lfs-book/chapter06/devices.xml

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<sect1 id="ch-system-devices" xreflabel="devices">
<title>Populating /dev with device nodes</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>Now use the provided udevstart utility to create the initial devices based on
all the information in <filename class="directory">/sys</filename>:</para>

<screen><userinput>/tools/sbin/udevstart</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>
</sect2>


</sect1>