lfs-book/chapter06/mountproc.xml

<sect1 id="ch-system-proc">
<title>Mounting the proc and devpts file systems</title>
<?dbhtml filename="proc.html" dir="chapter06"?>

<para>In order for certain programs to function properly, the
<emphasis>proc</emphasis> and <emphasis>devpts</emphasis> file systems must be
available within the chroot environment. The proc file system is the process
information pseudo file system through which the kernel provides information
about the status of the system. And the devpts file system is nowadays the most
common way pseudo terminals (PTYs) are implemented. Since kernel version 2.4, a
file system can be mounted as many times and in as many places as you like,
thus it's not a problem that these file systems are already mounted on your
host system, especially so because they are virtual file systems.</para>

<para>First become <emphasis>root</emphasis>, as only <emphasis>root</emphasis>
can mount file systems in unusual places. Then check again that the LFS
environment variable is set correctly by running <userinput>echo
$LFS</userinput> and making sure it shows the path to your LFS partition's
mount point, which is <filename class="directory">/mnt/lfs</filename> if you
followed our example.</para>

<para>Now make the mount points for these filesystems:</para>

<screen><userinput>mkdir -p $LFS/{proc,dev/pts}</userinput></screen>

<para>Mount the <emphasis>proc</emphasis> file system with:</para>

<screen><userinput>mount proc $LFS/proc -t proc</userinput></screen>

<para>And mount the <emphasis>devpts</emphasis> file system with:</para>

<screen><userinput>mount devpts $LFS/dev/pts -t devpts</userinput></screen>

<para>This last command might fail with an error like:</para>

<blockquote><screen>filesystem devpts not supported by kernel</screen></blockquote>

<para>The most likely cause for this is that your host system's kernel was
compiled without support for the devpts file system. You can check which file
systems your kernel supports by peeking into its internals with
<command>cat /proc/filesystems</command>. If a file system type named
<emphasis>devfs</emphasis> is listed there, then we'll be able to work around
the problem by mounting the host's devfs file system on top of the new
<filename>/dev</filename> structure which we'll create later on in the section
on <xref linkend="ch-system-MAKEDEV"/>. If devfs was not listed, do not worry
because there is yet a third way to get PTYs working inside the chroot
environment. We'll cover this shortly in the aforementioned
<xref linkend="ch-system-MAKEDEV"/> section.</para>

<para>Remember that if for any reason you stop working on your LFS, and start
again later, it's important to check that these file systems are mounted again
before entering the chroot environment, otherwise problems could occur.</para>

</sect1>