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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.</para>
<para>Begin by creating the directories on which these virtual file systems will be
mounted:</para>
<screen><userinput>mkdir -pv /{proc,sys,run}</userinput></screen>
<sect2 id="ch-tools-kernfsmount">
<title>Mounting Virtual Kernel File Systems</title>
<para>The kernel has already mounted
<systemitem class="filesystem">devtmpfs</systemitem>.
Mount the remaining virtual kernel file systems:</para>
<screen><userinput>mkdir -pv /dev/{pts,shm}
mount -vt devpts /dev/pts /dev/pts -o gid=5,mode=620
mount -vt proc proc /proc
mount -vt sysfs sysfs /sys
mount -vt tmpfs tmpfs /run
mount -vt tmpfs tmpfs /dev/shm -o nosuid,nodev</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>
</sect2>
<sect2 id="ch-tools-devadjust">
<title>Adjusting devtmpfs</title>
<para>Now <systemitem class='filesystem'>proc</systemitem> filesystem
is mounted, we can replace the device nodes for standard I/O streams
with symlinks to pseudo files in
<filename class="directory">/proc/self/fd</filename> (which are symlinks
to the files connected to the standard I/O streams for the current
process). And, create another symlink recommended by the kernel
documentation. These are necessary for I/O redirection in the building
system of some packages to function properly:</para>
<screen><userinput>ln -sfv /proc/self/fd/0 /dev/stdin
ln -sfv /proc/self/fd/1 /dev/stdout
ln -sfv /proc/self/fd/2 /dev/stderr
ln -sv /proc/self/fd /dev</userinput></screen>
</sect2>
</sect1>
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