iB::Topic::Keeping Cron job from eating itself

	Damn Small Linux :: Damn Small Linux Board The DSL Forums

» Welcome Guest
[ Log In :: Register ]

Damn Small Linux Board » Non-DSL Topics » Programming and Scripting » Keeping Cron job from eating itself

		Mini-ITX Boards Sale, Fanless BareBones Mini-ITX, Bootable 1G DSL USBs, 533MHz Fanless PC <-- SALE $200 each!
		Get The Official Damn Small Linux Book. DSL Market , Great VPS hosting provided by Tektonic

Pages: (2) </ [1] 2 >/

[ Track this topic :: Email this topic :: Print this topic ]

Topic: Keeping Cron job from eating itself

< Next Oldest | Next Newest >

jerekeib

Group: Members
Posts: 6
Joined: July 2006

Posted: Oct. 27 2006,01:23

I have a cron job that runs a shell script every 2 minutes that wgets several files and compiles an image via imagemagik.

This job normally takes about 30 seconds, but once in a great while it takes longer than the 2 minutes (due to internet congestion or far end server problems) and thus cron starts a duplicate script. Things get worse from there and usually x aborts and I have to restart.

How do I keep cron from executing the script in the event the last one hasn't finished?

Thanks for any light you can shed in this!

mikshaw

Group: Members
Posts: 4856
Joined: July 2004

Posted: Oct. 27 2006,03:10

I wouldn't bother with cron for something done that frequently.
If you want a 2 minute pause every time, you could put your commands in a function, with the last 2 commands of that function be a 2-minute sleep and then a call to itself.

There's probably a better way, but that at least would prevent overlapping.

--------------
http://www.tldp.org/LDP/intro-linux/html/index.html

lstark

Group: Members
Posts: 8
Joined: Oct. 2006

Posted: Oct. 27 2006,04:06

I would edit your script so that it checks to see if an instance of itself is already running. [Personally I'd do this by 'grep'ing and 'awk'ing the process list for your processes PID. If it returns a number its running, otherwise it isn't running. Then with the added info of the PID you can choose to kill the currently running instance if you think its taking too long]. Otherwise if your script is already running, just exit out of the script (or take some other alternative measure besides executing the wget and/or whatever else it does).

lstark

Group: Members
Posts: 8
Joined: Oct. 2006

Posted: Oct. 27 2006,04:16

just realized i said something stupid. If you check the process list you will always have at least one instance of your script running since the script has to be active to be doing the check.

Therefore, count the number of lines that are returned. 1 line means only this instance of the script is running, >1 line means there are other instances already running.

mikshaw

Group: Members
Posts: 4856
Joined: July 2004

Posted: Oct. 27 2006,04:18

Another possibility....
Check for a particular pid file name, which would rid you of the need to grep and awk the process list. If the pid file exists, exit. If the file does not exist, create the file, do your business, remove the file, and exit.

It doesn't even need to be a pid file. Any uniquely named temp file would work.

--------------
http://www.tldp.org/LDP/intro-linux/html/index.html

5 replies since Oct. 27 2006,01:23

< Next Oldest | Next Newest >

[ Track this topic :: Email this topic :: Print this topic ]

Pages: (2) </ [1] 2 >/

Damn Small Linux Board » Non-DSL Topics » Programming and Scripting » Keeping Cron job from eating itself