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NAME | SYNOPSIS | DESCRIPTION | OPTIONS | KERNEL COMMAND LINE | SEE ALSO | COLOPHON |
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SYSTEMD-UDEVD.SERVICE(8) systemd-udevd.service SYSTEMD-UDEVD.SERVICE(8)
systemd-udevd.service, systemd-udevd-control.socket, systemd-
udevd-kernel.socket, systemd-udevd-varlink.socket, systemd-udevd -
Device event managing daemon
systemd-udevd.service
systemd-udevd-control.socket
systemd-udevd-kernel.socket
systemd-udevd-varlink.socket
/usr/lib/systemd/systemd-udevd [--daemon] [--debug]
[--children-max=] [--exec-delay=]
[--event-timeout=]
[--resolve-names=early|late|never]
[--version] [--help]
systemd-udevd listens to kernel uevents. For every event,
systemd-udevd executes matching instructions specified in udev
rules. See udev(7).
The behavior of the daemon can be configured using udev.conf(5),
its command line options, environment variables, and on the kernel
command line, or changed dynamically with udevadm control.
-d, --daemon
Detach and run in the background.
Added in version 186.
-D, --debug
Print debug messages to standard error.
Added in version 186.
-c, --children-max=
Limit the number of events executed in parallel.
Added in version 186.
-e, --exec-delay=
Delay the execution of each RUN{program} parameter by the
given number of seconds. This option might be useful when
debugging system crashes during coldplug caused by loading
non-working kernel modules.
Added in version 186.
-t, --event-timeout=
Set the number of seconds to wait for events to finish. After
this time, the event will be terminated. The default is 180
seconds.
Added in version 216.
-s, --timeout-signal=
Set the signal which systemd-udevd will send to forked off
processes after reaching event timeout. The setting can be
overridden at boot time with the kernel command line option
udev.timeout_signal=. Setting to SIGABRT may be helpful in
order to debug worker timeouts. Defaults to SIGKILL. Note that
setting the option on the command line overrides the setting
from the configuration file.
Added in version 246.
-N, --resolve-names=
Specify when systemd-udevd 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 186.
-h, --help
Print a short help text and exit.
--version
Print a short version string and exit.
Parameters prefixed with "rd." will be read when systemd-udevd is
used in an initrd, those without will be processed both in the
initrd and on the host.
udev.log_level=, rd.udev.log_level=
Set the log level.
Added in version 247.
udev.trace[=BOOL], rd.udev.trace[=BOOL]
Enable/disable trace logging. When enabled, udev.log_level=
will be ignored, and "debug" level is assumed.
Added in version 258.
udev.children_max=, rd.udev.children_max=
Limit the number of events executed in parallel.
Added in version 186.
udev.exec_delay=, rd.udev.exec_delay=
Delay the execution of each RUN{program} parameter by the
given number of seconds. This option might be useful when
debugging system crashes during coldplug caused by loading
non-working kernel modules.
Added in version 186.
udev.event_timeout=, rd.udev.event_timeout=
Wait for events to finish up to the given number of seconds.
This option might be useful if events are terminated due to
kernel drivers taking too long to initialize.
Added in version 216.
udev.timeout_signal=, rd.udev.timeout_signal=
Specifies a signal that systemd-udevd will send to workers on
timeout. Note that kernel command line option overrides both
the setting in the configuration file and the one on the
program command line.
Added in version 246.
udev.blockdev_read_only, rd.udev.blockdev_read_only
If specified, mark all physical block devices read-only as
they appear. Synthetic block devices (such as loopback block
devices or device mapper devices) are left as they are. This
is useful to guarantee that the contents of physical block
devices remains unmodified during runtime, for example to
implement fully stateless systems, for testing or for recovery
situations where corrupted file systems shall not be corrupted
further through accidental modification.
A block device may be marked writable again by issuing the
blockdev --setrw command, see blockdev(8) for details.
Added in version 246.
net.ifnames=
Network interfaces are renamed to give them predictable names
when possible. It is enabled by default; specifying 0 disables
it.
Added in version 199.
net.naming_scheme=
Network interfaces are renamed to give them predictable names
when possible (unless net.ifnames=0 is specified, see above).
With this kernel command line option it is possible to pick a
specific version of this algorithm and override the default
chosen at compilation time. Expects one of the naming scheme
identifiers listed in systemd.net-naming-scheme(7), or
"latest" to select the latest scheme known (to this particular
version of systemd-udevd.service).
Note that selecting a specific scheme is not sufficient to
fully stabilize interface naming: the naming is generally
derived from driver attributes exposed by the kernel. As the
kernel is updated, previously missing attributes
systemd-udevd.service is checking might appear, which affects
older name derivation algorithms, too.
Added in version 240.
net.ifname_policy=policy1[,policy2,...][,MAC]
Specifies naming policies applied when renaming network
interfaces. Takes a list of policies and an optional MAC
address separated with comma. Each policy value must be one of
the policies understood by the NamePolicy= setting in .link
files, e.g. "onboard" or "path". See systemd.link(5) for more
details. When the MAC address is specified, the policies are
applied to the interface which has the address. When no MAC
address is specified, the policies are applied to all
interfaces. This kernel command line argument can be specified
multiple times.
This argument is not directly read by systemd-udevd, but is
instead converted to a .link file by
systemd-network-generator.service(8). For this argument to
take effect, systemd-network-generator.service must be
enabled.
Example:
net.ifname_policy=keep,kernel,path,slot,onboard,01:23:45:67:89:ab
net.ifname_policy=keep,kernel,path,slot,onboard,mac
This is mostly equivalent to creating the following .link
files:
# 91-name-policy-with-mac.link
[Match]
MACAddress=01:23:45:67:89:ab
[Link]
NamePolicy=keep kernel path slot onboard
AlternativeNamePolicy=path slot onboard
and
# 92-name-policy-for-all.link
[Match]
OriginalName=*
[Link]
NamePolicy=keep kernel path slot onboard mac
AlternativeNamePolicy=path slot onboard mac
Added in version 250.
udev.conf(5), udev(7), udevadm(8)
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 2025-08-11. (At that
time, the date of the most recent commit that was found in the
repository was 2025-08-11.) 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 258~rc2 SYSTEMD-UDEVD.SERVICE(8)
Pages that refer to this page: networkctl(1), sd-device(3), sd_device_enumerator_new(3), sd-hwdb(3), sd_hwdb_get(3), sd_hwdb_new(3), udev_new(3), iocost.conf(5), systemd.exec(5), systemd.link(5), udev.conf(5), file-hierarchy(7), kernel-command-line(7), systemd.directives(7), systemd.index(7), systemd.net-naming-scheme(7), systemd.special(7), udev(7), cfdisk(8), fdisk(8), mkfs.bfs(8), mkfs.cramfs(8), mkfs.minix(8), mkswap(8), sfdisk(8), systemd-networkd.service(8), systemd-network-generator.service(8), systemd-vconsole-setup.service(8), udevadm(8), wipefs(8)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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