udevadm(8) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | OPTIONS | INITIALIZED DEVICES | EXAMPLE | SEE ALSO | NOTES | COLOPHON

UDEVADM(8)                       udevadm                      UDEVADM(8)

NAME         top

       udevadm - udev management tool

SYNOPSIS         top


       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

DESCRIPTION         top

       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         top

       -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.

   udevadm 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         top

       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         top

       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

SEE ALSO         top

       udev(7), systemd-udevd.service(8)

NOTES         top

        1. Locking Block Device Access
           https://systemd.io/BLOCK_DEVICE_LOCKING

COLOPHON         top

       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
       man-pages@man7.org

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)