1UDEVADM(8) udevadm UDEVADM(8)
2
6 udevadm - udev management tool
7
9 udevadm [--debug] [--version] [--help]
10 udevadm info [options] [devpath]
12 udevadm trigger [options] [devpath]
14 udevadm settle [options]
16 udevadm control option
18 udevadm monitor [options]
20 udevadm test [options] devpath
22 udevadm test-builtin [options] command devpath
24 udevadm wait [options] device|syspath
26 udevadm lock [options] command
28
30 udevadm expects a command and command specific options. It controls the
31 runtime behavior of systemd-udevd, requests kernel events, manages the
32 event queue, and provides simple debugging mechanisms.
33
35 -d, --debug
36 Print debug messages to standard error. This option is implied in
37 udevadm test and udevadm test-builtin commands.
38 -h, --help
40 Print a short help text and exit.
41 udevadm info [options] [devpath|file|unit...]
43 Query the udev database for device information.
44 Positional arguments should be used to specify one or more devices.
46 Each one may be a device name (in which case it must start with /dev/),
47 a sys path (in which case it must start with /sys/), or a systemd
48 device unit name (in which case it must end with ".device", see
49 systemd.device(5)).
50 -q, --query=TYPE
52 Query the database for the specified type of device data. Valid
53 TYPEs are: name, symlink, path, property, all.
54 --property=NAME
56 When showing device properties using the --query=property option,
57 limit display to properties specified in the argument. The argument
58 should be a comma-separated list of property names. If not
59 specified, all known properties are shown.
60 --value
62 When showing device properties using the --query=property option,
63 print only their values, and skip the property name and "=".
64 Cannot be used together with -x/--export or -P/--export-prefix.
66 -p, --path=DEVPATH
68 The /sys/ path of the device to query, e.g.
69 [/sys/]/class/block/sda. This option is an alternative to the
70 positional argument with a /sys/ prefix. udevadm info
71 --path=/class/block/sda is equivalent to udevadm info
72 /sys/class/block/sda.
73 -n, --name=FILE
75 The name of the device node or a symlink to query, e.g.
76 [/dev/]/sda. This option is an alternative to the positional
77 argument with a /dev/ prefix. udevadm info --name=sda is
78 equivalent to udevadm info /dev/sda.
79 -r, --root
81 Print absolute paths in name or symlink query.
82 -a, --attribute-walk
84 Print all sysfs properties of the specified device that can be used
85 in udev rules to match the specified device. It prints all devices
86 along the chain, up to the root of sysfs that can be used in udev
87 rules.
88 -t, --tree
90 Display a sysfs tree. This recursively iterates through the sysfs
91 hierarchy and displays it in a tree structure. If a path is
92 specified only the subtree below and its parent directories are
93 shown. This will show both device and subsystem items.
94 -x, --export
96 Print output as key/value pairs. Values are enclosed in single
97 quotes. This takes effects only when --query=property or
98 --device-id-of-file=FILE is specified.
99 -P, --export-prefix=NAME
101 Add a prefix to the key name of exported values. This implies
102 --export.
103 -d, --device-id-of-file=FILE
105 Print major/minor numbers of the underlying device, where the file
106 lives on. If this is specified, all positional arguments are
107 ignored.
108 -e, --export-db
110 Export the content of the udev database.
111 -c, --cleanup-db
113 Cleanup the udev database.
114 -w[SECONDS], --wait-for-initialization[=SECONDS]
116 Wait for device to be initialized. If argument SECONDS is not
117 specified, the default is to wait forever.
