su command and sudo command in linux

su – Substitute User

If one user needs to login as another user in the same CLI(shell)

eg: su -l user-name


Note:

1. Root user can login as any of the other user without needing the password of the other users
2. Normal user can login as any of the other user with password

In some cases where a normal user wants to execute a command(that can normally executed only by root) if the local system administrator(root) is not available, sharing the root’s password is not recommended, so sudo command can be used

sudo

To exec any command with root privilege – prepend sudo in front of the command

eg:sudo useradd testuser

but, not all users are sudo users by default.

To Make a user as a Sudo User in RHEL

Add a user to wheel group
usermod -aG wheel testuser

Now testuser can exec any command with root privilege without needing root password

and all the commands executed by a sudo user will be logged in a file /var/log/secure

if non-sudo user tries to give command it will be reported as a mail(auto-generated) to root