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ce11e97f01
IIRC we switched from separate devpts to bind mount, and matched the UID of tester with the host UID owning the TTY, to satisify the Bash test suite. But now we are always using UID 101 for tester and expect to spawn a PTY for Bash test suite (so when building LFS in a TTY owned by the root user of the host tester won't be UID 0). Thus we can switch back to a separate devpts mount which is cleaner and safer. And we are already using a separate devpts mount in Chapter 11.
122 lines
5.0 KiB
XML
122 lines
5.0 KiB
XML
<?xml version="1.0" encoding="UTF-8"?>
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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 userspace utilize various file
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systems created 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 these 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 the directories on which these virtual file systems will be
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mounted:</para>
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<screen><userinput>mkdir -pv $LFS/{dev,proc,sys,run}</userinput></screen>
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<sect2 id="ch-tools-bindmount">
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<title>Mounting and Populating /dev</title>
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<para>During a normal boot of an LFS system, the kernel automatically
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mounts the <systemitem class="filesystem">devtmpfs</systemitem>
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file system on the
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<filename class="directory">/dev</filename> directory; the kernel
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creates device nodes on that virtual file system during the boot process,
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or when a device is first detected or accessed. The udev daemon may
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change the ownership or permissions of the device nodes created by the
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kernel, and create new device nodes or symlinks, to ease the work of
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distro maintainers and system administrators. (See
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<xref linkend='ch-config-udev-device-node-creation'/> for details.)
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If the host kernel supports &devtmpfs;, we can simply mount a
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&devtmpfs; at <filename class='directory'>$LFS/dev</filename> and rely
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on the kernel to populate it.</para>
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<para>But some host kernels lack &devtmpfs; support; these
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host distros use different methods to create the content of
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<filename class="directory">/dev</filename>.
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So the only host-agnostic way to populate the
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<filename class="directory">$LFS/dev</filename> directory is
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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 makes a directory subtree or a file
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visible 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 file systems:</para>
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<!-- Do not put any option after $LFS/${mountpoint} or jhalfs cannot
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handle it! -->
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<screen><userinput>mount -vt devpts devpts -o gid=5,mode=0620 $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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<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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<para>In some host systems, <filename>/dev/shm</filename> is a
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symbolic link to a directory, typically
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<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 with the correct permissions.</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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install -v -d -m 1777 $LFS$(realpath /dev/shm)
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else
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mount -vt 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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