118 -h, --help
120 Print a short help text and exit.
121 The generated output shows the current device database entry in a terse
123 format. Each line shown is prefixed with one of the following
124 characters:
125 Table 1. udevadm info output prefixes
127 ┌───────┬────────────────────────────┐
128 │Prefix │ Meaning │
129 ├───────┼────────────────────────────┤
130 │"P:" │ Device path in /sys/ │
131 ├───────┼────────────────────────────┤
132 │"M:" │ Device name in /sys/ (i.e. │
133 │ │ the last component of │
134 │ │ "P:") │
135 ├───────┼────────────────────────────┤
136 │"R:" │ Device number in /sys/ │
137 │ │ (i.e. the numeric suffix │
138 │ │ of the last component of │
139 │ │ "P:") │
140 ├───────┼────────────────────────────┤
141 │"U:" │ Kernel subsystem │
142 ├───────┼────────────────────────────┤
143 │"T:" │ Kernel device type within │
144 │ │ subsystem │
145 ├───────┼────────────────────────────┤
146 │"D:" │ Kernel device node │
147 │ │ major/minor │
148 ├───────┼────────────────────────────┤
149 │"I:" │ Network interface index │
150 ├───────┼────────────────────────────┤
151 │"N:" │ Kernel device node name │
152 ├───────┼────────────────────────────┤
153 │"L:" │ Device node symlink │
154 │ │ priority │
155 ├───────┼────────────────────────────┤
156 │"S:" │ Device node symlink │
157 ├───────┼────────────────────────────┤
158 │"Q:" │ Block device sequence │
159 │ │ number (DISKSEQ) │
160 ├───────┼────────────────────────────┤
161 │"V:" │ Attached driver │
162 ├───────┼────────────────────────────┤
163 │"E:" │ Device property │
164 └───────┴────────────────────────────┘
165 udevadm trigger [options] [devpath|file|unit]
167 Request device events from the kernel. Primarily used to replay events
168 at system coldplug time.
169 Takes device specifications as positional arguments. See the
171 description of info above.
172 -v, --verbose
174 Print the list of devices which will be triggered.
175 -n, --dry-run
177 Do not actually trigger the event.
178 -q, --quiet
180 Suppress error logging in triggering events.
181 -t, --type=TYPE
183 Trigger a specific type of devices. Valid types are "all",
184 "devices", and "subsystems". The default value is "devices".
185 -c, --action=ACTION
187 Type of event to be triggered. Possible actions are "add",
188 "remove", "change", "move", "online", "offline", "bind", and
189 "unbind". Also, the special value "help" can be used to list the
190 possible actions. The default value is "change".
191 --prioritized-subsystem=SUBSYSTEM[,SUBSYSTEM...]
193 Takes a comma separated list of subsystems. When triggering events
194 for devices, the devices from the specified subsystems and their
195 parents are triggered first. For example, if
196 --prioritized-subsystem=block,net, then firstly all block devices
197 and their parents are triggered, in the next all network devices
198 and their parents are triggered, and lastly the other devices are
199 triggered. This option can be specified multiple times, and in that
200 case the lists of the subsystems will be merged. That is,
201 --prioritized-subsystem=block --prioritized-subsystem=net is
202 equivalent to --prioritized-subsystem=block,net.
203 -s, --subsystem-match=SUBSYSTEM
205 Trigger events for devices which belong to a matching subsystem.
206 This option supports shell style pattern matching. When this option
207 is specified more than once, then each matching result is ORed,
208 that is, all the devices in each subsystem are triggered.
209 -S, --subsystem-nomatch=SUBSYSTEM
211 Do not trigger events for devices which belong to a matching
212 subsystem. This option supports shell style pattern matching. When
213 this option is specified more than once, then each matching result
214 is ANDed, that is, devices which do not match all specified
215 subsystems are triggered.
216 -a, --attr-match=ATTRIBUTE=VALUE
218 Trigger events for devices with a matching sysfs attribute. If a
219 value is specified along with the attribute name, the content of
220 the attribute is matched against the given value using shell style
221 pattern matching. If no value is specified, the existence of the
222 sysfs attribute is checked. When this option is specified multiple
223 times, then each matching result is ANDed, that is, only devices
224 which have all specified attributes are triggered.
225 -A, --attr-nomatch=ATTRIBUTE=VALUE
227 Do not trigger events for devices with a matching sysfs attribute.
228 If a value is specified along with the attribute name, the content
229 of the attribute is matched against the given value using shell
230 style pattern matching. If no value is specified, the existence of
231 the sysfs attribute is checked. When this option is specified
232 multiple times, then each matching result is ANDed, that is, only
233 devices which have none of the specified attributes are triggered.
234 -p, --property-match=PROPERTY=VALUE
236 Trigger events for devices with a matching property value. This
237 option supports shell style pattern matching. When this option is
238 specified more than once, then each matching result is ORed, that
239 is, devices which have one of the specified properties are
240 triggered.
