Historically, Linux maintained a list of the mounted file systems in
the file /etc/mtab
. Modern kernels
maintain this list internally and expose it to the user via the
/proc
filesystem. To satisfy utilities
that expect to find /etc/mtab
, create
the following symbolic link:
ln -sv /proc/self/mounts /etc/mtab
Create a basic /etc/hosts
file to be
referenced in some test suites, and in one of Perl's configuration
files as well:
cat > /etc/hosts << EOF
127.0.0.1 localhost $(hostname)
::1 localhost
EOF
In order for user root
to be able to
login and for the name “root” to be recognized, there must be
relevant entries in the /etc/passwd
and
/etc/group
files.
Create the /etc/passwd
file by running
the following command:
cat > /etc/passwd << "EOF"
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
EOF
The actual password for root
will be
set later.
Create the /etc/group
file by running
the following command:
cat > /etc/group << "EOF"
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:
EOF
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 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
https://refspecs.linuxfoundation.org/lsb.shtml)
only recommends that, besides the group root
with a Group ID (GID) of 0, a group
bin
with a GID of 1 be present. The
GID of 5 is widely used for the tty
group, and the number 5 is also used in systemd for the devpts
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.
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 “do not exist”
on the local machine or in the separate namespace). We assign
nobody
and nogroup
to avoid an unnamed ID. But other distros
may treat this ID differently, so any portable program should not
depend on this assignment.
Some tests in Chapter 8 need a regular user. We add this user here and delete this account at the end of that chapter.
echo "tester:x:101:101::/home/tester:/bin/bash" >> /etc/passwd echo "tester:x:101:" >> /etc/group install -o tester -d /home/tester
To remove the “I have
no name!” prompt, start a new shell. Since the
/etc/passwd
and /etc/group
files have been created, user name and
group name resolution will now work:
exec /usr/bin/bash --login
The login, agetty, and init 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:
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
The /var/log/wtmp
file records all
logins and logouts. The /var/log/lastlog
file records when each user last
logged in. The /var/log/faillog
file
records failed login attempts. The /var/log/btmp
file records the bad login attempts.
The /run/utmp
file records the users
that are currently logged in. This file is created dynamically in
the boot scripts.