lfs-book/chapter06/devices.xml

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<sect1 id="ch-system-devices">
  <?dbhtml filename="devices.html"?>

  <title>Populating /dev</title>

  <indexterm zone="ch-system-devices">
    <primary sortas="e-/dev/">/dev/*</primary>
  </indexterm>

  <sect2>
    <title>Creating Initial Device Nodes</title>

    <para>When the kernel boots the system, it requires the presence of a few
    device nodes, in particular the <filename class="devicefile">console</filename>
    and <filename class="devicefile">null</filename> devices. The device nodes
    will be created on the hard disk so that they are available before
    <command>udev</command> has been started, and additionally when Linux is
    started in single user mode (hence the restrictive permissions on
    <filename class="devicefile">console</filename>). Create the devices by
    running the following commands:</para>

<screen><userinput>mknod -m 600 /dev/console c 5 1
mknod -m 666 /dev/null c 1 3</userinput></screen>

  </sect2>

  <sect2>
    <title>Mounting tmpfs and Populating /dev</title>

    <para>The recommended method of populating the <filename
    class="directory">/dev</filename> directory with devices is to mount a
    virtual filesystem (such as <systemitem class="filesystem">tmpfs</systemitem>)
    on the <filename class="directory">/dev</filename> directory, and allow the
    devices to be created dynamically on that virtual filesystem as they are
    detected or accessed. This is generally done during the boot process. Since
    this new system has not been booted, it is necessary to do what the
    LFS-Bootscripts package would otherwise do by mounting <filename
    class="directory">/dev</filename>:</para>

<screen><userinput>mount -nvt tmpfs none /dev</userinput></screen>

    <para>The Udev package is what actually creates the devices in the <filename
    class="directory">/dev</filename> directory. Since it will not be installed
    until later on in the process, manually create the minimal set of device nodes
    needed to complete the building of this system:</para>

<screen><userinput>mknod -m 622 /dev/console c 5 1
mknod -m 666 /dev/null c 1 3
mknod -m 666 /dev/zero c 1 5
mknod -m 666 /dev/ptmx c 5 2
mknod -m 666 /dev/tty c 5 0
mknod -m 444 /dev/random c 1 8
mknod -m 444 /dev/urandom c 1 9
chown -v root:tty /dev/{console,ptmx,tty}</userinput></screen>

    <para>There are some symlinks and directories required by LFS that are
    created during system startup by the LFS-Bootscripts package. Since this
    is a chroot environment and not a booted environment, those symlinks and
    directories need to be created here:</para>

<screen><userinput>ln -sv /proc/self/fd /dev/fd
ln -sv /proc/self/fd/0 /dev/stdin
ln -sv /proc/self/fd/1 /dev/stdout
ln -sv /proc/self/fd/2 /dev/stderr
ln -sv /proc/kcore /dev/core
mkdir -v /dev/pts
mkdir -v /dev/shm</userinput></screen>

    <para>Finally, mount the proper virtual (kernel) file systems on the
    newly-created directories:</para>

<screen><userinput>mount -vt devpts -o gid=4,mode=620 none /dev/pts
mount -vt tmpfs none /dev/shm</userinput></screen>

    <para>The <command>mount</command> commands executed above may result
    in the following warning message:</para>

<screen><computeroutput>can't open /etc/fstab: No such file or directory.</computeroutput></screen>

    <para>This file&mdash;<filename>/etc/fstab</filename>&mdash;has not
    been created yet but is also not required for the file systems to be
    properly mounted. As such, the warning can be safely ignored.</para>

  </sect2>

</sect1>