Shell script- how to restart applications?

zx712 · 01-29-2011, 01:54 PM

Hello,

I have two applications: p1 and p2.
I need to ensure that p2 keeps running while p1 is running.
If p2 completes before p1, I need to restart p2.

While( p1 is still running)
do
run p2
done

Can someone tell how to do that?

Thank you

stress_junkie · 01-29-2011, 02:02 PM

You could have a script that starts both jobs and that monitors both jobs. That script could restart p2 if required.

ta0kira · 01-29-2011, 02:03 PM

I know there have been many threads similar to this in this forum in the past. They had to do with automatically restarting a crashed process, which is essentially the same thing.
Kevin Barry

zx712 · 01-29-2011, 03:45 PM

Please provide an example.

stress_junkie · 01-29-2011, 04:02 PM

Quote:

Originally Posted by zx712

Please provide an example.

No. You have been given the concept. You should be able to implement it on your own. If you try to implement it and run into problems then show your work and explain what you are having trouble with.

The concept is completely trivial.

zx712 · 01-29-2011, 04:14 PM

Quote:

Originally Posted by stress_junkie

No. You have been given the concept. You should be able to implement it on your own. If you try to implement it and run into problems then show your work and explain what you are having trouble with.

The concept is completely trivial.

How can I check whether or not p1 is still running?

I tried this:

P1 &
pid1=$! #this is id of the first process

While( the status of pid1 is not zero) #how do I get the status of pid1?
do
run p2
done

ta0kira · 01-29-2011, 04:15 PM

Here are a few related threads:
http://www.linuxquestions.org/questi...cation-841731/
http://www.linuxquestions.org/questi...h-help-641783/
http://www.linuxquestions.org/questi...h-bash-769488/

Here's a one-liner for bash, though:

Code:

{ { program1; kill 0; } 1>&3 | while true; do program2 < /dev/null; done; } 3>&1

Kevin Barry

ta0kira · 01-29-2011, 04:26 PM

Quote:

Originally Posted by zx712

I tried this:

P1 &
pid1=$! #this is id of the first process

While( the status of pid1 is not zero) #how do I get the status of pid1?
do
run p2
done

Provided you only have P1 in the background, you don't need the process number; jobs will list the background processes for you.

Code:

P1 &

while jobs | grep -cq .; do
  P2
done

There are two differences between this and my previous post:

This won't kill P2 when P1 exits; my one-liner will
This won't allow P1 foreground access to the terminal; my one-liner will

Either can easily be made into a daemon script. Neither allow for P1 to be started independently of the script, though.
Kevin Barry

PS One-line version of this one is straightforward:

Code:

P1 & while jobs | grep -cq .; do P2; done

zx712 · 01-29-2011, 04:51 PM

Quote:

Originally Posted by ta0kira

Provided you only have P1 in the background, you don't need the process number; jobs will list the background processes for you.

Code:

P1 &

while jobs | grep -cq .; do
  P2
done

There are two differences between this and my previous post:

This won't kill P2 when P1 exits; my one-liner will
This won't allow P1 foreground access to the terminal; my one-liner will

Either can easily be made into a daemon script. Neither allow for P1 to be started independently of the script, though.
Kevin Barry

PS One-line version of this one is straightforward:

Code:

P1 & while jobs | grep -cq .; do P2; done

Thank you very much.