Question

I am giving the following command on Shell Prompt :
$ps -u 0

I am unable to understand what is the output of the same. Can anyone please elaborate on the same?

Answer 1

Copied from man ps:

   -u userlist     Select by effective user ID (EUID) or name.
                   This selects the processes whose effective user name or ID is in userlist. The
                   effective user ID describes the user whose file access permissions are used by the
                   process (see geteuid(2)). Identical to U and --user.

Meaning:
it prints all the processes started with user 0 (root)
See man ps for more informations

Edit:
To see all running processes, not just from one user, you can use “ps ax”