Finding process id of subsequent process

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# 8  
Old 11-06-2009
thmnetwork - many thanks for the continued reply

this is how it goes,
envVarSetter dataCrunch.exe

I can only capture the pid of envVarSetter and not the pid of dataCrunch.exe as the latter would be spawned as the child of envVarSetter and not as the child of main spawner / controller

So collecting pid here
1) is not useful for checking the status of process whether its running or not
2) or for creating a lock files because lock file would be created before the actual process is spawned.

For ex:

This is how the process is spawned in sequence.
echo $running_no > $lock_file ; envVarSetter dataCrunch.exe; rm $lock_file

Here, how can I fit the usage of pids here.
If I have not explained properly or improperly please do let me know

thanks Smilie
# 9  
Old 11-06-2009
I'm going to add more to this post later, but one idea would be to spawn another process in your serialized command there that does nothing but wait a second and then quickly looks for the envVarSetter located underneath your parent script, and take its pid out that way. Or you may find your solution by leveraging process grouping (I'm assuming from "init" that this is unix anyways.)


Ok, experimenting with perl child processes a bit on Aix 5.2 it looks like both tty and nice values are inherited by children even after the parent gets cruelly kill -9'd.

This opens the door for possible additional differentiation if you launch envVarSeter via the "nice" command. in additon to time, command, and username(if variable) criteria you can add the tty (if variable) and a randomly generated nice value. You could even store the last three or four generated nice values. That requires a collision to be between dataCrunchers launched with three or four others in the same second, under the same username, on the same tty, and with the same randomly generated nice value. I think that sufficiently would shrink the collision domain for us unless you have one hellacious load level. After you find the PID by the criteria after the fact you can re-adjust the nice's to production levels.

The main obstacle I can see is if envVarSetter clobbers the nice value. You'll probably want to find a way to run the command from the command line in a non-destructive way. Not sure what dataCruncher.exe or envVarSetter are so you're probably on your own as far as whether "coding the nice level" will work. If you could find something within process groups that works, that would probably be more ideal for you.

Last edited by thmnetwork; 11-06-2009 at 08:33 PM..
# 10  
Old 11-09-2009
probably process group is a nice idea. I will try evaluating in that domain.

Regarding nice value, tty inheritance - there is a potential problem if I rely on them.

I am trying to frame a generic script and the multiple chunks that are being executed, needlessly might turn out to a be a daemon therefore

1) detaching itself from a tty
2) altering the nice value
3) can switch between multiple process groups

the above is not something frequent but the generic capability of the script will be affected.

Am really wondering, is n't there an easy way to track child process by the parent - condition being parent is short lived and child being inherited by init.

Thanks again Smilie
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