linux - PID(Process ID) save at start

How to get PID of background process?

I start a background process from my shell script, and I would like to kill this process when my script finishes.

How to get the PID of this process from my shell script? As far as I can see variable $! contains the PID of the current script, not the background process.

• $$ is the current script's pid
• $! is the pid of the last background process

Here's a sample transcript from a bash session (%1 refers to the ordinal number of background process as seen from jobs):

$ echo $$
3748

$ sleep 100 &
[1] 192

$ echo $!
192

$ kill %1

[1]+  Terminated              sleep 100

this is what I have done. Check it out, hope it can help.

#!/bin/bash
#
# So something to show.
echo "UNO" >  UNO.txt
echo "DOS" >  DOS.txt
#
# Initialize Pid List
dPidLst=""
#
# Generate background processes
tail -f UNO.txt&
dPidLst="$dPidLst $!"
tail -f DOS.txt&
dPidLst="$dPidLst $!"
#
# Report process IDs
echo PID=$$
echo dPidLst=$dPidLst
#
# Show process on current shell
ps -f
#
# Start killing background processes from list
for dPid in $dPidLst
do
        echo killing $dPid. Process is still there.
        ps | grep $dPid
        kill $dPid
        ps | grep $dPid
        echo Just ran "'"ps"'" command, $dPid must not show again.
done

Then just run it as: ./bgkill.sh with proper permissions of course

root@umsstd22 [P]:~# ./bgkill.sh
PID=23757
dPidLst= 23758 23759
UNO
DOS
UID        PID  PPID  C STIME TTY          TIME CMD
root      3937  3935  0 11:07 pts/5    00:00:00 -bash
root     23757  3937  0 11:55 pts/5    00:00:00 /bin/bash ./bgkill.sh
root     23758 23757  0 11:55 pts/5    00:00:00 tail -f UNO.txt
root     23759 23757  0 11:55 pts/5    00:00:00 tail -f DOS.txt
root     23760 23757  0 11:55 pts/5    00:00:00 ps -f
killing 23758. Process is still there.
23758 pts/5    00:00:00 tail
./bgkill.sh: line 24: 23758 Terminated              tail -f UNO.txt
Just ran 'ps' command, 23758 must not show again.
killing 23759. Process is still there.
23759 pts/5    00:00:00 tail
./bgkill.sh: line 24: 23759 Terminated              tail -f DOS.txt
Just ran 'ps' command, 23759 must not show again.
root@umsstd22 [P]:~# ps -f
UID        PID  PPID  C STIME TTY          TIME CMD
root      3937  3935  0 11:07 pts/5    00:00:00 -bash
root     24200  3937  0 11:56 pts/5    00:00:00 ps -f

An even simpler way to kill all child process of a bash script:

pkill -P $$

The -P flag works the same way with pkill and pgrep - it gets child processes, only with pkillthe child processes get killed and with pgrep child PIDs are printed to stdout.

source - http://stackoverflow.com/questions/1908610/how-to-get-pid-of-background-process