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devtmpfs already contains many device nodes created by the kernel once it's mounted, and Udev creates or renames nodes based on kernel work.
99 lines
3.8 KiB
XML
99 lines
3.8 KiB
XML
<?xml version="1.0" encoding="ISO-8859-1"?>
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<!DOCTYPE sect1 PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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"http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [
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<!ENTITY % general-entities SYSTEM "../general.ent">
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%general-entities;
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]>
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<sect1 id="ch-tools-kernfs">
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<?dbhtml filename="kernfs.html"?>
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<title>Preparing Virtual Kernel File Systems</title>
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<indexterm zone="ch-tools-kernfs">
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<primary sortas="e-/dev/">/dev/*</primary>
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</indexterm>
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<para>Various file systems exported by the kernel are used to communicate to
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and from the kernel itself. These file systems are virtual in that no disk
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space is used for them. The content of the file systems resides in
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memory.</para>
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<para>Begin by creating directories onto which the file systems will be
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mounted:</para>
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<screen><userinput>mkdir -pv $LFS/{dev,proc,sys,run}</userinput></screen>
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<sect2 id="ch-tools-bindmount">
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<title>Mounting and Populating /dev</title>
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<para>During a normal boot, the kernel automatically mounts the
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<systemitem class="filesystem">devtmpfs</systemitem> filesystem on the
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<filename class="directory">/dev</filename> directory, and allow the
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devices to be created dynamically on that virtual filesystem as they
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are detected or accessed. Device creation is generally done during the
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boot process by the kernel and Udev.
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Since this new system does not yet have Udev and
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has not yet been booted, it is necessary to mount and populate
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<filename class="directory">/dev</filename> manually. This is
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accomplished by bind mounting the host system's
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<filename class="directory">/dev</filename> directory. A bind mount is
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a special type of mount that allows you to create a mirror of a
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directory or mount point to some other location. Use the following
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command to achieve this:</para>
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<screen><userinput>mount -v --bind /dev $LFS/dev</userinput></screen>
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</sect2>
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<sect2 id="ch-tools-kernfsmount">
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<title>Mounting Virtual Kernel File Systems</title>
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<para>Now mount the remaining virtual kernel filesystems:</para>
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<screen><userinput>mount -v --bind /dev/pts $LFS/dev/pts
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mount -vt proc proc $LFS/proc
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mount -vt sysfs sysfs $LFS/sys
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mount -vt tmpfs tmpfs $LFS/run</userinput></screen>
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<!--
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<variablelist>
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<title>The meaning of the mount options for devpts:</title>
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<varlistentry>
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<term><parameter>gid=5</parameter></term>
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<listitem>
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<para>This ensures that all devpts-created device nodes are owned by
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group ID 5. This is the ID we will use later on for the <systemitem
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class="groupname">tty</systemitem> group. We use the group ID instead
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of a name, since the host system might use a different ID for its
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<systemitem class="groupname">tty</systemitem> group.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>mode=0620</parameter></term>
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<listitem>
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<para>This ensures that all devpts-created device nodes have mode 0620
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(user readable and writable, group writable). Together with the
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option above, this ensures that devpts will create device nodes that
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meet the requirements of grantpt(), meaning the Glibc
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<command>pt_chown</command> helper binary (which is not installed by
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default) is not necessary.</para>
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</listitem>
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</varlistentry>
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</variablelist>
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-->
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<para>In some host systems, <filename>/dev/shm</filename> is a
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symbolic link to <filename class="directory">/run/shm</filename>.
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The /run tmpfs was mounted above so in this case only a
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directory needs to be created.</para>
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<screen><userinput>if [ -h $LFS/dev/shm ]; then
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mkdir -pv $LFS/$(readlink $LFS/dev/shm)
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fi</userinput></screen>
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</sect2>
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</sect1>
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