Ubuntu 22.04 LTS: Manage Sudo

Initial Settings

This section explain how to install and configure Sudo to separate users' duty if some people share privileges.

Step [1] Install Sudo.

root@bizantum:~# apt -y install sudo

Step [2] Grant root privilege to a user all.

root@bizantum:~# visudo
# add to the end: user [ubuntu] can use all root privilege
ubuntu    ALL=(ALL:ALL) ALL

# how to write ⇒ [user] [host=(owner)] [command]
# push [Ctrl + x] key to quit visudo
# verify with user [ubuntu]
ubuntu@bizantum:~$ /sbin/reboot
Failed to set wall message, ignoring: Interactive authentication required.
Failed to reboot system via logind: Interactive authentication required.
Failed to open initctl fifo: Permission denied
Failed to talk to init daemon.
# denied normally
ubuntu@bizantum:~$ sudo /sbin/reboot
[sudo] password for ubuntu:                # password of [ubuntu]

Session terminated, terminating shell...   # run normally

Step [3] In addition to the setting of ^{Step [2]}, add settings that some commands are not allowed.

root@bizantum:~# visudo
# add alias for the kind of shutdown commands
# Cmnd alias specification

Cmnd_Alias SHUTDOWN = /sbin/halt, /sbin/shutdown, \
/sbin/poweroff, /sbin/reboot, /sbin/init, /bin/systemctl 

# add (commands in alias [SHUTDOWN] are not allowed)
ubuntu    ALL=(ALL:ALL) ALL, !SHUTDOWN

# verify with user [ubuntu]
ubuntu@bizantum:~$ sudo /sbin/shutdown -r now
[sudo] password for ubuntu:

Sorry, user ubuntu is not allowed to execute '/sbin/shutdown -r now' as root on ubuntu.
# denied normally

Step [4] Grant privilege of some commands to users in a group.

root@bizantum:~# visudo
# add alias for the kind of user management comamnds
# Cmnd alias specification
Cmnd_Alias USERMGR = /usr/sbin/adduser, /usr/sbin/useradd, /usr/sbin/newusers, \
/usr/sbin/deluser, /usr/sbin/userdel, /usr/sbin/usermod, /usr/bin/passwd 

# add to the end
%usermgr ALL=(ALL) USERMGR
root@bizantum:~# groupadd usermgr
root@bizantum:~# vi /etc/group
# add a user in this group
usermgr:x:1002:ubuntu
# verify with user [ubuntu]
ubuntu@bizantum:~$ sudo /usr/sbin/useradd testuser
ubuntu@bizantum:~$     # run normally
ubuntu@bizantum:~$ sudo /usr/bin/passwd testuser
Enter new UNIX password:
Retype new UNIX password:
passwd: password updated successfully

Step [5] Grant privilege of some commands to a user.

root@bizantum:~# visudo
# add to the end for each user setting
fedora    ALL=(ALL:ALL) /usr/sbin/visudo
centos    ALL=(ALL:ALL) /usr/sbin/adduser, /usr/sbin/useradd, /usr/sbin/newusers, \
                        /usr/sbin/deluser, /usr/sbin/userdel, /usr/sbin/usermod, /usr/bin/passwd
debian    ALL=(ALL:ALL) /usr/bin/vim

# verify with user [fedora]
fedora@bizantum:~$ sudo /usr/sbin/visudo
# run normally
## Sudoers allows particular users to run various commands as
## the root user, without needing the root password.
# verify with user [centos]
centos@bizantum:~$ sudo /usr/sbin/userdel -r testuser
centos@bizantum:~$     # run normally
# verify with user [debian]
debian@bizantum:~$ sudo /usr/bin/vim /root/.profile
# run normally
# ~/.profile: executed by Bourne-compatible login shells.

Step [6] It's possible to display Sudo logs on Journald ( with [journalctl] command ) or Rsyslogd ( in [/var/log/auth.log] file ), however, if you'd like to keep only Sudo logs in another file, Configure like follows.

root@bizantum:~# visudo
# add to the end
Defaults syslog=local1
root@bizantum:~# vi /etc/rsyslog.d/50-default.conf
# line 8 : add
local1.*                        /var/log/sudo.log
auth,authpriv.*;local1.none     /var/log/auth.log
*.*;auth,authpriv.none          -/var/log/syslog

root@bizantum:~# systemctl restart rsyslog