ps

TLDR

List all processes

$ ps aux

List processes for current user

$ ps -u [username]

Show process tree

$ ps -ef --forest

Show specific process

$ ps -p [pid]

Custom output format

$ ps -eo pid,ppid,cmd,%mem,%cpu

List threads

$ ps -eLf

ps [options]

ps reports process status. Shows running processes.
The tool displays system processes. Essential system utility.
ps lists processes.

All users.

User-oriented format.

Include processes without tty.

-e

Every process.

-f

Full format.

-p PID

Select by PID.

-u USER

Select by user.

--forest

Process tree.

-o FORMAT

Custom output.

BSD and POSIX options differ. Use aux or -ef.

ps is a classic Unix process monitoring utility.