lfs-book/chapter06/createfiles.xml

<?xml version="1.0" encoding="ISO-8859-1"?>
<!DOCTYPE sect1 PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
  "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [
  <!ENTITY % general-entities SYSTEM "../general.ent">
  %general-entities;
]>

<sect1 id="ch-system-createfiles">
  <?dbhtml filename="createfiles.html"?>

  <title>Creating Essential Files and Symlinks</title>

  <indexterm zone="ch-system-createfiles">
    <primary sortas="e-/etc/passwd">/etc/passwd</primary>
  </indexterm>

  <indexterm zone="ch-system-createfiles">
    <primary sortas="e-/etc/group">/etc/group</primary>
  </indexterm>

  <indexterm zone="ch-system-createfiles">
    <primary sortas="e-/var/run/utmp">/var/run/utmp</primary>
  </indexterm>

  <indexterm zone="ch-system-createfiles">
    <primary sortas="e-/var/log/btmp">/var/log/btmp</primary>
  </indexterm>

  <indexterm zone="ch-system-createfiles">
    <primary sortas="e-/var/log/lastlog">/var/log/lastlog</primary>
  </indexterm>

  <indexterm zone="ch-system-createfiles">
    <primary sortas="e-/var/log/wtmp">/var/log/wtmp</primary>
  </indexterm>

  <para>Some programs use hard-wired paths to programs which do not exist yet. In
  order to satisfy these programs, create a number of symbolic links which will be
  replaced by real files throughout the course of this chapter after the software
  has been installed:</para>

<screen><userinput>ln -sv /tools/bin/{bash,cat,echo,pwd,stty} /bin
ln -sv /tools/bin/perl /usr/bin
ln -sv /tools/lib/libgcc_s.so{,.1} /usr/lib
ln -sv /tools/lib/libstdc++.so{,.6} /usr/lib
ln -sv bash /bin/sh</userinput></screen>

  <para>A proper Linux system maintains a list of the mounted file systems in
  the file <filename>/etc/mtab</filename>.  Normally, this file would be
  created when we mount a new file system. Since we will not be mounting any
  file systems inside our chroot environment, create an empty file for
  utilities that expect the presence of <filename>/etc/mtab</filename>:</para>

<screen><userinput>touch /etc/mtab</userinput></screen>

  <para>In order for user <systemitem class="username">root</systemitem> to be
  able to login and for the name <quote>root</quote> to be recognized, there
  must 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"
<literal>root:x:0:0:root:/root:/bin/bash
nobody:x:99:99:Unprivileged User:/dev/null:/bin/false</literal>
EOF</userinput></screen>

  <para>The actual password for <systemitem class="username">root</systemitem>
  (the <quote>x</quote> used 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"
<literal>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:
uucp:x:10:
audio:x:11:
video:x:12:
utmp:x:13:
usb:x:14:
cdrom:x:15:
mail:x:34:
nogroup:x:99:</literal>
EOF</userinput></screen>

  <para>The created groups are not part of any standard&mdash;they are groups
  decided on in part by the requirements of the Udev configuration in this
  chapter, and in part by common convention employed by a number of existing
  Linux distributions. The Linux Standard Base (LSB, available at <ulink
  url="http://www.linuxbase.org"/>) recommends only that, besides the group
  <systemitem class="groupname">root</systemitem> with a Group ID (GID) of 0,
  a group <systemitem class="groupname">bin</systemitem> with a GID of 1 be
  present. All other group names and GIDs can be chosen freely by the system
  administrator since well-written programs do not depend on GID numbers, but
  rather use the group's name.</para>

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

<screen role="nodump"><userinput>exec /tools/bin/bash --login +h</userinput></screen>

  <para>Note the use of the <parameter>+h</parameter> 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. To ensure the use of the newly compiled binaries as soon as they are
  installed, the <parameter>+h</parameter> directive will be used for the duration
  of this chapter.</para>

  <para>The <command>login</command>, <command>agetty</command>, and
  <command>init</command> programs (and others) use a number of log
  files to record information such as who was logged into the system and
  when. However, these programs will not write to the log files if they
  do not already exist. Initialize the log files and give them
  proper permissions:</para>

<screen><userinput>touch /var/run/utmp /var/log/{btmp,lastlog,wtmp}
chgrp -v utmp /var/run/utmp /var/log/lastlog
chmod -v 664 /var/run/utmp /var/log/lastlog</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 when
  each user last logged in. The <filename>/var/log/btmp</filename> file
  records the bad login attempts.</para>

</sect1>