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cross-ng: chapter 7: adjust introduction for cross build
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Xi Ruoyao
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@ -64,31 +64,16 @@
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<itemizedlist>
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<listitem>
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<para>The /mnt/lfs partition must be mounted.</para>
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<para>You must boot the temporary system on the target machine.</para>
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</listitem>
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<listitem>
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<para>A few operations, from <quote>Changing Ownership</quote> to
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<quote>Entering the Chroot Environment</quote> must be done as the
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<systemitem class="username">root</systemitem> user, with the LFS
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environment variable set for the
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<para>A few operations, from
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<quote>Preparing Virtual Kernel File Systems</quote> to
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<quote>Setting up Environment</quote> must be done as the
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<systemitem class="username">root</systemitem> user.</para>
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</listitem>
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<listitem>
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<para> When entering chroot, the LFS environment variable must be set
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for <systemitem class="username">root</systemitem>. The LFS
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variable is not used afterwards.</para>
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</listitem>
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<listitem>
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<para> The virtual file systems must be mounted. This can be done
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before or after entering chroot by changing to a host virtual terminal
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and, as <systemitem class="username">root</systemitem>, running the
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commands in
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<xref linkend='ch-tools-bindmount'/> and
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<xref linkend='ch-tools-kernfsmount'/>.</para>
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</listitem>
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</itemizedlist>
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</sect2>
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</sect1>
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@ -9,10 +9,10 @@
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<?dbhtml dir="chapter07"?>
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<?dbhtml filename="chapter07.html"?>
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<title>Entering Chroot and Building Additional Temporary Tools</title>
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<title>Booting the Target System and Building Additional Temporary Tools</title>
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<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="introduction.xml"/>
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<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="changingowner.xml"/>
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<!--xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="changingowner.xml"/-->
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<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="kernfs.xml"/>
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<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="chroot.xml"/>
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<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="creatingdirs.xml"/>
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@ -6,45 +6,58 @@
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]>
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<sect1 id="ch-tools-chroot">
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<?dbhtml filename="chroot.html"?>
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<?dbhtml filename="env.html"?>
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<title>Entering the Chroot Environment</title>
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<title>Setting up the Environment</title>
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<para>Now that all the packages which are required to build the rest of the
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needed tools are on the system, it is time to enter the chroot environment to
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finish installing the remaining temporary tools. This environment will be in
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use also for installing the final system. As user <systemitem
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class="username">root</systemitem>, run the following command to enter the
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environment that is, at the moment, populated with only the temporary
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tools:</para>
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<para>The standard I/O streams of the initial shell process is connected
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with <filename>/dev/console</filename>. However, the testsuite of some
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packages may expect the standard I/O streams to be connected with a
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<quote>real</quote> TTY device node. Spawn a new shell process on the
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TTY device with <command>agetty</command>:</para>
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<screen role="nodump"><userinput>chroot "$LFS" /usr/bin/env -i \
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<screen role="nodump"><userinput>agetty -n -l /bin/bash <replaceable>tty0</replaceable></userinput></screen>
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<para>If you are working via a serial console, replace
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<replaceable>tty0</replaceable> with the name of the serial console
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device node, for example <literal>ttyS0</literal>.</para>
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<para>The command above spawns a new shell process on the TTY device
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specified in the command, and the initial shell process will run in
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background as an init process with very limited functions. The new shell
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process will output:</para>
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<screen role="nodump"><computeroutput>bash: cannot set terminal process group (-1): Inappropriate ioctl for device
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bash: no job control in this shell</computeroutput></screen>
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<para>This is normal because the shell is not assigned with a
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controlling terminal yet. Now set up controlling terminal and
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environment variables:</para>
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<screen><userinput>exec setsid -c /usr/bin/env -i \
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HOME=/root \
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TERM="$TERM" \
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PS1='(lfs chroot) \u:\w\$ ' \
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PS1='(lfs) \u:\w\$ ' \
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PATH=/usr/bin:/usr/sbin \
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/bin/bash --login</userinput></screen>
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<para>The command replace the current shell process with a new shell
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process, with controlling terminal set up.</para>
