Added a few comments here and there

[linux_from_scratch.git] / BOOK / chapter06 / chapter06.xml

<chapter id="chapter-building-system" xreflabel="Chapter 6">
<title>Installing basic system software</title>
<?dbhtml filename="chapter06.html" dir="chapter06"?>


<sect1 id="ch-system-introduction">
<title>Introduction</title>
<?dbhtml filename="introduction.html" dir="chapter06"?>

<para>In this chapter we enter the building site, and start
constructing our LFS system in earnest. That is, we chroot into
our temporary mini Linux system, create some auxiliary things,
and then start installing all the packages, one by one.</para>
 
<para>The installation of all this software is pretty straightforward,
and you will probably think it would be much shorter to give here
the generic installation instructions and explain in full only the
installation of those packages that require an alternate method.
Although we agree with that, we nevertheless choose to give the 
full instructions for each and every package, simply to minimize
the possibilities for mistakes.</para>

<para>The key to learning what makes a Linux system work is to know
what each package is used for and why the user (or the system) needs it.
For this purpose for every installed package a summary of its content is
given followed by concise descriptions of each program and library it
installed.</para>

<para>If you plan to use compiler optimizations in this chapter, take a look at
the optimization hint at <ulink url="&hints-root;optimization.txt"/>. Compiler
optimizations can make a program run slightly faster, but they may also cause
compilation difficulties and even problems when running the program. If a
package refuses to compile when using optimization, try to compile it without
optimization and see if the problem goes away. Even if the package does compile
when using optimization, there is the risk it may have been compiled incorrectly
due to complex interactions between the code and build tools. In short, the
small potential gains achieved in using compiler optimization are generally
outweighed by the risk. First time builders of LFS are encouraged to build
without custom optimizations. Your system will still be very fast and very
stable at the same time.</para>

<para>The order in which packages are installed in this chapter has
to be strictly followed, to ensure that no program gets a path referring
to <filename class="directory">/tools</filename> hard-wired into it.
For the same reason, <emphasis>do not </emphasis> compile packages
in parallel. Compiling in parallel may save you some time (especially on
dual-CPU machines), but it could result in a program containing a
hard-wired path to <filename class="directory">/tools</filename>,
which will cause the program to stop working when that directory
is removed.</para>

<para>Before the installation instructions each installation page gives some
information about the package: a concise description of what it contains, how
long it will approximately take to build it, how much disk space it needs
during this building process, the official download location of the package
(in case you just want to update a few of them), and which other packages it
needs in order to be built successfully. After the installation instructions
follows a list of programs and libraries that the package installs, together
with a series of short descriptions of these.</para>

</sect1>

&c6-mountproc;

<sect1 id="ch-system-chroot">
<title>Entering the chroot environment</title>
<?dbhtml filename="chroot.html" dir="chapter06"?>

<para>It is time to enter the chroot environment in order to begin building
and installing your final LFS system.</para>

<para>First check, just like earlier, that the LFS environment variable is set
up properly by running <userinput>echo $LFS</userinput> and making sure it
shows the path to your LFS partition's mount point, which is
<filename class="directory">/mnt/lfs</filename> if you followed our example.</para>

<para>As <emphasis>root</emphasis>, run the following command to enter the
chroot environment:</para>

<screen><userinput>chroot $LFS /tools/bin/env -i \
&nbsp;&nbsp;&nbsp;&nbsp;HOME=/root TERM=$TERM PS1='\u:\w\$ ' \
&nbsp;&nbsp;&nbsp;&nbsp;PATH=/bin:/usr/bin:/sbin:/usr/sbin:/tools/bin \
&nbsp;&nbsp;&nbsp;&nbsp;/tools/bin/bash --login +h</userinput></screen>

<para>The <emphasis>-i</emphasis> option given to the
<command>env</command> command will clear all variables of the chroot
environment. After that, only the HOME, TERM, PS1 and PATH variables are
set again. The TERM=$TERM construct will set the TERM variable inside chroot
to the same value as outside chroot; this variable is needed for programs
like <command>vim</command> and <command>less</command> to operate
properly. If you need other variables present, such as CFLAGS or CXXFLAGS,
this is a good place to set them again.</para>

