The ps command can be used to view a static snapshot of active processes. The top command can be used to view processes in real time. The ps command without any options will display only the processes being used by the current user in the current shell.

[john.doe@server1 ]# ps
 PID  TTY        TIME  CMD
4012  pts/2  00:00:00  bash
4657  pts/2  00:00:00  ps

• The -A or -e options can be used to display all processes running on the system
• The -p option can be used to display a process associated with a certain process ID number (PID)
• The -U option can be used to display processes invoked by a certain user
• The -C option can be used to display processes invoked by a system service
• The -f or -F options can be used to add additional columns to the output
• The -o etime option can be used to determine how long a processes has been running for

grep

Often, the grep is used with the ps command.

[john.doe@server1 ]# ps | grep foo

This will always show that the grep command itself has a PID.

john.doe  29124  23915  0  03:02  pts/0  00:00:00 grep --color=auto foo

If you want to remove grep from the output, do this.

[john.doe@server1 ]# ps | grep foo | grep -v grep