241 -g, --tag-match=TAG
243 Trigger events for devices with a matching tag. When this option is
244 specified multiple times, then each matching result is ANDed, that
245 is, devices which have all specified tags are triggered.
246 -y, --sysname-match=NAME
248 Trigger events for devices for which the last component (i.e. the
249 filename) of the /sys/ path matches the specified PATH. This option
250 supports shell style pattern matching. When this option is
251 specified more than once, then each matching result is ORed, that
252 is, all devices which have any of the specified NAME are triggered.
253 --name-match=NAME
255 Trigger events for devices with a matching device path. When this
256 option is specified more than once, then each matching result is
257 ORed, that is, all specified devices are triggered.
258 -b, --parent-match=SYSPATH
260 Trigger events for all children of a given device. When this option
261 is specified more than once, then each matching result is ORed,
262 that is, all children of each specified device are triggered.
263 --initialized-match, --initialized-nomatch
265 When --initialized-match is specified, trigger events for devices
266 that are already initialized by systemd-udevd, and skip devices
267 that are not initialized yet.
268 When --initialized-nomatch is specified, trigger events for devices
270 that are not initialized by systemd-udevd yet, and skip devices
271 that are already initialized.
272 Typically, it is essential that applications which intend to use
274 such a match, make sure a suitable udev rule is installed that sets
275 at least one property on devices that shall be matched. See also
276 Initialized Devices section below for more details.
277 WARNING: --initialized-nomatch can potentially save a significant
279 amount of time compared to re-triggering all devices in the system
280 and e.g. can be used to optimize boot time. However, this is not
281 safe to be used in a boot sequence in general. Especially, when
282 udev rules for a device depend on its parent devices (e.g. "ATTRS"
283 or "IMPORT{parent}" keys, see udev(7) for more details), the final
284 state of the device becomes easily unstable with this option.
285 -w, --settle
287 Apart from triggering events, also waits for those events to
288 finish. Note that this is different from calling udevadm settle.
289 udevadm settle waits for all events to finish. This option only
290 waits for events triggered by the same command to finish.
291 --uuid
293 Trigger the synthetic device events, and associate a randomized
294 UUID with each. These UUIDs are printed to standard output, one
295 line for each event. These UUIDs are included in the uevent
296 environment block (in the "SYNTH_UUID=" property) and may be used
297 to track delivery of the generated events.
298 --wait-daemon[=SECONDS]
300 Before triggering uevents, wait for systemd-udevd daemon to be
301 initialized. Optionally takes timeout value. Default timeout is 5
302 seconds. This is equivalent to invoke invoking udevadm control
303 --ping before udevadm trigger.
304 -h, --help
306 Print a short help text and exit.
307 In addition, optional positional arguments can be used to specify
309 device names or sys paths. They must start with /dev/ or /sys/
310 respectively.
311 udevadm settle [options]
313 Watches the udev event queue, and exits if all current events are
314 handled.
315 -t, --timeout=SECONDS
317 Maximum number of seconds to wait for the event queue to become
318 empty. The default value is 120 seconds. A value of 0 will check if
319 the queue is empty and always return immediately. A non-zero value
320 will return an exit code of 0 if queue became empty before timeout
321 was reached, non-zero otherwise.
322 -E, --exit-if-exists=FILE
324 Stop waiting if file exists.
325 -h, --help
327 Print a short help text and exit.
328 See systemd-udev-settle.service(8) for more information.
330 udevadm control option
332 Modify the internal state of the running udev daemon.
333 -e, --exit
335 Signal and wait for systemd-udevd to exit. No option except for
336 --timeout can be specified after this option. Note that
337 systemd-udevd.service contains Restart=always and so as a result,
338 this option restarts systemd-udevd. If you want to stop
339 systemd-udevd.service, please use the following:
340 systemctl stop systemd-udevd-control.socket systemd-udevd-kernel.socket systemd-udevd.service
342 -l, --log-level=value
345 Set the internal log level of systemd-udevd. Valid values are the
346 numerical syslog priorities or their textual representations:
347 emerg, alert, crit, err, warning, notice, info, and debug.
