About Devices

Although most devices needed by packages in BLFS and beyond are set up properly by udev using the default rules installed by LFS in /etc/udev/rules.d, there are cases where the rules must be modified or augmented.

User Notes: http://wiki.linuxfromscratch.org/blfs/wiki/aboutdevices

Multiple Sound Cards

If there are multiple sound cards in a system, the "default" sound card becomes random. The method to establish sound card order depends on whether the drivers are modules or not. If the sound card drivers are compiled into the kernel, control is via kernel command line parameters in /boot/grub/menu.lst. For example, if a system has both an FM801 card and a SoundBlaster PCI card, the following can be appended to the command line:

snd-fm801.index=0 snd-ens1371.index=1

If the sound card drivers are built as modules, the order can be established in the /etc/modprobe.conf file with:

options snd-fm801 index=0
options snd-ens1371 index=1

Udev Device Attrubutes

Fine-tuning of device attributes such as group name and permissions is possible by creating extra udev rules, matching on something like this (on one line). The vendor and product can be found by searching the /sys/devices directory entries or using udevinfo after the device has been attached. See the documentation in the current udev directory of /usr/share/doc for details.

SUBSYSTEM=="usb_device", SYSFS{idVendor}=="05d8",
   SYSFS{idProduct}=="4002", GROUP:="scanner", MODE:="0640"

USB Device Issues

Some older applications, such as VMware, need the following deprecated entry in the /etc/fstab file. This is not normally needed.

usbfs  /proc/bus/usb  usbfs  devgid=14,devmode=0660  0  0

Devices for Servers

In some cases, it makes sense to disable udev completely and create static devices. Servers are one example of this situation. Does a server need the capability of handling dynamic devices? Only the system administrator can answer that question, but in many cases the answer will be no.

If dynamic devices are not desired, then static devices must be created on the system. In the default configuration, the /etc/rc.d/rcsysinit.d/S10udev boot script mounts a tmpfs partition over the /dev directory. This problem can be overcome by mounting the root partition temporarily:



If the instructions below are not followed carefully, your system could become unbootable.

mount --bind / /mnt
cp -a /dev/* /mnt/dev
rm /etc/rc.d/rcsysinit.d/{S10udev,S45udev_retry}
umount /mnt

At this point, the system will use static devices upon the next reboot. Create any desired additional devices using mknod.

If you want to restore the dynamic devices, recreate the /etc/rc.d/rcsysinit.d/{S10udev,S45udev_retry} symbolic links and reboot again. Static devices do not need to be removed (console and null are always needed) because they are covered by the tmpfs partition. Disk usage for devices is negligible (about 20–30 bytes per entry.)

Last updated on 2006-09-23 10:46:31 -0500