The help pages state …
su – run a shell with substitute user and group id’s
sudo – execute a command as another user (or root)
When ‘sudo‘ is used with a command, the command gets executed with privileges set for the user and the group she belongs to. If a password is required and if it is given initially, the session will be valid depending on the time set for each session and the user needn’t have to type the password within that duration. /etc/sudoers is the location where permission settings for sudoers are being set.
Login as the root and check /etc/sudoers to know what the privilege settings are.
In Ubuntu, by default ‘sudo’ exists for gaining root access and not ‘su’.
So, what is the difference between “su” and “sudo”?
When ‘sudo’ commands is typed, the user is prompted for a password. The password that you enter here is YOUR password. Reason for this is the consideration that a user may leave a system unattended when another may use the same system to gain root access.
When ‘su’ command is typed the password that is asked is the password of the root user account if you want to switch to root user account or the password of the user to whose account you want to switch to.
‘sudo’ command is stored the log entries in /var/log/auth.log enabling users to unwind the tasks previously entered. To perform a task users can be grouped and those users can be given access to perform that specified activity instead of sharing root user password for that activity.
For further read …
https://help.ubuntu.com/community/RootSudo
