Linux From Scratch - Version 6.5-rc2

Chapter 6. Installing Basic System Software

6.57. Udev-145

The Udev package contains programs for dynamic creation of device nodes.

Approximate build time: 0.2 SBU
Required disk space: 11.6 MB

6.57.1. Installation of Udev

The udev-config tarball contains LFS-specific files used to configure Udev. Unpack it into the Udev source directory: 

tar -xvf ../udev-config-20090523.tar.bz2

Create some devices and directories that Udev cannot handle due to them being required very early in the boot process, or by Udev itself: 

install -dv /lib/{firmware,udev/devices/{pts,shm}}
mknod -m0666 /lib/udev/devices/null c 1 3
mknod -m0600 /lib/udev/devices/kmsg c 1 11
ln -sv /proc/self/fd /lib/udev/devices/fd
ln -sv /proc/self/fd/0 /lib/udev/devices/stdin
ln -sv /proc/self/fd/1 /lib/udev/devices/stdout
ln -sv /proc/self/fd/2 /lib/udev/devices/stderr
ln -sv /proc/kcore /lib/udev/devices/core

Prepare the package for compilation: 

./configure --prefix=/usr \
    --sysconfdir=/etc --sbindir=/sbin \
    --with-rootlibdir=/lib --libexecdir=/lib/udev \
    --disable-extras

The meaning of the new configure options

--with-rootlibdir=/lib

This controls where the libudev library is installed. The library needs to be in /lib because it's used by Udev at boot time, before /usr might be available, and the default --rootlibdir is /usr/lib.

--libexecdir=/lib/udev

This controls where Udev-internal rules and helper programs are installed.

--disable-extras

This option prevents Udev from installing helper programs and other extras which require more external libraries. These libraries are not part of the base LFS system. See the Udev README file for more information.

Compile the package: 

make

This package does not come with a test suite.

Install the package: 

make install

Udev has to be configured in order to work properly, as its default configuration does not cover all devices. First install two extra rules files from Udev to help support device-mapper and RAID setups: 

install -m644 -v rules/packages/64-*.rules \
    /lib/udev/rules.d/

Now install a file to create symlinks for certain hand-held devices: 

install -m644 -v rules/packages/40-pilot-links.rules \
    /lib/udev/rules.d/

Now install a file to handle ISDN devices: 

install -m644 -v rules/packages/40-isdn.rules \
    /lib/udev/rules.d/

Now install the LFS-specific custom rules files: 

cd udev-config-20090523
make install

Install the documentation that explains the LFS-specific rules files: 

make install-doc

Install the documentation that explains the commonly-used rules files provided by Udev: 

make install-extra-doc

6.57.2. Contents of Udev

Installed programs: ata_id, cdrom_id, collect, create_floppy_devices, edd_id, firmware.sh, fstab_import, path_id, scsi_id, udevadm, udevd, usb_id, write_cd_rules, and write_net_rules
Installed libraries: libudev
Installed directory: /etc/udev

Short Descriptions

ata_id

Provides Udev with a unique string and additional information (uuid, label) for an ATA drive

cdrom_id

Provides Udev with the capabilities of a CD-ROM or DVD-ROM drive

collect

Given an ID for the current uevent and a list of IDs (for all target uevents), registers the current ID and indicates whether all target IDs have been registered

create_floppy_devices

Creates all possible floppy devices based on the CMOS type

edd_id

Provides Udev with the EDD ID for a BIOS disk drive

firmware.sh

Uploads firmware to devices

fstab_import

Finds an entry in /etc/fstab that matches the current device, and provides its information to Udev

path_id

Provides the shortest possible unique hardware path to a device

scsi_id

Provides Udev with a unique SCSI identifier based on the data returned from sending a SCSI INQUIRY command to the specified device

udevadm

Generic udev administration tool: controls the udevd daemon, provides info from the Udev database, monitors uevents, waits for uevents to finish, tests Udev configuration, and triggers uevents for a given device

udevd

A daemon that listens for uevents on the netlink socket, creates devices and runs the configured external programs in response to these uevents

usb_id

Provides Udev with information about USB devices

write_cd_rules

A script which generates Udev rules to provide stable names for optical drives (see also Section 7.10, “Creating Custom Symlinks to Devices”)

write_net_rules

A script which generates rules to provide stable names for network interfaces (see also Section 7.13, “Configuring the network Script”)

libudev

A library interface to udev device information

/etc/udev

Contains Udev configuration files, device permissions, and rules for device naming