mirror of
https://git.linuxfromscratch.org/lfs.git
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117 lines
4.6 KiB
XML
117 lines
4.6 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>
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<title>Creating Initial Device Nodes</title>
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<para>When the kernel boots the system, it requires the presence of a few
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device nodes, in particular the <filename
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class="devicefile">console</filename> and <filename
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class="devicefile">null</filename> devices. The device nodes must be
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created on the hard disk so that they are available before the kernel
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populates <systemitem class="filesystem">/dev</systemitem>), and
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additionally when Linux is started with
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<parameter>init=/bin/bash</parameter>. Create the devices by running the
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following commands:</para>
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<screen><userinput>mknod -m 600 $LFS/dev/console c 5 1
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mknod -m 666 $LFS/dev/null c 1 3</userinput></screen>
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</sect2>
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<sect2 id="ch-tools-bindmount">
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<title>Mounting and Populating /dev</title>
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<para>The recommended method of populating the <filename
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class="directory">/dev</filename> directory with devices is to mount a
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virtual filesystem (such as <systemitem
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class="filesystem">tmpfs</systemitem>) on the <filename
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class="directory">/dev</filename> directory, and allow the devices to be
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created dynamically on that virtual filesystem as they are detected or
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accessed. Device creation is generally done during the boot process
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by Udev. Since this new system does not yet have Udev and has not yet
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been booted, it is necessary to mount and populate <filename
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class="directory">/dev</filename> manually. This is accomplished by bind
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mounting the host system's <filename class="directory">/dev</filename>
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directory. A bind mount is a special type of mount that allows you to
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create a mirror of a directory or mount point to some other location. Use
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the following 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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