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How to ignore jobs already running in cron

Posted on 2015-01-30
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Last Modified: 2015-02-02
Hi , Is there a way i can ignore the run of a scheduled cron job if the jobs is already running on the host.

I am asking this because I have a cron entry to run a job every minute. Sometimes the script completes within a minute, some time goes more than a minute. When it runs more that a minute the next scheduled run tries to execute the script and this results in an cron error.
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Question by:naveenraj
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by:Rob_Jeffrey
ID: 40579841
You can write a wrapper script around the job which checks the existence of a file then if it doesn't exist, make the file, run your command, then delete the file.
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Expert Comment

by:gheist
ID: 40580815
Run it every 2 minutes or get a faster system?
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Rob_Jeffrey earned 2000 total points
ID: 40580877
An example script that can be modified to suit your needs:
#!/bin/sh
FILE=~/job_running.txt
if [ ! -f $FILE ]
then 
  touch $FILE
  echo "Running job"
  # Add command here
  rm $FILE
else 
  echo "Job already running"
fi

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by:Carlos Ijalba
ID: 40581227
As Rob Jeffrey has recommended, whenever we write a script that can be run in parallel (ie: multiple runs of the same script), we should always check if our script is already running and exit the script.

This is done either by using a flag file, or checking the process list with a ps command.

Note that if you use a flag file, you should also intercept interruption signals (ie: TRAPS) so if the script gets killed by a CTRL-C, or a kill command, it ends up in a controlled manner and deletes the flag file, otherwise if the script fails, you will have a permanent flag and next runs of the script will always fail until the flag file gets removed manually. (And of course document the flag file location and use for operators or other sysadmins).
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Expert Comment

by:gheist
ID: 40581366
Just put it in a loop?
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