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<?xml version="1.0" encoding="ISO-8859-1"?>
<!DOCTYPE sect1 PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
"http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [
<!ENTITY % general-entities SYSTEM "../general.ent">
%general-entities;
]>
<sect1 id="ch-system-kernfs">
<?dbhtml filename="kernfs.html"?>
<title>Preparing Virtual Kernel File Systems</title>
<indexterm zone="ch-system-kernfs">
<primary sortas="e-/dev/">/dev/*</primary>
</indexterm>
<para>Various file systems exported by the kernel are used to communicate to
and from the kernel itself. These file systems are virtual in that no disk
space is used for them. The content of the file systems resides in
memory.</para>
<para>Begin by creating directories onto which the file systems will be
mounted:</para>
<screen><userinput>mkdir -v $LFS/{dev,proc,sys}</userinput></screen>
<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. The device nodes must be created
on the hard disk so that they are available before <command>udevd</command>
has been started, and additionally when Linux is started with
<parameter>init=/bin/bash</parameter>. Create the devices by running the
following commands:</para>
<screen><userinput>mknod -m 600 $LFS/dev/console c 5 1
mknod -m 666 $LFS/dev/null c 1 3</userinput></screen>
</sect2>
<sect2 id="ch-system-bindmount">
<title>Mounting 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">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. Device creation is generally done during the boot process
by Udev. Since this new system does not yet have Udev and has not yet
been booted, it is necessary to mount and populate <filename
class="directory">/dev</filename> 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 to some other location. Use
the following command to achieve this:</para>
<screen><userinput>mount -v --bind /dev $LFS/dev</userinput></screen>
</sect2>
<sect2 id="ch-system-kernfsmount">
<title>Mounting Virtual Kernel File Systems</title>
<para>Now mount the remaining virtual kernel filesystems:</para>
<screen><userinput>mount -vt devpts devpts $LFS/dev/pts
mount -vt proc proc $LFS/proc
mount -vt sysfs sysfs $LFS/sys</userinput></screen>
<para>In some host systems, <filename>/dev/shm</filename> is a
symbolic link to <filename class="directory">/run/shm</filename>.
Inside a chroot envirnment, this symbolic link needs to be
changed to a normal directory before mounting as a temporary
file system:</para>
<screen><userinput>if [ -h /dev/shm ]; then
rm -f $LFS/dev/shm
mkdir $LFS/dev/shm
fi
mount -vt tmpfs shm $LFS/dev/shm</userinput></screen>
</sect2>
</sect1>
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