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 --no-pager
123 Do not pipe output into a pager.
124 The generated output shows the current device database entry in a terse
126 format. Each line shown is prefixed with one of the following
127 characters:
128 Table 1. udevadm info output prefixes
130 ┌───────┬────────────────────────────┐
131 │Prefix │ Meaning │
132 ├───────┼────────────────────────────┤
133 │"P:" │ Device path in /sys/ │
134 ├───────┼────────────────────────────┤
135 │"M:" │ Device name in /sys/ (i.e. │
136 │ │ the last component of │
137 │ │ "P:") │
138 ├───────┼────────────────────────────┤
139 │"R:" │ Device number in /sys/ │
140 │ │ (i.e. the numeric suffix │
141 │ │ of the last component of │
142 │ │ "P:") │
143 ├───────┼────────────────────────────┤
144 │"U:" │ Kernel subsystem │
145 ├───────┼────────────────────────────┤
146 │"T:" │ Kernel device type within │
147 │ │ subsystem │
148 ├───────┼────────────────────────────┤
149 │"D:" │ Kernel device node │
150 │ │ major/minor │
151 ├───────┼────────────────────────────┤
152 │"I:" │ Network interface index │
153 ├───────┼────────────────────────────┤
154 │"N:" │ Kernel device node name │
155 ├───────┼────────────────────────────┤
156 │"L:" │ Device node symlink │
157 │ │ priority │
158 ├───────┼────────────────────────────┤
159 │"S:" │ Device node symlink │
160 ├───────┼────────────────────────────┤
161 │"Q:" │ Block device sequence │
162 │ │ number (DISKSEQ) │
163 ├───────┼────────────────────────────┤
164 │"V:" │ Attached driver │
165 ├───────┼────────────────────────────┤
166 │"E:" │ Device property │
167 └───────┴────────────────────────────┘
168 udevadm trigger [options] [devpath|file|unit]
170 Request device events from the kernel. Primarily used to replay events
171 at system coldplug time.
172 Takes device specifications as positional arguments. See the
174 description of info above.
175 -v, --verbose
177 Print the list of devices which will be triggered.
178 -n, --dry-run
180 Do not actually trigger the event.
181 -q, --quiet
183 Suppress error logging in triggering events.
184 -t, --type=TYPE
186 Trigger a specific type of devices. Valid types are "all",
187 "devices", and "subsystems". The default value is "devices".
188 -c, --action=ACTION
190 Type of event to be triggered. Possible actions are "add",
191 "remove", "change", "move", "online", "offline", "bind", and
192 "unbind". Also, the special value "help" can be used to list the
193 possible actions. The default value is "change".
194 --prioritized-subsystem=SUBSYSTEM[,SUBSYSTEM...]
196 Takes a comma separated list of subsystems. When triggering events
197 for devices, the devices from the specified subsystems and their
198 parents are triggered first. For example, if
199 --prioritized-subsystem=block,net, then firstly all block devices
200 and their parents are triggered, in the next all network devices
201 and their parents are triggered, and lastly the other devices are
202 triggered. This option can be specified multiple times, and in that
203 case the lists of the subsystems will be merged. That is,
204 --prioritized-subsystem=block --prioritized-subsystem=net is
205 equivalent to --prioritized-subsystem=block,net.
206 -s, --subsystem-match=SUBSYSTEM
208 Trigger events for devices which belong to a matching subsystem.
209 This option supports shell style pattern matching. When this option
210 is specified more than once, then each matching result is ORed,
211 that is, all the devices in each subsystem are triggered.
212 -S, --subsystem-nomatch=SUBSYSTEM
214 Do not trigger events for devices which belong to a matching
215 subsystem. This option supports shell style pattern matching. When
216 this option is specified more than once, then each matching result
217 is ANDed, that is, devices which do not match all specified
218 subsystems are triggered.
219 -a, --attr-match=ATTRIBUTE=VALUE
221 Trigger events for devices with a matching sysfs attribute. If a
222 value is specified along with the attribute name, the content of
223 the attribute is matched against the given value using shell style
224 pattern matching. If no value is specified, the existence of the
225 sysfs attribute is checked. When this option is specified multiple
226 times, then each matching result is ANDed, that is, only devices
227 which have all specified attributes are triggered.
