UDEVD(8)

NAME
udevd, udevdsend - udev event serializer daemon and udev event sender

SYNOPSIS
udevsend hotplug-subsystem

DESCRIPTION
udevd allows the serialization of hotplug(8) events. The events generated by the kernel may arrive in random order in userspace, that makes it neccessary to reorder them.
udevd takes care of the kernel supplied SEQNUM sequence number and arranges the events for execution in the correct order. Missing sequences delay the execution of the following events until a timeout is reached. Events without any sequence number are bypassing the queue and will be executed immediately.
For each event a udev(8) instance is executed in the background with the complete environment received by the hotplug event. All further events for the same device are delayed until the execution is finished. This way there will never be more than one instance running for a single device at the same time.
udevd receives the events from udevsend If udevd isn't already running, udevsend will start it.

ENVIRONMENT

The following variables are read from the environment:

UDEVD_EXPECTED_SEQNUM
    Sets the initial hotplug sequence number. If udevd is not started from initramfs, this should be set to the current hotplug event sequence number as given by /sys/kernel/hotplug_seqnum

UDEVD_EVENT_TIMEOUT
    Second udev should wait before trying to execute the hotplug event. Default is 2.

UDEVD_PIDFILE
    The pathname of the pid file. If empty or not specified, udevd will not write a pid file.

UDEVD_MAX_CHILDS
    Maximum number of concurrently running udev processes. Default is '0', ie no limit.

SIGNALS

udevd reacts to the following signals:

SIGUSR1
    Stops processing of events. Hotplug events are received but not executed. Instead they will be queued for later processing.

SIGUSR2
    Resumes event processing. All events currently stored will be executed.

SEE ALSO
udev(8), udevsend(8), udevinfo(8), hotplug(8)

AUTHORS
udevd was developed primarily by Kay Sievers <kay.sievers@vrfy.org>, with much help from others.