lfs-book/chapter06/devices.xml

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<sect1 id="ch-system-devices" xreflabel="devices">
<title>Populating /dev</title>
<?dbhtml filename="devices.html"?>

<indexterm zone="ch-system-devices"><primary sortas="e-Devices">Devices</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:</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 ramfs and populating /dev</title>

<para>The ideal way to populate <filename class="directory">/dev</filename> is
to mount a <systemitem class="filesystem">ramfs</systemitem> onto <filename class="directory">/dev </filename>
like <systemitem class="filesystem">tmpfs</systemitem>, but it
cannot be swapped) and create the devices on there during each bootup.  Since we haven't
booted the system, we have to do what the bootscripts would otherwise do for us, and
populate <filename class="directory">/dev</filename> ourselves.  Begin by mounting <filename class="directory">/dev</filename>:</para>

<screen><userinput>mount -n -t ramfs none /dev</userinput></screen>

<para>Since we do not have the Udev package installed yet, we'll create a
minimal set of device nodes to use for building:</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 root:tty /dev/{console,ptmx,tty}</userinput></screen>

<para>There are some symlinks and directories required by LFS that are not created by
Udev, so we create those ourselves here:</para>

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

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

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