<para>From this point on there's no need to use the LFS variable anymore,
because everything you do will be restricted to the LFS file system -- since
what the shell thinks is <filename class="directory">/</filename> is actually
the value of <filename class="directory">$LFS</filename>, which was passed to
the chroot command.</para>

<para>Notice that <filename class="directory">/tools/bin</filename> comes
last in the PATH. This means that a temporary tool will not be used any more
as soon as its final version is installed. Well, at least when the shell
doesn't remember the locations of executed binaries -- for this reason hashing
is switched off by passing the <emphasis>+h</emphasis> option to
<command>bash</command>.</para>

<para>You have to make sure all the commands in the rest of this chapter and
in the following chapters are run from within the chroot environment.
If you ever leave this environment for any reason (rebooting for example),
you must remember to first mount the proc and devpts file systems (discussed
in the previous section) <emphasis>and</emphasis> enter chroot again before
continuing with the installations.</para>

<para>Note that the bash prompt will say "I have no name!" This is normal, as
the <filename>/etc/passwd</filename> file has not been created yet.</para>

</sect1>


<sect1 id="ch-system-changingowner">
<title>Changing ownership</title>
<?dbhtml filename="changingowner.html" dir="chapter06"?>

<para>Right now the <filename class="directory">/tools</filename> directory
is owned by the user <emphasis>lfs</emphasis>, a user that exists only on your
host system. Although you will probably want to delete the
<filename class="directory">/tools</filename> directory once you have
finished your LFS system, you may want to keep it around, for example to
build more LFS systems. But if you keep the
<filename class="directory">/tools</filename> directory as it is, you end up
with files owned by a user ID without a corresponding account. This is
dangerous because a user account created later on could get this same user ID
and would suddenly own the <filename class="directory">/tools</filename>
directory and all the files therein, thus exposing these files to possible
malicious manipulation.</para>

<para>To avoid this issue, you could add the <emphasis>lfs</emphasis> user to
your new LFS system later on when creating the <filename>/etc/passwd</filename>
file, taking care to assign it the same user and group IDs as on your host
system. Alternatively, you can (and the book assumes you do) assign the
contents of the <filename class="directory">/tools</filename> directory to
user <emphasis>root</emphasis> by running the following command:</para>

<screen><userinput>chown -R 0:0 /tools</userinput></screen>

<para>The command uses "0:0" instead of "root:root", because
<userinput>chown</userinput> is unable to resolve the name "root" until the
password file has been created.</para>

</sect1>


<sect1 id="ch-system-creatingdirs">
<title>Creating directories</title>
<?dbhtml filename="creatingdirs.html" dir="chapter06"?>

<para>Let's now create some structure in our LFS file system. Let's create
a directory tree. Issuing the following commands will create a more or less
standard tree:</para>
 
<screen><userinput>mkdir -p /{bin,boot,dev/{pts,shm},etc/opt,home,lib,mnt,proc}
mkdir -p /{root,sbin,tmp,usr/local,var,opt}
for dirname in /usr /usr/local
&nbsp;&nbsp;&nbsp;&nbsp;do
&nbsp;&nbsp;&nbsp;&nbsp;mkdir $dirname/{bin,etc,include,lib,sbin,share,src}
&nbsp;&nbsp;&nbsp;&nbsp;ln -s share/{man,doc,info} $dirname
&nbsp;&nbsp;&nbsp;&nbsp;mkdir $dirname/share/{doc,info,locale,man}
&nbsp;&nbsp;&nbsp;&nbsp;mkdir $dirname/share/{misc,terminfo,zoneinfo}
&nbsp;&nbsp;&nbsp;&nbsp;mkdir $dirname/share/man/man{1,2,3,4,5,6,7,8}
done
mkdir /var/{lock,log,mail,run,spool}
mkdir -p /var/{tmp,opt,cache,lib/misc,local}
mkdir /opt/{bin,doc,include,info}
mkdir -p /opt/{lib,man/man{1,2,3,4,5,6,7,8}}</userinput></screen>

