There are two option to take on the identity of another user:

• su - start the shell as another user or issue a single command as that user
• sudo - allows a user to execute commands as a different user (usually the root). Config file etc/sudoers defines specific commands that particular users can execute under an assumed identity

Start shell as a root:

victor@rasp-4:~ $ su -
Password:
 
root@rasp-4:~#
root@rasp-4:~# su -l victor
 
victor@rasp-4:~ $

The difference from su:

• The user might be restricted to one or more commands
• sudo does not require an access to superuser's password
• sudo doesn't start a new shell

Running any command as root without having to enter a password:

• sudo visudo - modifies /etc/sudoers/
• Add file to /etc/sudoers.d

Example config for user victor (/etc/sudoers.d/010-victor-nopasswd):

victor ALL=(ALL) NOPASSWD: ALL

Which means:

• ALL=(ALL) - victor can run commands for any user on any machine
• NOPASSWD: ALL - no password needed for any command

Adding a user to the group:

# usermod -aG sudo victor # 'a' - append; 'G' - group