228 -A, --attr-nomatch=ATTRIBUTE=VALUE
230 Do not trigger events for devices with a matching sysfs attribute.
231 If a value is specified along with the attribute name, the content
232 of the attribute is matched against the given value using shell
233 style pattern matching. If no value is specified, the existence of
234 the sysfs attribute is checked. When this option is specified
235 multiple times, then each matching result is ANDed, that is, only
236 devices which have none of the specified attributes are triggered.
237 -p, --property-match=PROPERTY=VALUE
239 Trigger events for devices with a matching property value. This
240 option supports shell style pattern matching. When this option is
241 specified more than once, then each matching result is ORed, that
242 is, devices which have one of the specified properties are
243 triggered.
244 -g, --tag-match=TAG
246 Trigger events for devices with a matching tag. When this option is
247 specified multiple times, then each matching result is ANDed, that
248 is, devices which have all specified tags are triggered.
249 -y, --sysname-match=NAME
251 Trigger events for devices for which the last component (i.e. the
252 filename) of the /sys/ path matches the specified PATH. This option
253 supports shell style pattern matching. When this option is
254 specified more than once, then each matching result is ORed, that
255 is, all devices which have any of the specified NAME are triggered.
256 --name-match=NAME
258 Trigger events for devices with a matching device path. When this
259 option is specified more than once, then each matching result is
260 ORed, that is, all specified devices are triggered.
261 -b, --parent-match=SYSPATH
263 Trigger events for all children of a given device. When this option
264 is specified more than once, then each matching result is ORed,
265 that is, all children of each specified device are triggered.
266 --initialized-match, --initialized-nomatch
268 When --initialized-match is specified, trigger events for devices
269 that are already initialized by systemd-udevd, and skip devices
270 that are not initialized yet.
271 When --initialized-nomatch is specified, trigger events for devices
273 that are not initialized by systemd-udevd yet, and skip devices
274 that are already initialized.
275 Typically, it is essential that applications which intend to use
277 such a match, make sure a suitable udev rule is installed that sets
278 at least one property on devices that shall be matched. See also
279 Initialized Devices section below for more details.
280 WARNING: --initialized-nomatch can potentially save a significant
282 amount of time compared to re-triggering all devices in the system
283 and e.g. can be used to optimize boot time. However, this is not
284 safe to be used in a boot sequence in general. Especially, when
285 udev rules for a device depend on its parent devices (e.g. "ATTRS"
286 or "IMPORT{parent}" keys, see udev(7) for more details), the final
287 state of the device becomes easily unstable with this option.
288 -w, --settle
290 Apart from triggering events, also waits for those events to
291 finish. Note that this is different from calling udevadm settle.
292 udevadm settle waits for all events to finish. This option only
293 waits for events triggered by the same command to finish.
294 --uuid
296 Trigger the synthetic device events, and associate a randomized
297 UUID with each. These UUIDs are printed to standard output, one
298 line for each event. These UUIDs are included in the uevent
299 environment block (in the "SYNTH_UUID=" property) and may be used
300 to track delivery of the generated events.
301 --wait-daemon[=SECONDS]
303 Before triggering uevents, wait for systemd-udevd daemon to be
304 initialized. Optionally takes timeout value. Default timeout is 5
305 seconds. This is equivalent to invoke invoking udevadm control
306 --ping before udevadm trigger.
307 -h, --help
309 Print a short help text and exit.
310 In addition, optional positional arguments can be used to specify
312 device names or sys paths. They must start with /dev/ or /sys/
313 respectively.
314 udevadm settle [options]
316 Watches the udev event queue, and exits if all current events are
317 handled.
318 -t, --timeout=SECONDS
320 Maximum number of seconds to wait for the event queue to become
321 empty. The default value is 120 seconds. A value of 0 will check if
322 the queue is empty and always return immediately. A non-zero value
323 will return an exit code of 0 if queue became empty before timeout
324 was reached, non-zero otherwise.
325 -E, --exit-if-exists=FILE
327 Stop waiting if file exists.
328 -h, --help
330 Print a short help text and exit.
331 See systemd-udev-settle.service(8) for more information.
333 udevadm control option
335 Modify the internal state of the running udev daemon.
336 -e, --exit
338 Signal and wait for systemd-udevd to exit. No option except for
339 --timeout can be specified after this option. Note that
340 systemd-udevd.service contains Restart=always and so as a result,
341 this option restarts systemd-udevd. If you want to stop
342 systemd-udevd.service, please use the following:
343 systemctl stop systemd-udevd-control.socket systemd-udevd-kernel.socket systemd-udevd.service
345 -l, --log-level=value
348 Set the internal log level of systemd-udevd. Valid values are the
349 numerical syslog priorities or their textual representations:
350 emerg, alert, crit, err, warning, notice, info, and debug.
