Initial Settings : Configure Sudo2023/06/14

	Configure Sudo to separate users' duty if some people share privileges.
[1]	Install Sudo.

root@localhost:~#

apt -y install sudo

[2]	Transfer root privilege to a user all.

root@localhost:~#

visudo

# add to the end : user [bookworm] can use all root privilege
# how to write ⇒ destination host=(owner) command

bookworm    ALL=(ALL:ALL) ALL

# push [Ctrl + x] key to quit visudo

# verify with user [bookworm]

bookworm@localhost:~$

cat /etc/shadow

cat: /etc/shadow: Permission denied
# denied

bookworm@localhost:~$

sudo cat /etc/shadow

[sudo] password for bookworm:   # bookworm's password
root:xxxxxxxxxx:19520:0:99999:7:::
daemon:*:19520:0:99999:7:::
bin:*:19520:0:99999:7:::
sys:*:19520:0:99999:7:::
sync:*:19520:0:99999:7:::
.....
.....
# possible executed

[3]	In addition to the setting [1], set that some commands are not allowed.

root@localhost:~#

visudo

# add alias for the kind of shutdown commands

# Cmnd alias specification

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

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

# verify with user [bookworm]

bookworm@localhost:~$

sudo /usr/sbin/reboot

[sudo] password for bookworm:
Sorry, user bookworm is not allowed to execute '/usr/sbin/reboot' as root on localhost.

# denied as setting

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

root@localhost:~#

visudo

# add alias for the kind of user management commands

# 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:ALL) USERMGR

root@localhost:~#

groupadd usermgr

root@localhost:~#

usermod -aG usermgr bookworm

# verify with user [bookworm]

bookworm@localhost:~$

sudo /usr/sbin/useradd testuser

bookworm@localhost:~$
bookworm@localhost:~$

sudo /usr/bin/passwd testuser

Enter new UNIX password:
Retype new UNIX password:
passwd: password updated successfully

# possible execute

[5]	Transfer some specific commands with root privilege to a user.

root@localhost:~#

visudo

# add to the end : set specific commands to each user

fedora   ALL=(ALL:ALL) /usr/sbin/visudo
debian   ALL=(ALL:ALL) /usr/sbin/adduser, /usr/sbin/useradd, /usr/sbin/newusers, \
                       /usr/sbin/deluser, /usr/sbin/userdel, /usr/sbin/usermod, /usr/bin/passwd
ubuntu   ALL=(ALL:ALL) /usr/bin/vim

# verify with user [fedora]

fedora@localhost:~$

sudo /usr/sbin/visudo

# possible open and edit

## Sudoers allows particular users to run various commands as
## the root user, without needing the root password.
##

# verify with user [debian]

debian@localhost:~$

sudo /usr/sbin/userdel -r testuser

debian@localhost:~$

# possible execute

# verify with user [ubuntu]

ubuntu@localhost:~$

sudo /usr/bin/vim /root/.profile

# possible open and edit

# ~/.profile: executed by Bourne-compatible login shells.

[6]	It's possible to display Sudo logs on Journald like follows.

root@localhost:~#

journalctl -t sudo

Jun 14 00:03:05 debian sudo[1656]: bookworm : TTY=ttyS0 ; PWD=/home/bookworm ; USER=root ; COMMAND=/usr/bin/cat /etc/shadow
Jun 14 00:03:05 debian sudo[1656]: pam_unix(sudo:session): session opened for user root(uid=0) by root(uid=1001)
Jun 14 00:03:05 debian sudo[1656]: pam_unix(sudo:session): session closed for user root
Jun 14 00:09:41 debian sudo[1687]: bookworm : TTY=ttyS0 ; PWD=/home/bookworm ; USER=root ; COMMAND=/usr/bin/ls -l /root
Jun 14 00:09:41 debian sudo[1687]: pam_unix(sudo:session): session opened for user root(uid=0) by root(uid=1001)
Jun 14 00:09:41 debian sudo[1687]: pam_unix(sudo:session): session closed for user root

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