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119 lines
4.9 KiB
XML
119 lines
4.9 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>Applications running in user space utilize various file
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systems exported by the kernel to communicate
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with the kernel itself. These file systems are virtual: no disk
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space is used for them. The content of the file systems resides in
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memory. These file systems must be mounted in the $LFS directory tree
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so the applications can find them in the chroot environment.</para>
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<para>Begin by creating directories on which the file systems will be
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mounted:</para>
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<screen><userinput>mkdir -pv $LFS/{dev,proc,sys,run}</userinput></screen>
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<sect2 id="ch-tools-bindmount">
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<title>Mounting and Populating /dev</title>
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<para>During a normal boot of the LFS system, the kernel automatically
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mounts the <systemitem class="filesystem">devtmpfs</systemitem>
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filesystem on the
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<filename class="directory">/dev</filename> directory; the kernel
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creates device nodes on that virtual filesystem during the boot process
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or when a device is first detected or accessed. The udev daemon may
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change the owner or permission of the device nodes created by the
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kernel, or create new device nodes or symlinks to ease the work of
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distro maintainers or system administrators. (See
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<xref linkend='ch-config-udev-device-node-creation'/> for details.)
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If the host kernel supports &devtmpfs;, we can simply mount a
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&devtmpfs; at <filename class='directory'>$LFS/dev</filename> and rely
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on the kernel to populate it (the LFS building process does not need
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the additional work onto &devtmpfs; by udev daemon).</para>
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<para>But, some host kernels may lack &devtmpfs; support and these
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host distros maintain the content of
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<filename class="directory">/dev</filename> with different methods.
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So the only host-agnostic way for populating
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<filename class="directory">$LFS/dev</filename> is
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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 at some other location. Use the following
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command to do 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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<para>In other host systems <filename>/dev/shm</filename> is a mount point
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for a tmpfs. In that case the mount of /dev above will only create
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/dev/shm as a directory in the chroot environment. In this situation
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we must explicitly mount a tmpfs:</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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else
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mount -t tmpfs -o nosuid,nodev tmpfs $LFS/dev/shm
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fi</userinput></screen>
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</sect2>
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</sect1>
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