351 -s, --stop-exec-queue
353 Signal systemd-udevd to stop executing new events. Incoming events
354 will be queued.
355 -S, --start-exec-queue
357 Signal systemd-udevd to enable the execution of events.
358 -R, --reload
360 Signal systemd-udevd to reload the rules files and other databases
361 like the kernel module index. Reloading rules and databases does
362 not apply any changes to already existing devices; the new
363 configuration will only be applied to new events.
364 -p, --property=KEY=value
366 Set a global property for all events.
367 -m, --children-max=value
369 Set the maximum number of events, systemd-udevd will handle at the
370 same time.
371 --ping
373 Send a ping message to systemd-udevd and wait for the reply. This
374 may be useful to check that systemd-udevd daemon is running.
375 -t, --timeout=seconds
377 The maximum number of seconds to wait for a reply from
378 systemd-udevd.
379 -h, --help
381 Print a short help text and exit.
382 udevadm monitor [options]
384 Listens to the kernel uevents and events sent out by a udev rule and
385 prints the devpath of the event to the console. It can be used to
386 analyze the event timing, by comparing the timestamps of the kernel
387 uevent and the udev event.
388 -k, --kernel
390 Print the kernel uevents.
391 -u, --udev
393 Print the udev event after the rule processing.
394 -p, --property
396 Also print the properties of the event.
397 -s, --subsystem-match=string[/string]
399 Filter kernel uevents and udev events by subsystem[/devtype]. Only
400 events with a matching subsystem value will pass. When this option
401 is specified more than once, then each matching result is ORed,
402 that is, all devices in the specified subsystems are monitored.
403 -t, --tag-match=string
405 Filter udev events by tag. Only udev events with a given tag
406 attached will pass. When this option is specified more than once,
407 then each matching result is ORed, that is, devices which have one
408 of the specified tags are monitored.
409 -h, --help
411 Print a short help text and exit.
412 udevadm test [options] [devpath|file|unit]
414 Simulate a udev event run for the given device, and print debug output.
415 -a, --action=ACTION
417 Type of event to be simulated. Possible actions are "add",
418 "remove", "change", "move", "online", "offline", "bind", and
419 "unbind". Also, the special value "help" can be used to list the
420 possible actions. The default value is "add".
421 -N, --resolve-names=early|late|never
423 Specify when udevadm should resolve names of users and groups. When
424 set to early (the default), names will be resolved when the rules
425 are parsed. When set to late, names will be resolved for every
426 event. When set to never, names will never be resolved and all
427 devices will be owned by root.
428 -h, --help
430 Print a short help text and exit.
431 udevadm test-builtin [options] [command] [devpath|file|unit]
433 Run a built-in command COMMAND for device DEVPATH, and print debug
434 output.
435 -a, --action=ACTION
437 Type of event to be simulated. Possible actions are "add",
438 "remove", "change", "move", "online", "offline", "bind", and
439 "unbind". Also, the special value "help" can be used to list the
440 possible actions. The default value is "add".
441 -h, --help
443 Print a short help text and exit.
444 udevadm wait [options] [device|syspath] ...
446 Wait for devices or device symlinks being created and initialized by
447 systemd-udevd. Each device path must start with "/dev/" or "/sys/",
448 e.g. "/dev/sda", "/dev/disk/by-path/pci-0000:3c:00.0-nvme-1-part1",
449 "/sys/devices/pci0000:00/0000:00:1f.6/net/eth0", or
450 "/sys/class/net/eth0". This can take multiple devices. This may be
451 useful for waiting for devices being processed by systemd-udevd after
452 e.g. partitioning or formatting the devices.
453 -t, --timeout=SECONDS
455 Maximum number of seconds to wait for the specified devices or
456 device symlinks being created, initialized, or removed. The default
457 value is "infinity".
458 --initialized=BOOL
460 Check if systemd-udevd initialized devices. Defaults to true. When
461 false, the command only checks if the specified devices exist. Set
462 false to this setting if there is no udev rules for the specified
463 devices, as the devices will never be considered as initialized in
464 that case. See Initialized Devices section below for more details.
