Cron Timing

Murdock1979 · 08-05-2008, 04:04 AM

Hello!

I am wondering does a cronjob start another process if the job is triggered although the previous process has not yet finished yet? For example, a job is set to run every ten minutes and when ten minutes pass, the previous process is still running. So does the cronjob wait or just start a new process.

Is there any way to control this?

Thanks,
Murdock

colucix · 08-05-2008, 04:30 AM

It starts a new process, despite a process with the same name or launched from the same crontab entry is still running. There are a lot of ways to control it, depending on the type of application and the ability to modify the executable. For example if it is a shell script you can put a "waiting" loop at the beginning of the script:

Code:

#!/bin/bash
while ps -C name_of_the_process > /dev/null
do
  sleep 5
done

This will repeatedly sleep 5 seconds until the previous process is terminated. Anyway, you may end up with multiple processes waiting for each other. If this is the case, maybe it's better to schedule the process with a longer time step.

chrism01 · 08-05-2008, 09:21 AM

cron resolution is only to the nearest minute: http://www.adminschoice.com/docs/cro...Crontab%20file .
If you want better than that, write your own daemon (infinite loop) and just wait (eg sleep 10) if you want a minimum num of seconds between runs.

kenoshi · 08-05-2008, 05:25 PM

Control it through your script, tried and true way would be:

Code:

if [ -e /tmp/already_started ]; then

   echo "I am already running as $(< /tmp/already_started), exiting" >> /tmp/some_error_log
   exit 1
    
else

   echo $$ > /tmp/already_started
   do_your_thang
   rm -f /tmp/already_started
   
fi

ladoma · 09-27-2011, 04:02 PM

Quote:

Originally Posted by kenoshi

Control it through your script, tried and true way would be:

Code:

if [ -e /tmp/already_started ]; then

   echo "I am already running as $(< /tmp/already_started), exiting" >> /tmp/some_error_log
   exit 1
    
else

   echo $$ > /tmp/already_started
   do_your_thang
   rm -f /tmp/already_started
   
fi

Thank you very much!! That was exact the code i was looking for.
Because to install flock ect. on my linkstation, my knowledge wasn't good enough ;-)

I am using(now) a linkstation mini(LS-WSGL) with rsync, that automatically sync to my online-storage(Strato Hidrive).

I edit my cronjob like this:

Code:

cd /etc/cron
crontab -e

I added following line:

Code:

*/1 * * * * /mnt/array1/share/rsync_hidrive_setup.sh

My rsync_hidrive_setup.sh looks like this:

Code:

#!/bin/bash

if [ -e /mnt/array1/share/already_started ]; then

   echo "I am already running as $(< /tmp/already_started), exiting" >> /tmp/some_error_log
   exit 1
    
else

   echo $$ > /mnt/array1/share/already_started
   rsync --delete --exclude=.* -avubzre ssh -i /root/.ssh/id_rsa /mnt/array1/share/rsync BENUTZER@rsync.hidrive.strato.com:/users/BENUTZER --backup-dir=deleted_rsync
   rm -f /mnt/array1/share/already_started
   
fi