
[devpath|file|unit]
¶Run a built-in command COMMAND
for device DEVPATH, and print debug
output.
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.
--root=PATH¶When looking for udev rules files located in udev/rules.d directories,
operate on files underneath the specified root path PATH.
--no-summary¶Do not show summary.
--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.
-h, --help¶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".
--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¶options]
[command]
…
¶udevadm lock takes an (advisory) exclusive lock on a block device (or all specified devices), as per Locking Block Device Access 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.)
--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 number of --device= and
--backing= switches specified in case these resolve to the same "whole"
devices.
-h, --help¶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