The su command is used to switch to another user, in other words, change user ID during a normal login session (that is why it is sometimes referred to as switch
(-)user by a number of Linux users). If executed without a username, for example,
su -it will log in as root user by default.
Following command, then you will be prompted for the password of the user you’re switching to.
$ su ucartz
When you invoke
su with a
--login flags, it offers you a login interface similar to when you are logging on normally. All the commands below are equivalent to each other.
$ su - ucartz OR $ su -l ucartz OR $ su --login ucartz
When you run
su without a username, you will automatically become the superuser. You will be given root’s default environment, including the path to executable files changes. You will also land into root’s home directory: