NAME

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

SYNOPSIS

       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

       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

       -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

       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

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