Fedora 下的Udev

This document tries to reveal the secrets of udev and how it works on Fedora.

本文解释为什么fedora下挂载光盘要用 mount /dev/hdc /media/cdrecorder

udev provides a dynamic device directory containing only the files for actually present devices. It creates or removes device node files usually located in the /dev directory, or it renames network interfaces.

As part of the hotplug subsystem, udev is executed if a kernel device is added or removed from the system. On device creation, udev reads the sysfs directory of the given device to collect device attributes like label, serial number or bus device number. These attributes may be used as keys to determine a unique name for the device. udev maintains a database for devices present on the system. On device removal, udev queries its database for the name of the device file to be deleted.

udev gets called by hotplug, if a module is loaded, and a device is added or removed. udev looks in /sys, if the driver provides a "dev" file, which contains the major and minor number for a device node to communicate with the driver. After looking in the udev rules (/etc/udev/rules.d), which specify the device node filename and symlinks, a device node is created in /dev with the permissions, which are specified in /etc/udev/permissions.d.

But I really want my device node!

Put them in /etc/udev/devices/ and they will get copied to /dev. File a bugzilla entry, if you think that should be done per default.

可以理解为什么在fedora下 mount光盘要用 /dev/hdc