<para>Directories are, by default, created with permission mode 755, but this
isn't desirable for all directories. We will make two changes: one to the home
directory of <emphasis>root</emphasis>, and another to the directories for
temporary files.</para>

<screen><userinput>chmod 0750 /root
chmod 1777 /tmp /var/tmp</userinput></screen>

<para>The first mode change ensures that not just anybody can enter the
<filename class="directory">/root</filename> directory -- the same
as a normal user would do with his or her home directory.
The second mode change makes sure that any user can write to the
<filename class="directory">/tmp</filename> and
<filename class="directory">/var/tmp</filename> directories, but
cannot remove other users' files from them. The latter is prohibited
by the so-called "sticky bit" -- the highest bit in the 1777 bit mask.</para>

<sect2>
<title>FHS compliance note</title>

<para>We have based our directory tree on the FHS standard (available at
<ulink url="http://www.pathname.com/fhs/"/>). Besides the above created
tree this standard stipulates the existence of
<filename class="directory">/usr/local/games</filename> and
<filename class="directory">/usr/share/games</filename>, but we don't
much like these for a base system. However, feel free to make your system
FHS-compliant. As to the structure of the
<filename class="directory">/usr/local/share</filename> subdirectory, the FHS
isn't precise, so we created here the directories that we think are needed.</para>

</sect2>

</sect1>


<sect1 id="ch-system-createfiles">
<title>Creating essential symlinks</title>
<?dbhtml filename="createfiles.html" dir="chapter06"?>

<para>Some programs hard-wire paths to programs which don't exist yet. In
order to satisfy these programs, we create a number of symbolic links which
will be replaced by real files throughout the course of this chapter when
we're installing all the software.</para>

<screen><userinput>ln -s /tools/bin/{bash,cat,pwd,stty} /bin
ln -s /tools/bin/perl /usr/bin
ln -s /tools/lib/libgcc_s.so.1 /usr/lib
ln -s bash /bin/sh</userinput></screen>

</sect1>


<sect1 id="ch-system-pwdgroup">
<title>Creating the passwd, group and log files</title>
<?dbhtml filename="pwdgroup.html" dir="chapter06"?>

<para>In order for <emphasis>root</emphasis> to be able to login and for the 
name "root" to be recognized, there need to be relevant entries in the 
<filename>/etc/passwd</filename> and <filename>/etc/group</filename> files.</para>

<para>Create the <filename>/etc/passwd</filename> file by running the following 
command:</para>

<screen><userinput>cat &gt; /etc/passwd &lt;&lt; "EOF"</userinput>
root:x:0:0:root:/root:/bin/bash
<userinput>EOF</userinput></screen>

<para>The actual password for <emphasis>root</emphasis> (the "x" here is just a 
placeholder) will be set later.</para>

<para>Create the <filename>/etc/group</filename> file by running the following 
command:</para>

<screen><userinput>cat &gt; /etc/group &lt;&lt; "EOF"</userinput>
root:x:0:
bin:x:1:
sys:x:2:
kmem:x:3:
tty:x:4:
tape:x:5:
daemon:x:6:
floppy:x:7:
disk:x:8:
lp:x:9:
dialout:x:10:
audio:x:11:
<userinput>EOF</userinput></screen>

<para>The created groups aren't part of any standard -- they are the groups 
that the MAKEDEV script in the next section uses. Besides the group "root", the 
LSB (<ulink url="http://www.linuxbase.org"/>) recommends only a group "bin", 
with a GID of 1, be present. All other group names and GIDs can be chosen 
freely by the user, as well-written packages don't depend on GID numbers but 
use the group's name.</para>

