CentOS Stream 9: Sudo Settings

Initial Settings

Configure Sudo to separate users' duty if some people share privileges. It does not need to install sudo manually because it is installed by default even if Minimal installed environment.

Step [1] Transfer root privilege all to a user.

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

# how to write ⇒ destination host=(owner) command
# verify with user [cent]
[cent@bizantum ~]$ /usr/bin/cat /etc/shadow
/usr/bin/cat: /etc/shadow: Permission denied   # denied normally
[cent@bizantum ~]$ sudo /usr/bin/cat /etc/shadow
Password:     # user's own password

.....
.....
systemd-oom:!*:18957::::::
systemd-resolve:!*:18957::::::     # just executed

Step [2] In addition to the setting of ^{Step [1]}, set some commands prohibit.

[root@bizantum ~]# visudo
# line 25 : add
# for example, set alias for the kind of shutdown commands
Cmnd_Alias SHUTDOWN = /usr/sbin/halt, /usr/sbin/shutdown, \
/usr/sbin/poweroff, /usr/sbin/reboot, /usr/sbin/init, /usr/bin/systemctl

# add ( prohibit commands in alias [SHUTDOWN] )
cent  ALL=(ALL)       ALL, !SHUTDOWN

# verify with user [cent]
[cent@bizantum ~]$ sudo /usr/sbin/reboot
[sudo] password for cent:
Sorry, user cent is not allowed to execute '/usr/sbin/reboot' as root on bizantum.local.   # denied normally

Step [3] Transfer some commands with root privilege to users in a group.

[root@bizantum ~]# visudo
# line 25 : add
# for example, set alias for the kind of user management commands
Cmnd_Alias USERMGR = /usr/sbin/useradd, /usr/sbin/userdel, /usr/sbin/usermod, \
/usr/bin/passwd

# add to the end
%usermgr ALL=(ALL) USERMGR

[root@bizantum ~]# groupadd usermgr
[root@bizantum ~]# usermod -aG usermgr redhat
# verify with user [redhat]
[redhat@bizantum ~]$ sudo /usr/sbin/useradd testuser
[redhat@bizantum ~]$ sudo /usr/bin/passwd testuser
Changing password for user testuser.
New UNIX password:
Retype new UNIX password:
passwd: all authentication tokens updated successfully.   # just executed

Step [4] Transfer a command with root privilege to a user

[root@bizantum ~]# visudo
# add to the end : settings for each user
fedora  ALL=(ALL)       /usr/sbin/visudo
ubuntu  ALL=(ALL)       /usr/sbin/useradd, /usr/sbin/userdel, /usr/sbin/usermod, /usr/bin/passwd
debian  ALL=(ALL)       /usr/bin/vi

# for example, verify with user [fedora]
[fedora@bizantum ~]$ sudo /usr/sbin/visudo
## Sudoers allows particular users to run various commands as
## the root user, without needing the root password.
##   # just executed

Step [5] It's possible to display Sudo logs on Journald ( with [journalctl] command ) or Rsyslogd ( in [/var/log/secure] file ), however, if you'd like to keep only Sudo logs in another file, Configure like follows.

[root@bizantum ~]# visudo
# add to the end
# for example, output logs to [local1] facility
Defaults syslog=local1
[root@bizantum ~]# vi /etc/rsyslog.conf
# line 46,47 : add like follows
*.info;mail.none;authpriv.none;cron.none;local1.none    /var/log/messages
local1.*                                                /var/log/sudo.log

# The authpriv file has restricted access.
authpriv.*                                              /var/log/secure

[root@bizantum ~]# systemctl restart rsyslog