[PHP] endless loop mimics a cron. Make sure only one instance is running


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# 1  
[PHP] endless loop mimics a cron. Make sure only one instance is running

Hi,

PHP user here. I'm using an endless loop to perform to mimic a cron. The script does something every 20 minutes. It sleep()s in the meantime.

I have various checks that ensure that only instance can run, including a "gentleman agreement" locked file.

However, I'd like to make sure that only one instance of the cron script is running. It would also be useful for me to be a 100% certain that the cron script is actually running when it tells me it is.

Can it be done? If yes, how? I have unfortunately no experience in this area.

Regards,

-jj. Smilie
# 2  
Your script has a log file, right? Have it write to the log file after it's finished doing whatever it does, and before it sleeps:

Code:
echo 'date' Done - going to sleep >> /tmp/script.sleep.log


You can then tail -f the log and watch it roll, check the timestamp on it to see when last updated, figure out when it failed, etc.

I usually count processes by doing something like this:

Code:
ps -aef | grep -v grep | grep very_unique_scriptname | wc -l | bc

# 3  
Thank you very much. Smilie

I'm very new to this, so please excuse a fire of questions.

Quote:
Originally Posted by tderscheid
Your script has a log file, right? Have it write to the log file after it's finished doing whatever it does, and before it sleeps:

Code:
echo 'date' Done - going to sleep >> /tmp/script.sleep.log

I hadn't thought about a log file. But it makes sense. However, since the script executes itself every 30 seconds, 8 hours a day, 5 days a week, I guess I would only log failures (if not, I would end up with a huge log file). What would be your approach?

Quote:
Originally Posted by tderscheid
You can then tail -f the log and watch it roll, check the timestamp on it to see when last updated, figure out when it failed, etc.
The tail command reads and print the final lines of an input. So I would basically read the log file, correct?

Quote:
Originally Posted by tderscheid
I usually count processes by doing something like this:

Code:
ps -aef | grep -v grep | grep very_unique_scriptname | wc -l | bc

Very interesting, even though it will take some serious time for a command newbie like me to translate it into an understandable sentence Smilie
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