<para>To get rid of the "I have no name!" prompt, we will start a new shell.
Since we installed a full Glibc in <xref linkend="chapter-temporary-tools"/>, and have just
created the <filename>/etc/passwd</filename> and
<filename>/etc/group</filename> files, user name and group name resolution
will now work.</para>

<screen><userinput>exec /tools/bin/bash --login +h</userinput></screen>

<para>Note the use of the <emphasis>+h</emphasis> directive. This tells
<command>bash</command> not to use its internal path hashing. Without this
directive, <command>bash</command> would remember the paths to binaries it
has executed. Since we want to use our newly compiled binaries as soon as
they are installed, we turn off this function for the duration of this
chapter.</para>

<para>The <command>login</command>, <command>agetty</command> and
<command>init</command> programs (and some others) use a number of log
files to record information such as who was logged into the system and when.
These programs, however, won't write to the log files if they don't already
exist. Initialize the log files and give them their proper permissions:</para>

<screen><userinput>touch /var/run/utmp /var/log/{btmp,lastlog,wtmp}
chmod 644 /var/run/utmp /var/log/{btmp,lastlog,wtmp}</userinput></screen>

<para>The <filename>/var/run/utmp</filename> file records the users that are
currently logged in. The <filename>/var/log/wtmp</filename> file records all
logins and logouts. The <filename>/var/log/lastlog</filename> file records for
each user when he or she last logged in. The <filename>/var/log/btmp</filename>
file records the bad login attempts.</para>

</sect1>


&c6-makedev;
&c6-kernel;
&c6-manpages;
&c6-glibc;


<sect1 id="ch-system-adjustingtoolchain">
<title>Re-adjusting the toolchain</title>
<?dbhtml filename="adjustingtoolchain.html" dir="chapter06"?>

<para>Now that the new C libraries have been installed, it's time to re-adjust
our toolchain. We'll adjust it so that it will link any newly compiled program
against the new C libraries. Basically, this is the reverse of what we did
in the "locking in" stage in the beginning of the previous chapter.</para>

<para>The first thing to do is to adjust the linker. For this we retained the
source and build directories from the second pass over Binutils. Install the
adjusted linker by running the following from within the
<filename class="directory">binutils-build</filename> directory:</para>

<screen><userinput>make -C ld INSTALL=/tools/bin/install install</userinput></screen>

<note><para>If you somehow missed the earlier warning to retain the Binutils
source and build directories from the second pass in
<xref linkend="chapter-temporary-tools"/>, or otherwise accidentally deleted them or just
don't have access to them, don't worry, all is not lost. Just ignore the above
command. The result will be that the next package, Binutils, will link against
the Glibc libraries in <filename class="directory">/tools</filename> rather
than <filename class="directory">/usr</filename>. This is not ideal, however,
our testing has shown that the resulting Binutils program binaries should be
identical.</para></note>

<para>From now on every compiled program will link <emphasis>only</emphasis>
against the libraries in <filename>/usr/lib</filename> and
<filename>/lib</filename>. The extra
<emphasis>INSTALL=/tools/bin/install</emphasis> is needed because the Makefile
created during the second pass still contains the reference to
<filename>/usr/bin/install</filename>, which we obviously haven't installed yet.
Some host distributions contain a <filename class="symlink">ginstall</filename>
symbolic link which takes precedence in the Makefile and thus can cause a
problem here. The above command takes care of this also.</para>

<para>You can now remove the Binutils source and build directories.</para>

<para>The next thing to do is to amend our GCC specs file so that it points
to the new dynamic linker. Just like earlier on, we use a sed to accomplish
this:</para>

<!-- Ampersands are needed to allow cut and paste -->

<screen><userinput>SPECFILE=/tools/lib/gcc-lib/*/*/specs &amp;&amp;
sed -e 's@ /tools/lib/ld-linux.so.2@ /lib/ld-linux.so.2@g' \
&nbsp;&nbsp;&nbsp;&nbsp;$SPECFILE &gt; newspecfile &amp;&amp;
mv -f newspecfile $SPECFILE &amp;&amp;
unset SPECFILE</userinput></screen>

