Ubuntu 18.04
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Initial Settings : Sudo Settings
2018/04/27
 
Configure Sudo to separate users' duty if some people share privileges.
[1] Install Sudo.
root@dlp:~#
apt install sudo

[2] Grant root privilege to a user all.
root@dlp:~#
# 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@dlp:~$
/sbin/reboot

Failed to set wall message, ignoring: Interactive authentication required.
Failed to reboot system via logind: Interactive authentication required.
Failed to open /dev/initctl: Permission denied
Failed to talk to init daemon.
# denied normally

ubuntu@dlp:~$
sudo /sbin/reboot

[sudo] password for ubuntu:    
# password of [ubuntu]
Session terminated, terminating shell...   # run normally
[3] In addition to the setting of [1], add settings that some commands are not allowed.
root@dlp:~#
# 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@dlp:~$
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
[4] Grant privilege of some commands to users in a group.
root@dlp:~#
# add aliase 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@dlp:~#
groupadd usermgr

root@dlp:~#
vi /etc/group
# add a user in this group

usermgr:x:1002:
ubuntu
# verify with user [ubuntu]

ubuntu@dlp:~$
sudo /usr/sbin/useradd testuser

ubuntu@dlp:~$    
# run normally

ubuntu@dlp:~$
sudo /usr/bin/passwd testuser

Enter new UNIX password:
Retype new UNIX password:
passwd: password updated successfully
[5] Grant privilege of some commands to a user.
root@dlp:~#
# add to the end

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

# verify with user [fedora]

fedora@dlp:~$
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 [cent]

cent@dlp:~$
sudo /usr/sbin/userdel -r testuser

cent@dlp:~$    
# run normally
# verify with user [suse]

suse@dlp:~$
sudo /usr/bin/vim /root/.profile
# run normally

# ~/.profile: executed by Bourne-compatible login shells.
[6] The logs for sudo are kept in '/var/log/auth.log', but there are many kind of logs in it. So if you'd like to keep only sudo's log in another file, Set like follows.
root@dlp:~#
# add to the end

Defaults syslog=local1
root@dlp:~#
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@dlp:~#
systemctl restart rsyslog
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