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7.6.3. Udev Bootscripts
The /etc/rc.d/init.d/udev initscript starts udevd, triggers any "coldplug" devices that have already been created by the kernel and waits for any rules to complete. The script also unsets the uevent handler from the default of
/sbin/hotplug . This is done because the kernel no longer needs to call out to an external binary. Instead udevd
will listen on a netlink socket for uevents that the kernel raises.
The /etc/rc.d/init.d/udev_retry initscript takes care of re-triggering events for subsystems whose rules may rely on filesystems that are not mounted until the mountfs script is run (in particular, /usr and /var may cause this). This script runs after the mountfs script, so those rules (if re-triggered) should succeed the second time around. It is configured from the /etc/sysconfig/udev_retry file; any words in this file other than comments are considered subsystem names to trigger at retry time. To find the subsystem of a device, use udevadm info --attribute- walk <device> where <device> is an absolute path in /dev or /sys such as /dev/sr0 or /sys/class/rtc.
For information on kernel module loading and udev, see Section 7.3.2.3, “Module Loading”.