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<?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-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 maintains 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 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>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 > /etc/hosts << 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 > /etc/passwd << "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 > /etc/passwd << "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 > /etc/group << "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:
usb:x:14:
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 > /etc/group << "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:
usb:x:14:
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—they are groups
decided on in part by the requirements of the Udev configuration in Chapter
9, and in part by common convention 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
<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> for it 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" >> /etc/passwd
echo "tester:x:101:" >> /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>
<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>
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