“root” super user is the king of the users in Linux/Unix. Having root access grant full and unlimited access to the Linux box. I will show how to allow root access to a user in a Linux system. Typically root level access used in system administration. It’s always a pain to give others (users) root access. You need to be careful and withdraw the access once need is finished.
According to Linux file system permissions root or super user has full permission read(r), write 
and execute(x) to any file. By default root user id is 0.
I am going to crate two users namely user1 and user2. Then I will give root access to user1 .
Method : 1 Using Usermod Command
[root@mypc Desktop]# adduser user1
[root@mypc Desktop]# adduser user2
[root@mypc Desktop]# groupadd test
These are the groups I have in my Linux box
[root@mypc /]# groups
root bin daemon sys adm disk wheel
I am going to add user1 to root group
[root@mypc Desktop]# usermod -G root user1
Below command provide existing user the root privilege
[root@mypc Desktop]# usermod -g 0 -o root_user
Method 2 : Using Useradd Command
I have add new user user3 to root group using one single command
[root@mypc /]# useradd -m -G root user3
[root@mypc /]# groups user3
user3 : user3 root
Another option using useradd command
Useradd -c “Imitation Root” -d /home/root_user -m -k /etc/skel -s /bin/bash -u 0 -o -g root root_user
Method 3 : Editing /etc/passwd file
Edit /etc/passwd for the particular user. Change that user’s UID and GID to 0 then the user will have the permissions of root.
root:x:0:0:root:/root:/bin/bash
temproot:x:128:128:temproot
Now temproot user should have root privilege
root:x:0:0:root:/root:/bin/bash
temproot:x:0:0:temproot
Method 4 : Setting as Sudo User
The sudo configuration file is /etc/sudoers and you can edit this file using visudo command: # visudo. Using visudo protects from conflicts and guarantees that the right syntax is used.
Full Access to Specific Users
Add below entry in the file
bob, tom ALL=(ALL) ALL
This method is not a good idea because this allows bob and tom to use the su command to grant themselves permanent root privileges thereby skipping the command logging features of sudo.
Grant access to specific user to specific files
This entry allows bob and all the members of the group operator to gain access to all the program files in the /sbin and /usr/sbin directories, plus the privilege of running the command /usr/oracle/backup.pl.
bob, %operator ALL= /sbin/, /usr/sbin, /usr/oracle/backup.pl
Network and CyberSecurity Professional 