On linux, kill a process is simple, but sometimes, when something goes wrong, a process could fork hundreds and thousands child processes, you can either create a script to kill them all, or find some quick ways to kill them all in one command.

Here is the ways I use, some of them may not work on all linux distributions.

1.kill a group of processes with negative PID(Process ID)

kill  -TERM -PID

Is to kill PID and all its child processes.

2. kill a group of processes with their PGID(Process Group ID)

kill -- -$PGID   Kill using the default signal (TERM = 15)
kill -9 -$PGID   Kill using the KILL signal (9)

3. kill a group processes with only PID info

kill -- -$(ps -o pgid= $PID | grep -o [0-9]*)

Actually, you may notice that it's just the way from #2

4.Using pkill, kill processes by PGID(Proess Group ID)

pkill -9 -g $PGID

5.Using pkill, kill processes by GID(Group ID)

pkill -9 -G $GID

6.Using pkill, kill processes by PPID(Parent Process ID)

pkill -9 -p $PPID

7.Using pkill, kill processes by terminal

pkill -9 -t $terminal

Note: without /dev/ prefix

8.Using pkill, kill processes by process name

pkill -9 -x $process_name

9.Using pkill, kill processes by session

pkill -9 -s $sess

How to get PID,PGID,sessionid etc?

# ps -o pid,ppid,pgid,gid,sess,cmd -U root
  PID  PPID  PGID   GID  SESS CMD