source: chapter07/createfiles.xml

<?xml version="1.0" encoding="UTF-8"?>
<!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-tools-createfiles">
  <?dbhtml filename="createfiles.html"?>

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

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

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

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

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

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

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

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

<screen><userinput>ln -sv /proc/self/mounts /etc/mtab</userinput></screen>

  <para>Create a basic <filename>/etc/hosts</filename> file to be
  referenced in some test suites, and in one of Perl's configuration files
  as well:</para>

<screen><userinput>cat &gt; /etc/hosts &lt;&lt; EOF
<literal>127.0.0.1  localhost $(hostname)
::1        localhost</literal>
EOF</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 revision="sysv"><userinput>cat &gt; /etc/passwd &lt;&lt; "EOF"
<literal>root:x:0:0:root:/root:/bin/bash
bin:x:1:1:bin:/dev/null:/usr/bin/false
daemon:x:6:6:Daemon User:/dev/null:/usr/bin/false
messagebus:x:18:18:D-Bus Message Daemon User:/run/dbus:/usr/bin/false
uuidd:x:80:80:UUID Generation Daemon User:/dev/null:/usr/bin/false
nobody:x:65534:65534:Unprivileged User:/dev/null:/usr/bin/false</literal>
EOF</userinput></screen>

<screen revision="systemd"><userinput>cat &gt; /etc/passwd &lt;&lt; "EOF"
<literal>root:x:0:0:root:/root:/bin/bash
bin:x:1:1:bin:/dev/null:/usr/bin/false
daemon:x:6:6:Daemon User:/dev/null:/usr/bin/false
messagebus:x:18:18:D-Bus Message Daemon User:/run/dbus:/usr/bin/false
systemd-journal-gateway:x:73:73:systemd Journal Gateway:/:/usr/bin/false
systemd-journal-remote:x:74:74:systemd Journal Remote:/:/usr/bin/false
systemd-journal-upload:x:75:75:systemd Journal Upload:/:/usr/bin/false
systemd-network:x:76:76:systemd Network Management:/:/usr/bin/false
systemd-resolve:x:77:77:systemd Resolver:/:/usr/bin/false
systemd-timesync:x:78:78:systemd Time Synchronization:/:/usr/bin/false
systemd-coredump:x:79:79:systemd Core Dumper:/:/usr/bin/false
uuidd:x:80:80:UUID Generation Daemon User:/dev/null:/usr/bin/false
systemd-oom:x:81:81:systemd Out Of Memory Daemon:/:/usr/bin/false
nobody:x:65534:65534:Unprivileged User:/dev/null:/usr/bin/false</literal>
EOF</userinput></screen>

  <para>The actual password for <systemitem class="username">root</systemitem>
  will be set later.</para>

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

<screen revision="sysv"><userinput>cat &gt; /etc/group &lt;&lt; "EOF"
<literal>root:x:0:
bin:x:1:daemon
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:
cdrom:x:15:
adm:x:16:
messagebus:x:18:
input:x:24:
mail:x:34:
kvm:x:61:
uuidd:x:80:
wheel:x:97:
users:x:999:
nogroup:x:65534:</literal>
EOF</userinput></screen>

<screen revision="systemd"><userinput>cat &gt; /etc/group &lt;&lt; "EOF"
<literal>root:x:0:
bin:x:1:daemon
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:
cdrom:x:15:
adm:x:16:
messagebus:x:18:
systemd-journal:x:23:
input:x:24:
mail:x:34:
kvm:x:61:
systemd-journal-gateway:x:73:
systemd-journal-remote:x:74:
systemd-journal-upload:x:75:
systemd-network:x:76:
systemd-resolve:x:77:
systemd-timesync:x:78:
systemd-coredump:x:79:
uuidd:x:80:
systemd-oom:x:81:
wheel:x:97:
users:x:999:
nogroup:x:65534:</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 Chapter
  9, and in part by common conventions employed by a number of existing Linux
  distributions. In addition, some test suites rely on specific users or
  groups.  The Linux Standard Base (LSB, available at <ulink
  url="https://refspecs.linuxfoundation.org/lsb.shtml"/>) only recommends 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. The GID of 5 is widely used for the
  <systemitem class="groupname">tty</systemitem> group, and the number 5 is
  also used in <phrase revision="systemd">systemd</phrase>
  <phrase revision="sysv"><filename>/etc/fstab</filename></phrase> for the
  <systemitem class="filesystem">devpts</systemitem> filesystem.
  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>The ID 65534 is used by the kernel for NFS and separate user
  namespaces for unmapped users and groups (those exist on the NFS server
  or the parent user namespace, but <quote>do not exist</quote> on the local
  machine or in the separate namespace).  We assign
  <systemitem class="username">nobody</systemitem> and
  <systemitem class="groupname">nogroup</systemitem> to avoid an
  unnamed ID.  But other distros may treat this ID differently, so any
  portable program should not depend on this assignment.</para>

  <para>Some tests in <xref linkend="chapter-building-system"/> need a regular
  user. We add this user here and delete this account at the end of that
  chapter.</para>

<screen><userinput>echo "tester:x:101:101::/home/tester:/bin/bash" &gt;&gt; /etc/passwd
echo "tester:x:101:" &gt;&gt; /etc/group
install -o tester -d /home/tester</userinput></screen>

  <para>To remove the <quote>I have no name!</quote> prompt, start a new
  shell. Since 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 /usr/bin/bash --login</userinput></screen>

  <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,faillog,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/faillog</filename> file records
  failed login attempts.  The <filename>/var/log/btmp</filename> file records
  the bad login attempts.</para>

  <!-- systemd no longer creates this -->
  <note revision='sysv'><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>

  <!-- AFAIK they are not vital for system function, users requiring such
       info should rely on systemd-logind or elogind or some custom PAM
       module.  Maybe we can stop to create them at all.  -->
  <note>
    <para>
      The <phrase revision='sysv'><filename>utmp</filename>,
      </phrase><filename>wtmp</filename>, <filename>btmp</filename>, and
      <filename>lastlog</filename> files use 32-bit integers for timestamps
      and they'll be fundamentally broken after year 2038.  Many packages
      have stopped using them and other packages are going to stop using
      them.  It is probably best to consider them deprecated.
    </para>
  </note>

</sect1>