systemd-udevd.service(8) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | OPTIONS | KERNEL COMMAND LINE | SEE ALSO | COLOPHON

SYSTEMD-UDEVD.SERVICE(8)  systemd-udevd.service SYSTEMD-UDEVD.SERVICE(8)

NAME         top

       systemd-udevd.service, systemd-udevd-control.socket, systemd-
       udevd-kernel.socket, systemd-udevd - Device event managing daemon

SYNOPSIS         top

       systemd-udevd.service

       systemd-udevd-control.socket

       systemd-udevd-kernel.socket

       /usr/lib/systemd/systemd-udevd [--daemon] [--debug]
                                      [--children-max=] [--exec-delay=]
                                      [--event-timeout=]
                                      [--resolve-names=early|late|never]
                                      [--version] [--help]

DESCRIPTION         top

       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.

OPTIONS         top

       -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.

KERNEL COMMAND LINE         top

       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.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.

SEE ALSO         top

       udev.conf(5), udev(7), udevadm(8)

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 2023-12-22.  (At that
       time, the date of the most recent commit that was found in the
       repository was 2023-12-22.)  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 255                                     SYSTEMD-UDEVD.SERVICE(8)

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