lfs/chapter07/kernfs.xml

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  "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [
  <!ENTITY % general-entities SYSTEM "../general.ent">
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<sect1 id="ch-tools-kernfs">
  <?dbhtml filename="kernfs.html"?>

  <title>Preparing Virtual Kernel File Systems</title>

  <indexterm zone="ch-tools-kernfs">
    <primary sortas="e-/dev/">/dev/*</primary>
  </indexterm>

    <para>Applications running in user space utilize various file 
    systems exported by the kernel to communicate 
    with the kernel itself. These file systems are virtual: no disk
    space is used for them. The content of the file systems resides in
    memory. These file systems must exist in the $LFS directory tree
    before you can <command>chroot</command> successfully.</para>

    <para>Begin by creating directories on which the file systems will be
    mounted:</para>

<screen><userinput>mkdir -pv $LFS/{dev,proc,sys,run}</userinput></screen>

  <sect2 id="ch-tools-bindmount">
    <title>Mounting and Populating /dev</title>

      <para>During a normal boot, the kernel automatically mounts the
      <systemitem class="filesystem">devtmpfs</systemitem> filesystem on the
      <filename class="directory">/dev</filename> directory; the
      devices are created dynamically on that virtual filesystem when they
      are first detected or accessed. Device creation is generally done during the
      boot process by the kernel and the udev program.
      Since the new system does not yet include udev and
      has not yet been booted, it is necessary to mount and populate
      the <filename class="directory">/dev</filename> directory manually. This is
      accomplished by bind mounting the host system's
      <filename class="directory">/dev</filename> directory. A bind mount is
      a special type of mount that allows you to create a mirror of a
      directory or mount point at some other location. Use the following
      command to do this:</para>

<screen><userinput>mount -v --bind /dev $LFS/dev</userinput></screen>

  </sect2>

  <sect2 id="ch-tools-kernfsmount">
    <title>Mounting Virtual Kernel File Systems</title>

      <para>Now mount the remaining virtual kernel filesystems:</para>

<screen><userinput>mount -v --bind /dev/pts $LFS/dev/pts
mount -vt proc proc $LFS/proc
mount -vt sysfs sysfs $LFS/sys
mount -vt tmpfs tmpfs $LFS/run</userinput></screen>
<!--
    <variablelist>
      <title>The meaning of the mount options for devpts:</title>

      <varlistentry>
        <term><parameter>gid=5</parameter></term>
        <listitem>
          <para>This ensures that all devpts-created device nodes are owned by
          group ID 5.  This is the ID we will use later on for the <systemitem
          class="groupname">tty</systemitem> group.  We use the group ID instead
          of a name, since the host system might use a different ID for its
          <systemitem class="groupname">tty</systemitem> group.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><parameter>mode=0620</parameter></term>
        <listitem>
          <para>This ensures that all devpts-created device nodes have mode 0620
          (user readable and writable, group writable).  Together with the
          option above, this ensures that devpts will create device nodes that
          meet the requirements of grantpt(), meaning the Glibc
          <command>pt_chown</command> helper binary (which is not installed by
          default) is not necessary.</para>
        </listitem>
      </varlistentry>

    </variablelist>
-->
      <para>In some host systems, <filename>/dev/shm</filename> is a
      symbolic link to <filename class="directory">/run/shm</filename>.
      The /run tmpfs was mounted above so in this case only a
      directory needs to be created.</para>

      <para>In other host systems <filename>/dev/shm</filename> is a mount point 
      for a tmpfs. In that case the mount of /dev above will only create
      /dev/shm as a directory in the chroot environment. In this situation
      we must explicitly mount a tmpfs:</para>

<screen><userinput>if [ -h $LFS/dev/shm ]; then
  mkdir -pv $LFS/$(readlink $LFS/dev/shm)
else
  mount -t tmpfs -o nosuid,nodev tmpfs $LFS/dev/shm
fi</userinput></screen>

  </sect2>

</sect1>