How to configure passwordless sudo in Linux

sudo allows a regular user to run commands that require administrative privilege. It works by running any commands via sudo instead of direct execution. A user is then required to authenticate to the system before the command executes.

sudo could be configured so that a select user or group members do not need to enter their password to authenticate when running their commands via sudo. This could be done by configuring the sudoers file using the visudo tool at the terminal.

1. Launch your favorite terminal application.
2. Display current sudo privilege for your user.

   user@host:~$ sudo -l
   Matching Defaults entries for user on host:
       env_reset, mail_badpass,
       secure_path=/usr/local/sbin\:/usr/local/bin\:/usr/sbin\:/usr/bin\:/sbin\:/bin\:/snap/bin
   
   User user may run the following commands on host:
       (ALL : ALL) ALL

3. Open sudoers file using visudo.

   $ sudo visudo

4. Add ALL = (ALL) NOPASSWD: ALL line to your username (or for any other user) so your user could run all commands without password.

   user       ALL = (ALL) NOPASSWD: ALL

   Passwordless sudo could be assigned to a group by replacing the username with %groupname or by replacing it with ALL to allow passwordless sudo for all users in the system.

5. Exit visudo by saving the file.
6. Check sudo privilege for your user again to confirm changes are successful.

   user@host:~$ sudo -l
   Matching Defaults entries for user on host:
       env_reset, mail_badpass,
       secure_path=/usr/local/sbin\:/usr/local/bin\:/usr/sbin\:/usr/bin\:/sbin\:/bin\:/snap/bin
   
   User user may run the following commands on host:
       (ALL : ALL) ALL
       (ALL) NOPASSWD: ALL

7. Try running commands using sudo with no password.

   user@host:~$ sudo ls -la /root
   total 32
   drwx------  5 root root 4096 Jul 24 05:54 .
   drwxr-xr-x 19 root root 4096 Jul 24 05:53 ..
   -rw-------  1 root root   18 Jul 19 01:57 .bash_history
   -rw-r--r--  1 root root 3106 Aug  6  2018 .bashrc
   drwxr-xr-x  3 root root 4096 Jul 24 05:54 .local
   -rw-r--r--  1 root root  148 Aug  6  2018 .profile
   drwxr-xr-x  3 root root 4096 Apr 22 07:56 snap
   drwx------  2 root root 4096 Apr 22 07:56 .ssh