<para>Again, cutting and pasting the above is recommended. And just like
before, it is a good idea to visually inspect the specs file to verify the
intended change was actually made.</para>

<important><para>If you are working on a platform where the name of the dynamic
linker is something other than <filename>ld-linux.so.2</filename>, you
<emphasis>must</emphasis> substitute <filename>ld-linux.so.2</filename> with the
name of your platform's dynamic linker in the above commands. Refer back to
<xref linkend="ch-tools-toolchaintechnotes"/> if necessary.</para></important>

<!-- HACK - Force some whitespace to appease tidy -->
<literallayout></literallayout>

<caution><para>It is imperative at this point to stop and ensure that the
basic functions (compiling and linking) of the adjusted toolchain are working
as expected. For this we are going to perform a simple sanity check:</para>

<screen><userinput>echo 'main(){}' &gt; dummy.c
cc dummy.c
readelf -l a.out | grep ': /lib'</userinput></screen>

<para>If everything is working correctly, there should be no errors, and the
output of the last command will be:</para>

<blockquote><screen>[Requesting program interpreter: /lib/ld-linux.so.2]</screen></blockquote>

<para>(Of course allowing for platform specific differences in dynamic linker
name). Note especially that <filename class="directory">/lib</filename> now
appears as the prefix of our dynamic linker. If you did not receive the output
as shown above, or received no output at all, then something is seriously wrong.
You will need to investigate and retrace your steps to find out where the
problem is and correct it. There is no point in continuing until this is done.
Most likely something went wrong with the specs file amendment above.</para>

<para>Once you are satisfied that all is well, clean up the test files:</para>

<screen><userinput>rm dummy.c a.out</userinput></screen>
</caution>

<!-- HACK - Force some whitespace to appease tidy -->
<literallayout></literallayout>

</sect1>


&c6-binutils;
&c6-gcc;

&c6-coreutils;
&c6-zlib;
&c6-lfs-utils;
&c6-findutils;
&c6-gawk;
&c6-ncurses;
&c6-vim;
&c6-m4;
&c6-bison;
&c6-less;
&c6-groff;
&c6-sed;
&c6-flex;
&c6-gettext;
&c6-nettools;
&c6-inetutils;
&c6-perl;
&c6-texinfo;
&c6-autoconf;
&c6-automake;
&c6-bash;
&c6-file;
&c6-libtool;
&c6-bzip2;
&c6-diffutils;
&c6-ed;
&c6-kbd;
&c6-e2fsprogs;
&c6-grep;
&c6-grub;
&c6-gzip;
&c6-man;
&c6-make;
&c6-modutils;
&c6-patch;
&c6-procinfo;
&c6-procps;
&c6-psmisc;
&c6-shadowpwd;
&c6-sysklogd;
&c6-sysvinit;
&c6-tar;
&c6-utillinux;
&c6-gcc-2953;


<sect1 id="ch-system-revisedchroot">
<title>Revised chroot command</title>
<?dbhtml filename="revisedchroot.html" dir="chapter06"?>

<para>From now on when you exit the chroot environment and wish to re-enter
it, you should run the following modified chroot command:</para>

<screen><userinput>chroot $LFS /usr/bin/env -i \
&nbsp;&nbsp;&nbsp;&nbsp;HOME=/root TERM=$TERM PS1='\u:\w\$ ' \
&nbsp;&nbsp;&nbsp;&nbsp;PATH=/bin:/usr/bin:/sbin:/usr/sbin \
&nbsp;&nbsp;&nbsp;&nbsp;/bin/bash --login</userinput></screen>

<para>The reason being there is no longer any need to use programs from the
<filename class="directory">/tools</filename> directory. However, we don't
want to remove the <filename class="directory">/tools</filename> directory
just yet. There is still some use for it towards the end of the book.</para>

</sect1>


&c6-bootscripts;
&c6-aboutdebug;

</chapter>