lfs-book/chapter06/createfiles.xml

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<!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
sed 's/tools/usr/' /tools/lib/libstdc++.la > /usr/lib/libstdc++.la
ln -sv bash /bin/sh</userinput></screen>

  <para>Historically, Linux maintains a list of the mounted file systems in the
  file <filename>/etc/mtab</filename>. Modern kernels maintain this list
  internally and exposes it to the user via the <filename
  class="directory">/proc</filename> filesystem. To satisfy utilities that
  expect the presence of <filename>/etc/mtab</filename>, create the following
  symbolic link:</para>

<screen><userinput>ln -sv /proc/self/mounts /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
bin:x:1:1:bin:/dev/null:/bin/false
daemon:x:6:6:daemon:/dev/null:/bin/false
messagebus:x:18:18:D-Bus Message Daemon User:/var/run/dbus:/bin/false
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:
tape:x:4:
tty:x:5:
daemon:x:6:
floppy:x:7:
disk:x:8:
lp:x:9:
dialout:x:10:
audio:x:11:
video:x:12:
utmp:x:13:
usb:x:14:
cdrom:x:15:
adm:x:16:
messagebus:x:18:
systemd-journal:x:23:
mail:x:34:
nogroup:x:99:
users:x:100:</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/log/{btmp,lastlog,wtmp}
chgrp -v utmp /var/log/lastlog
chmod -v 664  /var/log/lastlog
chmod -v 600  /var/log/btmp</userinput></screen>

  <para>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>

  <note><para>The <filename>/run/utmp</filename> file records the users that
  are currently logged in.  This file is created dynamically in the boot
  scripts.</para></note>

</sect1>