source: postlfs/config/devices.xml@ aaa763cd

<?xml version="1.0" encoding="ISO-8859-1"?>
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   "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [
  <!ENTITY % general-entities SYSTEM "../../general.ent">
  %general-entities;
]>

<sect1 id="postlfs-devices" xreflabel="About Devices">
  <?dbhtml filename="devices.html"?>

  <sect1info>
    <othername>$LastChangedBy$</othername>
    <date>$Date$</date>
  </sect1info>

  <title>About Devices</title>

  <indexterm zone="postlfs-devices">
    <primary sortas="e-etc-udev-rules">/etc/udev/rules.d</primary>
  </indexterm>


  <para>Although most devices needed by packages in BLFS and beyond are set up
  properly by <application>udev</application> using the default rules installed
  by LFS in <filename class="directory">/etc/udev/rules.d</filename>, there are
  cases where the rules must be modified or augmented.</para>

  <para condition="html" role="usernotes">User Notes:
  <ulink url="&blfs-wiki;/aboutdevices"/></para>

  <sect2>
    <title>Multiple Sound Cards</title>

    <para>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 <filename>/boot/grub/menu.lst</filename>.  For example,
    if a system has both an FM801 card and a SoundBlaster PCI card, the
    following can be appended to the command line:</para>

<screen><literal>snd-fm801.index=0 snd-ens1371.index=1</literal></screen>

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

<screen><literal>options snd-fm801 index=0
options snd-ens1371 index=1</literal></screen>

  </sect2>

  <sect2>
    <title>Udev Device Attributes</title>

    <para>Fine-tuning of device attributes such as group name and permissions
    is possible by creating extra <application>udev</application> rules,
    matching on something like this. The vendor and product can
    be found by searching the /sys/devices directory entries or using
    <command>udevadm info</command> after the device has been attached. See the
    documentation in the current <application>udev</application>  directory of
    <filename class='directory'>/usr/share/doc</filename> for details.</para>

<screen><literal>SUBSYSTEM=="usb_device", SYSFS{idVendor}=="05d8", SYSFS{idProduct}=="4002", \
  GROUP:="scanner", MODE:="0660"</literal></screen>

    <note><para>The above line is used for descriptive purposes only. The
    scanner <application>udev</application> rules are put into place when
    installing <xref linkend='sane'/>.</para></note>

  </sect2>

  <sect2>
    <title>USB Device Issues</title>

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

<screen><literal>usbfs  /proc/bus/usb  usbfs  devgid=14,devmode=0660  0  0</literal></screen>

  </sect2>

<!--
  <sect2>
    <title>Multiple Network Interfaces</title>


  </sect2>
-->

  <sect2>
    <title>Devices for Servers</title>

    <para>In some cases, it makes sense to disable
    <application>udev</application> 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.</para>

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

    <warning><para>If the instructions below are not followed carefully, your
    system could become unbootable.</para></warning>


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

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

    <para>If you want to restore the dynamic devices, recreate the
    <filename>/etc/rc.d/rcsysinit.d/{S10udev,S45udev_retry}</filename> 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 <systemitem
    class="filesystem">tmpfs</systemitem> partition.  Disk usage for devices is
    negligible (about 20&ndash;30 bytes per entry.)</para>

  </sect2>

</sect1>