Is grandchild process also child process

Do you mean all processes started by some process (have the same parent PID)?

If you have pgrep you can filter all the processes with the same parent ID:

top -p $(pgrep -P 2069 -d,)

If not you can filter all process ids through awk and use them with top -p:

top -p $(ps -eo pid,ppid |awk '($2==2069){printf "%s%s",delim,$1; delim=","}')

Change $2==2069 with the actual parent pid you want to track.

#!/bin/sh
#This is a process with an id of $$

( sleep 1000 )&               #this creates an idle child
( (sleep 1000)& sleep 1000 )& #this creates an idle child and grandchild
wait                          #this waits for direct children to finish

Running the above as ./1.sh & on my system created the following process tree:

$ command ps -o pid,ppid,pgrp,stat,args,wchan --forest
  PID  PPID  PGRP STAT COMMAND                     WCHAN
24949  4783 24949 Ss   /bin/bash                   wait
25153 24949 25153 S     \_ /bin/sh ./1.sh          sigsuspend
25155 25153 25153 S     |   \_ sleep 1000          hrtimer_nanosleep
25156 25153 25153 S     |   \_ sleep 1000          hrtimer_nanosleep
25158 25156 25153 S     |       \_ sleep 1000      hrtimer_nanosleep

You can notice that the tree has the same process group (PGRP) of 25153, which is identical to the PID of the first process. The shell creates a process group whenever you start a new command in interactive mode (or with job control explicitly turned on).

The PGRP mechanism allows the shell to send a signal to the whole process group at once without creating a race condition. This is used for job control, and when your script runs and a foreground job, for sending:

• (SIG)INTR when the user presses C-C
• (SIG)QUIT when the user presses C-\
• (SIG)STP when the user presses C-Z

You can do the same by doing, for example:

kill -INTR -25153 

where INTR is the signal and 25153 is the process group you want to send the signal to. The - before the 25153 means you're targeting a PGRP id rather than a PID.

In your case, the signal you should be sending is -TERM (request termination). Term is the default signal kill sends, however, you have to specify it explicitly if you're targeting a group rather than a PID.

kill -TERM -25153

If you want to kill the process group of the last background job you started, you can do:

kill -TERM -$!