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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-tools-kernfs">
<?dbhtml filename="kernfs.html"?>
<title>Preparing Virtual Kernel File Systems</title>
<indexterm zone="ch-tools-kernfs">
<primary sortas="e-/dev/">/dev/*</primary>
</indexterm>
<para>Applications running in userspace utilize various file
systems created by the kernel to communicate
with the kernel itself. These file systems are virtual: no disk
space is used for them. The content of these file systems resides in
memory. These file systems must be mounted in the $LFS directory tree
so the applications can find them in the chroot environment.</para>
<para>Begin by creating the directories on which these virtual file systems will be
mounted:</para>
<screen><userinput>mkdir -pv $LFS/{dev,proc,sys,run}</userinput></screen>
<sect2 id="ch-tools-bindmount">
<title>Mounting and Populating /dev</title>
<para>During a normal boot of an LFS system, the kernel automatically
mounts the <systemitem class="filesystem">devtmpfs</systemitem>
file system on the
<filename class="directory">/dev</filename> directory; the kernel
creates device nodes on that virtual file system during the boot process,
or when a device is first detected or accessed. The udev daemon may
change the ownership or permissions of the device nodes created by the
kernel, and create new device nodes or symlinks, to ease the work of
distro maintainers and system administrators. (See
<xref linkend='ch-config-udev-device-node-creation'/> for details.)
If the host kernel supports &devtmpfs;, we can simply mount a
&devtmpfs; at <filename class='directory'>$LFS/dev</filename> and rely
on the kernel to populate it.</para>
<para>But some host kernels lack &devtmpfs; support; these
host distros use different methods to create the content of
<filename class="directory">/dev</filename>.
So the only host-agnostic way to populate the
<filename class="directory">$LFS/dev</filename> directory is
by bind mounting the host system's
<filename class="directory">/dev</filename> directory. A bind mount is
a special type of mount that makes a directory subtree or a file
visible at some other location. Use the following
command to do this.</para>
<screen><userinput>mount -v --bind /dev $LFS/dev</userinput></screen>
</sect2>
<sect2 id="ch-tools-kernfsmount">
<title>Mounting Virtual Kernel File Systems</title>
<para>Now mount the remaining virtual kernel file systems:</para>
<screen><userinput>mount -v --bind /dev/pts $LFS/dev/pts
mount -vt proc proc $LFS/proc
mount -vt sysfs sysfs $LFS/sys
mount -vt tmpfs tmpfs $LFS/run</userinput></screen>
<!--
<variablelist>
<title>The meaning of the mount options for devpts:</title>
<varlistentry>
<term><parameter>gid=5</parameter></term>
<listitem>
<para>This ensures that all devpts-created device nodes are owned by
group ID 5. This is the ID we will use later on for the <systemitem
class="groupname">tty</systemitem> group. We use the group ID instead
of a name, since the host system might use a different ID for its
<systemitem class="groupname">tty</systemitem> group.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>mode=0620</parameter></term>
<listitem>
<para>This ensures that all devpts-created device nodes have mode 0620
(user readable and writable, group writable). Together with the
option above, this ensures that devpts will create device nodes that
meet the requirements of grantpt(), meaning the Glibc
<command>pt_chown</command> helper binary (which is not installed by
default) is not necessary.</para>
</listitem>
</varlistentry>
</variablelist>
-->
<para>In some host systems, <filename>/dev/shm</filename> is a
symbolic link to <filename class="directory">/run/shm</filename>.
The /run tmpfs was mounted above so in this case only a
directory needs to be created.</para>
<para>In other host systems <filename>/dev/shm</filename> is a mount point
for a tmpfs. In that case the mount of /dev above will only create
/dev/shm as a directory in the chroot environment. In this situation
we must explicitly mount a tmpfs:</para>
<screen><userinput>if [ -h $LFS/dev/shm ]; then
mkdir -pv $LFS/$(readlink $LFS/dev/shm)
else
mount -vt tmpfs -o nosuid,nodev tmpfs $LFS/dev/shm
fi</userinput></screen>
</sect2>
</sect1>
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