Processes

Command	Effect
ps aux	All processes with CPU, memory and command line.
ps -ef --forest	All processes as a tree of parents and children.
pgrep -a nginx	PIDs and command lines of processes matching a name.
htop	Interactive viewer; F6 sorts, F9 sends a signal.
kill <pid>	Asks a process to terminate (SIGTERM).
kill -9 <pid>	Kills it immediately (SIGKILL).
pkill nginx	Sends SIGTERM to all processes matching a name.
nice -n 10 cmd	Starts a command with lower priority.
renice -n 10 -p <pid>	Lowers the priority of a running process.

Signals

Signal	Number	Default effect
SIGHUP	1	Terminate. Many daemons reload their configuration instead.
SIGINT	2	Terminate; sent by Ctrl+C.
SIGKILL	9	Terminate immediately. Can’t be caught, so no cleanup happens.
SIGTERM	15	Terminate cleanly. The default of kill.
SIGSTOP	19	Pause; Ctrl+Z sends the similar SIGTSTP.
SIGCONT	18	Continue a paused process.

Tip

Try SIGTERM first and wait a few seconds. SIGKILL gives the process no chance to save data or remove lock files.

Jobs in the shell

stateDiagram-v2
  direction LR
  Foreground --> Stopped: Ctrl+Z
  Stopped --> Background: bg
  Stopped --> Foreground: fg
  Background --> Foreground: fg
  [*] --> Background: cmd &

Command	Effect
cmd &	Starts a command in the background.
jobs	Lists the jobs of the current shell.
bg %1	Continues job 1 in the background.
fg %1	Brings job 1 to the foreground.
disown %1	Detaches a job so it keeps running when the shell is closed.
nohup cmd &	Starts a command that ignores the hangup when you log out.