Finding the Process ID of a Process While Initiating the Process

senthilmuthiah · 03-27-2009, 09:00 AM

Dear All:

I have a program in java which I execute using a shell script. I would like to find the process id of this java process immediately after execution so that I could kill it downstream somewhere. I was browsing through pgrep/grep etc., However, the problem here is, since this is a java process the name of the process itself is given as "Java" (which I came to know after using the 'top' command. So, I can't use pgrep/grep/ps since there would be other java processes running in the system which I wouldn't dare to even touch!

So, I was wondering whether there is a way by which I could extract the Process ID while I initiate the process itself [as I know there is no way by which I can assign a PID for my forked process]!

Any help would be appreciated!

Thanks in advance!

ilikejam · 03-27-2009, 10:13 AM

Hi.

The PID of the last process spawned in your shell is put in '$!', so:

Code:

#!/bin/bash

java mainclass &
JAVAPID=$!
...
kill $JAVAPID

Dave

MensaWater · 03-27-2009, 10:15 AM

From the bash man page:

Quote:

$ Expands to the process ID of the shell. In a () subshell, it expands to the process ID of the current shell, not the sub-shell.

! Expands to the process ID of the most recently executed background (asynchronous) command.

So if you type:
echo $$ - it will show you PID of current shell.

If you then ran a background process like:
while true; do ls -l; sleep 300; done &
and then typed:
echo $! - it will show you the PID of the while loop above.

senthilmuthiah · 03-27-2009, 10:23 AM

Thanks a lot jlightner and ilikejam. You guys are wonderful!

Both the solutions are working.

Thank you very much!

senthilmuthiah · 04-01-2009, 01:57 PM

Hi jlightner and ilikejam! Seems, there is a small problem here:

I have a script like the following:

ssh -f abc@xyz.edu 'cd /home/abc/; nohup java RunSim '$toSimulate' & JAVAParent='$!' ; echo '$JAVAParent' > ParentPID.txt; pgrep -u '$useid' -P '$JAVAParent' > SimulationPID.txt'

Basically, the script runs a java program (RunSim, which in itself initiates another java program) in a client xyz. I wanted the process id of this parent process so that I could get the PID of the child process through pgrep/ps.

When I debug the script using bash -x, I found that $! wasn't given any value => JAVAParent was empty! Any idea of how I could get through this?

Looking forward to your replies very much!

ilikejam · 04-01-2009, 02:05 PM

I'm assuming that $toSimulate and $useid are set on the machine you're sitting at, not on xyz.edu, so you'd want them to be evaluated before the command is sent over. I'm also assuming there's no spaces in the values of those variables.

ssh -f abc@xyz.edu 'cd /home/abc/; nohup java RunSim '$toSimulate' & JAVAParent=$! ; echo $JAVAParent > ParentPID.txt; pgrep -u '$useid' -P $JAVAParent > SimulationPID.txt'

Dave

senthilmuthiah · 04-02-2009, 10:19 AM

Thank you very much ilikejam!

That problem is gone, however, there is a new one propping up!

The ParentPID.txt is written well while the SimulationPID.txt has nothing in it. I executed
pgrep -u <userid> -P <ParentIDwritteninParentPID> SimulationPID.txt
separately in the client and it does seem to give me the correct PID of the child.

Is it because the SimulationPID.txt is created even before the child process is started? If yes, is there any way by which I could extract this information?

Also, just to make it clear, can you describe what you mean by 'evaluate' in this discussion (It would also help some newb who is viewing this thread.)

Thanks in advance!

senthilmuthiah · 04-02-2009, 10:37 AM

Quote:

Originally Posted by senthilmuthiah

Thank you very much ilikejam!

That problem is gone, however, there is a new one propping up!

The ParentPID.txt is written well while the SimulationPID.txt has nothing in it. I executed
pgrep -u <userid> -P <ParentIDwritteninParentPID> SimulationPID.txt
separately in the client and it does seem to give me the correct PID of the child.

Is it because the SimulationPID.txt is created even before the child process is started? If yes, is there any way by which I could extract this information?

Also, just to make it clear, can you describe what you mean by 'evaluate' in this discussion (It would also help some newb who is viewing this thread.)

Thanks in advance!

So, the problem was indeed what I had mentioned, I gueess: I am writing SimulationPID.txt even before the child process is initiated (so as expected, I don't get anything).

I included a "sleep 5m" in between the two commands and now I see it!

Thank you all for all the help. I love LQ!