id prints information about the given user
id picklu //print information about user(including uid, gid, groups, etc)
whoami //prints the user name associated with the current effective user ID.
groups //prints the names of the primary and any supplementary groups for each
fingers //displays information about the system users
who //show who is logged on
who -a show all users log on to the system in different terminal.
su allows one user to temporarily become another user
su become root user
su - become root user with all the all the environment
su - change to supplied user