Normally in the Unix/Linux operation system, there is a superuser root which is equivalent to Administrator in Windows operating system. This powerful user privilege give the maximum privilege to the access user. That mean any user with this root privilege can do anything and everything. If we try to do our daily works as the superuser it lets to dangerous to the system.

There for by default, the root account password is locked in Ubuntu. This means you cannot login as root directly or use the su command to become the root user. Well, its an advantage to avoid unnecessarily system crashes. But the root account is physically exists in its user groups. So we can run programs with root-level privileges. This is where sudo comes in - it authorized to run command with root-level privilege. Simplify, open the Terminal in the Unix environment and use sudo for commands that require root privileges.

Note : Enabling the root account is rarely necessary. Almost everything you need to do as administrator of an Ubuntu system can be done via sudo.

root account
Enabling the root account.
sudo -i

To enable the root account (i.e. set a password) use:
sudo passwd root

Re-disabling your root account
sudo usermod -p '!' root