which one is better Run by Cron or Shell

thepurple · #1 (**permalink**) 01-03-2009

Dear Experts,

I have a script defined in Cron which runs every 1 minute.

Code:

* * * * * /export/home/myscript.sh >/dev/null 2>&1

Now the issue is executing that myscript.sh sometime will take 2/3 or more minutes to finish execution.

But after 1 minute cron will invoke another instance(process) execute the myscript. In that case do you think there is a probability to overlapping the instance and may create problem.

If there is a chance for overlapping may be the below shellscript(run it in background) is okay which will run every 1 minute. Script will invoke different instant after every minute.

Code:

#!/usr/bin/bash
while :
do
    sleep 60 & pid=$!
    /export/home/myscript.sh
    wait $pid
done

Could you please make your valuable suggestion?

//purple

Panos1962 · #2 (**permalink**) 01-03-2009

There is another solution to this problem, but you have to add some code to your `myscript.sh'. Put some kind of lock while your program is runing, e.g. if your program is a shell script, you can add the following lines:

Code:

...
lock=/export/home/.myscript.lock
trap "rmdir ${lock}; exit 2" 1 2 3 15
# Now lock. If lock fails, then propably the program is runing.
mkdir ${lock} || exit 0
...
Here comes the script code
...
# Now unlock, so another instance of this program can run in the future.
rmdir ${lock}

I prefer this kind of coding in such cases, because it's better to protect this kind of programs to run overlaping processes. So, either you prefer cron, or sleeping nohup shell scripts, the process is vulnerable to run in simultaneus instances; if you use some kind of locking this is impossible.
Bye...

2k7.vipin · #3 (**permalink**) 01-03-2009

Can you try this way

#!/usr/bin/bash
while :
do
/export/home/myscript.sh
pid=$!
wait $pid
done

thepurple · #4 (**permalink**) 01-03-2009

Quote:

Originally Posted by Panos1962

Code:

...
lock=/export/home/.myscript.lock
trap "rmdir ${lock}; exit 2" 1 2 3 15
# Now lock. If lock fails, then propably the program is runing.
mkdir ${lock} || exit 0
...
Here comes the script code
...
# Now unlock, so another instance of this program can run in the future.
rmdir ${lock}

is it just like..

Code:

#!/usr/bin/bash
lock=/export/home/.myscript.sh.lock
trap "rmdir ${lock}; exit 2" 1 2 3 15

mkdir ${lock} || exit 0
...
Here comes my script code
...
rmdir ${lock}

After that i can put the script in Crontab.

In that case every 1 minute cron will invoke process and child process. But meanwhile, the program (myscript) can be running with different process and child process id.

right?

//purple

thepurple · #5 (**permalink**) 01-03-2009

moreover,

let say myscript.sh is running and having the below process id-

solaris:/home/user1> ps -ef|grep myscript.sh
solaris 25907 10427 0 14:36:50 ? 0:00 /export/home/myscript.sh

i put the myscript.sh in cron as 1 minute interval. So, every 1 minute interval solaris again run the myscript.sh.

DO you think solaris May try to assing the next myscript.sh with procss id 25907( which indicating overlapping)?
procss id 25907 still running.....

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