465 --removed
467 When specified, the command wait for devices being removed instead
468 of created or initialized. If this is specified, --initialized=
469 will be ignored.
470 --settle
472 When specified, also watches the udev event queue, and wait for all
473 queued events being processed by systemd-udevd.
474 -h, --help
476 Print a short help text and exit.
477 udevadm lock [options] [command] ...
479 udevadm lock takes an (advisory) exclusive lock on a block device (or
480 all specified devices), as per Locking Block Device Access[1] and
481 invokes a program with the locks taken. When the invoked program exits
482 the locks are automatically released and its return value is propagated
483 as exit code of udevadm lock.
484 This tool is in particular useful to ensure that systemd-
486 udevd.service(8) does not probe a block device while changes are made
487 to it, for example partitions created or file systems formatted. Note
488 that many tools that interface with block devices natively support
489 taking relevant locks, see for example sfdisk(8)'s --lock switch.
490 The command expects at least one block device specified via --device=
492 or --backing=, and a command line to execute as arguments.
493 --device=DEVICE, -d DEVICE
495 Takes a path to a device node of the device to lock. This switch
496 may be used multiple times (and in combination with --backing=) in
497 order to lock multiple devices. If a partition block device node is
498 specified the containing "whole" block device is automatically
499 determined and used for the lock, as per the specification. If
500 multiple devices are specified, they are deduplicated, sorted by
501 the major/minor of their device nodes and then locked in order.
502 This switch must be used at least once, to specify at least one
504 device to lock. (Alternatively, use --backing=, see below.)
505 --backing=PATH, -b PATH
507 If a path to a device node is specified, identical to --device=.
508 However, this switch alternatively accepts a path to a regular file
509 or directory, in which case the block device of the file system the
510 file/directory resides on is automatically determined and used as
511 if it was specified with --device=.
512 --timeout=SECS, -t SECS
514 Specifies how long to wait at most until all locks can be taken.
515 Takes a value in seconds, or in the usual supported time units, see
516 systemd.time(7). If specified as zero the lock is attempted and if
517 not successful the invocation will immediately fail. If passed as
518 "infinity" (the default) the invocation will wait indefinitely
519 until the lock can be acquired. If the lock cannot be taken in the
520 specified time the specified command will not be executed and the
521 invocation will fail.
522 --print, -p
524 Instead of locking the specified devices and executing a command,
525 just print the device paths that would be locked, and execute no
526 command. This command is useful to determine the "whole" block
527 device in case a partition block device is specified. The devices
528 will be sorted by their device node major number as primary
529 ordering key and the minor number as secondary ordering key (i.e.
530 they are shown in the order they'd be locked). Note that the number
531 of lines printed here can be less than the number of --device= and
532 --backing= switches specified in case these resolve to the same
533 "whole" devices.
534 -h, --help
536 Print a short help text and exit.
537
539 Initialized devices are those for which at least one udev rule already
540 completed execution – for any action but "remove" — that set a property
541 or other device setting (and thus has an entry in the udev device
542 database). Devices are no longer considered initialized if a "remove"
543 action is seen for them (which removes their entry in the udev device
544 database). Note that devices that have no udev rules are never
545 considered initialized, but might still be announced via the sd-device
546 API (or similar).
547
549 Example 1. Format a File System
550 Take a lock on the backing block device while creating a file system,
552 to ensure that systemd-udevd doesn't probe or announce the new
553 superblock before it is comprehensively written:
554 # udevadm lock --device=/dev/sda1 mkfs.ext4 /dev/sda1
556 Example 2. Format a RAID File System
558 Similar, but take locks on multiple devices at once:
560 # udevadm lock --device=/dev/sda1 --device=/dev/sdb1 mkfs.btrfs /dev/sda1 /dev/sdb1
562 Example 3. Copy in a File System
564 Take a lock on the backing block device while copying in a prepared
566 file system image, to ensure that systemd-udevd doesn't probe or
567 announce the new superblock before it is fully written:
568 # udevadm lock -d /dev/sda1 dd if=fs.raw of=/dev/sda1
570
572 udev(7), systemd-udevd.service(8)
573
575 1. Locking Block Device Access
576 https://systemd.io/BLOCK_DEVICE_LOCKING
577systemd 253 UDEVADM(8)