lfs-book/chapter06/devices.xml

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

<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. Create these 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 ramfs 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">ramfs</systemitem> or
<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 bootscripts would otherwise do by
mounting <filename class="directory">/dev</filename>:</para>

<screen><userinput>mount -n -t ramfs 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 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 create those 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
newly-created directories:</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>