Listing different information
If you want to list different types of information to check who is logged in to your system, use eo option. Where e show all the processes and o controls the output.
ps -eo pid,user
Look at the above snapshot, it displays process ID and user name as mentioned in the argument.
ps -eo pid,user,ppid,args
Look at the above snapshot, it displays process ID, user name, parent PID and args.