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89 lines
3.2 KiB
XML
89 lines
3.2 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 /{proc,sys,run}</userinput></screen>
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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>The kernel has already mounted
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<systemitem class="filesystem">devtmpfs</systemitem>.
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Mount the remaining virtual kernel filesystems:</para>
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<screen><userinput>mkdir -pv /dev/{pts,shm}
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mount -vt devpts /dev/pts /dev/pts -o gid=5,mode=620
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mount -vt proc proc /proc
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mount -vt sysfs sysfs /sys
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mount -vt tmpfs tmpfs /run
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mount -vt tmpfs tmpfs /dev/shm</userinput></screen>
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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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</sect2>
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<sect2 id="ch-tools-devadjust">
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<title>Adjusting devtmpfs</title>
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<para>Now <systemitem class='filesystem'>proc</systemitem> filesystem
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is mounted, we can replace the device nodes for standard I/O streams
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with symlinks to pseudo files in
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<filename class="directory">/proc/self/fd</filename> (which are symlinks
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to the files connected to the standard I/O streams for the current
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process). This is necessary for I/O redirection in the building system
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of some packages to function properly:</para>
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<screen><userinput>ln -sfv /proc/self/fd/0 /dev/stdin
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ln -sfv /proc/self/fd/1 /dev/stdout
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ln -sfv /proc/self/fd/2 /dev/stderr</userinput></screen>
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</sect2>
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</sect1>
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