348 -s, --stop-exec-queue
350 Signal systemd-udevd to stop executing new events. Incoming events
351 will be queued.
352 -S, --start-exec-queue
354 Signal systemd-udevd to enable the execution of events.
355 -R, --reload
357 Signal systemd-udevd to reload the rules files and other databases
358 like the kernel module index. Reloading rules and databases does
359 not apply any changes to already existing devices; the new
360 configuration will only be applied to new events.
361 -p, --property=KEY=value
363 Set a global property for all events.
364 -m, --children-max=value
366 Set the maximum number of events, systemd-udevd will handle at the
367 same time.
368 --ping
370 Send a ping message to systemd-udevd and wait for the reply. This
371 may be useful to check that systemd-udevd daemon is running.
372 -t, --timeout=seconds
374 The maximum number of seconds to wait for a reply from
375 systemd-udevd.
376 -h, --help
378 Print a short help text and exit.
379 udevadm monitor [options]
381 Listens to the kernel uevents and events sent out by a udev rule and
382 prints the devpath of the event to the console. It can be used to
383 analyze the event timing, by comparing the timestamps of the kernel
384 uevent and the udev event.
385 -k, --kernel
387 Print the kernel uevents.
388 -u, --udev
390 Print the udev event after the rule processing.
391 -p, --property
393 Also print the properties of the event.
394 -s, --subsystem-match=string[/string]
396 Filter kernel uevents and udev events by subsystem[/devtype]. Only
397 events with a matching subsystem value will pass. When this option
398 is specified more than once, then each matching result is ORed,
399 that is, all devices in the specified subsystems are monitored.
400 -t, --tag-match=string
402 Filter udev events by tag. Only udev events with a given tag
403 attached will pass. When this option is specified more than once,
404 then each matching result is ORed, that is, devices which have one
405 of the specified tags are monitored.
406 -h, --help
408 Print a short help text and exit.
409 udevadm test [options] [devpath|file|unit]
411 Simulate a udev event run for the given device, and print debug output.
412 -a, --action=ACTION
414 Type of event to be simulated. Possible actions are "add",
415 "remove", "change", "move", "online", "offline", "bind", and
416 "unbind". Also, the special value "help" can be used to list the
417 possible actions. The default value is "add".
418 -N, --resolve-names=early|late|never
420 Specify when udevadm should resolve names of users and groups. When
421 set to early (the default), names will be resolved when the rules
422 are parsed. When set to late, names will be resolved for every
423 event. When set to never, names will never be resolved and all
424 devices will be owned by root.
425 -h, --help
427 Print a short help text and exit.
428 udevadm test-builtin [options] [command] [devpath|file|unit]
430 Run a built-in command COMMAND for device DEVPATH, and print debug
431 output.
432 -a, --action=ACTION
434 Type of event to be simulated. Possible actions are "add",
435 "remove", "change", "move", "online", "offline", "bind", and
436 "unbind". Also, the special value "help" can be used to list the
437 possible actions. The default value is "add".
438 -h, --help
440 Print a short help text and exit.
441 udevadm wait [options] [device|syspath] ...
443 Wait for devices or device symlinks being created and initialized by
444 systemd-udevd. Each device path must start with "/dev/" or "/sys/",
445 e.g. "/dev/sda", "/dev/disk/by-path/pci-0000:3c:00.0-nvme-1-part1",
446 "/sys/devices/pci0000:00/0000:00:1f.6/net/eth0", or
447 "/sys/class/net/eth0". This can take multiple devices. This may be
448 useful for waiting for devices being processed by systemd-udevd after
449 e.g. partitioning or formatting the devices.
450 -t, --timeout=SECONDS
452 Maximum number of seconds to wait for the specified devices or
453 device symlinks being created, initialized, or removed. The default
454 value is "infinity".
455 --initialized=BOOL
457 Check if systemd-udevd initialized devices. Defaults to true. When
458 false, the command only checks if the specified devices exist. Set
459 false to this setting if there is no udev rules for the specified
460 devices, as the devices will never be considered as initialized in
461 that case. See Initialized Devices section below for more details.
462 --removed
464 When specified, the command wait for devices being removed instead
465 of created or initialized. If this is specified, --initialized=
466 will be ignored.
