Linux sudo

Sudo - grant a user root privilages

sudo usermod -aG sudo nameofuser  #enough for Ubuntu, logout required
sudo passwd root #sets root password, so it can be used to login

Edit safely /etc/sudoers file

sudo visudo

User rules fields explained

        The first ALL is the users allowed
         |    The second one is the hosts; on all hosts (if you distribute the same sudoers file to many computers)
         |     |
   piotr ALL=(ALL:ALL) ALL
                  /     |
                 /   The last one is the commands allowed
         The third one is the user as you are running the command

In examples below names beginning with a "%" indicate group names in /etc/group

root  ALL=(ALL)    ALL              #standard root entry
piotr ALL=(ALL)    NOPASSWD: ALL    #user can run as root without password

piotr ALL=         NOPASSWD: ALL      #piotr will not be prompted for password, just another format to above
piotr ALL= NOPASSWD: /usr/bin/service #piotr will not be prompt for password while running 'service' command
%wheel ALL=(ALL)   NOPASSWD: ALL      #members of 'wheel' group can run without a password

If you find a number of entries applied to your user, the last entry takes precedence

sudo -l #list all of the rules in the /etc/sudoers that apply to your user
sudo -k #clear the timer

Add user to the elevated privileges group

In Ubuntu adding a user to admin group will grant root user level access. Adding the user to sudo group will allow to execute any command as root user.

sudo usermod -aG nameofgroup nameofuser

In RedHat/CentOS add an user to a group wheel to enable sudo commands execution as root user.

sudo usermod -aG wheel nameofuser

In both examples above you need to login again for changes to be applied.