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<para>The <parameter>-i</parameter> option given to the <command>env</command>
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command will clear all variables of the chroot environment. After that, only
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command will clear all variables of the environment. After that, only
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the <envar>HOME</envar>, <envar>TERM</envar>, <envar>PS1</envar>, and
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<envar>PATH</envar> variables are set again. The
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<parameter>TERM=$TERM</parameter> construct will set the <envar>TERM</envar>
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variable inside chroot to the same value as outside chroot. This variable is
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variable to the default value specified by <command>agetty</command>. This variable is
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needed for programs like <command>vim</command> and <command>less</command>
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to operate properly. If other variables are desired, such as
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<envar>CFLAGS</envar> or <envar>CXXFLAGS</envar>, this is a good place to set
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them again.</para>
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<para>From this point on, there is no need to use the
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<envar>LFS</envar> variable anymore because all work will be restricted
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to the LFS file system. This is because the Bash shell is told that
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<filename class="directory">$LFS</filename> is now the root
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(<filename class="directory">/</filename>) directory.</para>
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<para>Notice that <filename class="directory">/tools/bin</filename> is not
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in the <envar>PATH</envar>. This means that the cross toolchain will no longer be
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used in the chroot environment.</para>
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used on the target machine.</para>
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<para>Note that the <command>bash</command> prompt will say
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<computeroutput>I have no name!</computeroutput> This is normal because the
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@ -52,12 +65,12 @@
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<note>
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<para>It is important that all the commands throughout the remainder of this
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chapter and the following chapters are run from within the chroot
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environment. If you leave this environment for any reason (rebooting for
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chapter and the following chapters are run from within the environment
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we've set. If you leave this environment for any reason (rebooting for
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example), ensure that the virtual kernel filesystems are mounted as
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explained in <xref linkend="ch-tools-bindmount"/> and <xref
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linkend="ch-tools-kernfsmount"/> and enter chroot again before continuing
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with the installation.</para>
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explained in <xref linkend="ch-tools-kernfsmount"/> and
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<xref linkend="ch-tools-devadjust"/> and set up the environment again before
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continuing with the installation.</para>
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</note>
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</sect1>
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@ -12,21 +12,21 @@
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<para>This chapter shows how to build the last missing bits of the temporary
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system: the tools needed by the build machinery of various packages. Now
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that all circular dependencies have been resolved, a <quote>chroot</quote>
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environment, completely isolated from the host operating system (except for
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the running kernel), can be used for the build.</para>
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that all circular dependencies have been resolved and the temporary system
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is already bootable, we can boot it on the target machine and it would be
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completely isolated from the host operating system. Then we can continue
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to build on the target machine.</para>
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<para>For proper operation of the isolated environment, some communication
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<para>For proper operation of the temporary system, some communication
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with the running kernel must be established. This is done through the
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so-called <emphasis>Virtual Kernel File Systems</emphasis>, which must be
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mounted when entering the chroot environment. You may want to check
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that they are mounted by issuing <command>findmnt</command>.</para>
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mounted as soon as possible after boot. You may want to check
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that they are mounted by issuing <command>mount</command>.</para>
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<para>Until <xref linkend="ch-tools-chroot"/>, the commands must be
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run as <systemitem class="username">root</systemitem>, with the
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<envar>LFS</envar> variable set. After entering chroot, all commands
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are run as root, fortunately without access to the OS of the computer
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you built LFS on. Be careful anyway, as it is easy to destroy the whole
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LFS system with badly formed commands.</para>
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<para>All commands in this and following chapters are run as root on the
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target system, fortunately without access to the host system.
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Be careful anyway, as if the storage devices of your target system already
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contain some important data, it's possible to destroy them with badly
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formed commands.</para>
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</sect1>
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@ -22,58 +22,22 @@
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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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<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>Now mount the remaining virtual kernel filesystems:</para>
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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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<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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@ -101,15 +65,23 @@ mount -vt tmpfs tmpfs $LFS/run</userinput></screen>
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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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<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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