467 --settle
469 When specified, also watches the udev event queue, and wait for all
470 queued events being processed by systemd-udevd.
471 -h, --help
473 Print a short help text and exit.
474 udevadm lock [options] [command] ...
476 udevadm lock takes an (advisory) exclusive lock(s) on a block device
477 (or multiple thereof), as per Locking Block Device Access[1] and
478 invokes a program with the lock(s) taken. When the invoked program
479 exits the lock(s) are automatically released and its return value is
480 propagated as exit code of udevadm lock.
481 This tool is in particular useful to ensure that systemd-
483 udevd.service(8) does not probe a block device while changes are made
484 to it, for example partitions created or file systems formatted. Note
485 that many tools that interface with block devices natively support
486 taking relevant locks, see for example sfdisk(8)'s --lock switch.
487 The command expects at least one block device specified via --device=
489 or --backing=, and a command line to execute as arguments.
490 --device=DEVICE, -d DEVICE
492 Takes a path to a device node of the device to lock. This switch
493 may be used multiple times (and in combination with --backing=) in
494 order to lock multiple devices. If a partition block device node is
495 specified the containing "whole" block device is automatically
496 determined and used for the lock, as per the specification. If
497 multiple devices are specified, they are deduplicated, sorted by
498 the major/minor of their device nodes and then locked in order.
499 This switch must be used at least once, to specify at least one
501 device to lock. (Alternatively, use --backing=, see below.)
502 --backing=PATH, -b PATH
504 If a path to a device node is specified, identical to --device=.
505 However, this switch alternatively accepts a path to a regular file
506 or directory, in which case the block device of the file system the
507 file/directory resides on is automatically determined and used as
508 if it was specified with --device=.
509 --timeout=SECS, -t SECS
511 Specifies how long to wait at most until all locks can be taken.
512 Takes a value in seconds, or in the usual supported time units, see
513 systemd.time(7). If specified as zero the lock is attempted and if
514 not successful the invocation will immediately fail. If passed as
515 "infinity" (the default) the invocation will wait indefinitely
516 until the lock can be acquired. If the lock cannot be taken in the
517 specified time the specified command will not be executed and the
518 invocation will fail.
519 --print, -p
521 Instead of locking the specified device(s) and executing a command,
522 just print the device path(s) that would be locked, and execute no
523 command. This command is useful to determine the "whole" block
524 device in case a partition block device is specified. The devices
525 will be sorted by their device node major number as primary
526 ordering key and the minor number as secondary ordering key (i.e.
527 they are shown in the order they'd be locked). Note that the number
528 of lines printed here can be less than the the number of --device=
529 and --backing= switches specified in case these resolve to the same
530 "whole" devices.
531 -h, --help
533 Print a short help text and exit.
534
536 Initialized devices are those for which at least one udev rule already
537 completed execution – for any action but "remove" — that set a property
538 or other device setting (and thus has an entry in the udev device
539 database). Devices are no longer considered initialized if a "remove"
540 action is seen for them (which removes their entry in the udev device
541 database). Note that devices that have no udev rules are never
542 considered initialized, but might still be announced via the sd-device
543 API (or similar).
544
546 Example 1. Format a File System
547 Take a lock on the backing block device while creating a file system,
549 to ensure that systemd-udevd doesn't probe or announce the new
550 superblock before it is comprehensively written:
551 # udevadm lock --device=/dev/sda1 mkfs.ext4 /dev/sda1
553 Example 2. Format a RAID File System
555 Similar, but take locks on multiple devices at once:
557 # udevadm lock --device=/dev/sda1 --device=/dev/sdb1 mkfs.btrfs /dev/sda1 /dev/sdb1
559 Example 3. Copy in a File System
561 Take a lock on the backing block device while copying in a prepared
563 file system image, to ensure that systemd-udevd doesn't probe or
564 announce the new superblock before it is fully written:
565 # udevadm lock -d /dev/sda1 dd if=fs.raw of=/dev/sda1
567
569 udev(7), systemd-udevd.service(8)
570
572 1. Locking Block Device Access
573 https://systemd.io/BLOCK_DEVICE_LOCKING
574systemd 251 UDEVADM(8)