Consider the following scenario:
Let's say I have a cronjob running every 3 hours (0 */3 * * *).
The job just ran 2 minutes ago.
If I were to reboot my computer right after it runs, will the cronjob remember that it just ran ~2 minutes ago, or will it run directly after it boots?
Neither.
It doesn't need to remember that it just ran. The job runs at 0:00 03:00, 06:00, etc. If the system isn't up at the scheduled time, the job doesn't run.
If the job ran at 03:00 and you reboot at 03:02, the job won't run again until 06:00.
(If you want jobs to run if they couldn't run before because the system was down, see anacron.)
Related
I want to limit the korn job to run between 10 pm to 12 am.Currently it was taking more time to complete than the time frame. Even if its not finished , it as to terminate.
You can write a cron job, that runs on 12 am. It can look for your job and kill it.
Without a cron job you can do the same with timeout.
Another approach is having your script to look at the clock and call some abort() function a few seconds before 12 am.
This solution relies on the assumption, that your script is in some long loop, and you can add a function call at a central point (or some central points) where the script will be every few seconds. Using timeout seems to be better, but now you can stop your script in a controlled way (and timeout is unaware of changes in the clock, the DST or rdate).
Say, I have scheduled a script to run after every 3 mins. The Cron job runs the script first time and now, after 3 mins. it will try to run the script again, but the script is already running from the first instance and that the processing is still not complete. What will happen than - will it run the script again as a second instance.
Yes (unless the script itself takes measures to prevent a second instance from running).
Cron just runs a command on a schedule.
If that command starts a program, it starts a program.
I am currently working on a web application and I want to schedule a method that runs every day at 6 AM. Basically, if the clock ticks at 6 AM, this method will run. I have seen some answers on the Internet but none of these are scheduled at a fixed time of the day but rather timed after the app is ran.
I also have an alternative solution which is to check every minute if the time is 6 AM, and if so, I'll run the code. But is there other better answer than this?
Thank you!
On the server side, you could do it with a cron job.
On Linux follow these steps:
crontab -e
Here's an example of how to make a request to the google.com at 6AM (UTC)
# Each day at 6th hour (6 AM depending on your time zone settings, or UTC)
0 6 * * * curl -I http://google.com
:wq # save changes and quit
:q # to quit
:q! # to quit without saving changes
See more about Cron here. Or use a visual crontab entry creator if that is helpful. If you need a solution for Windows machine, you could also use a Windows scheduler to trigger events similar to cron.
Cron job would be a good way of doing it. However, for some reason if you can not schedule a cron job and need your own scheduler and your environment is Java based then you could use the Quartz Scheduler. It is a java based job scheduler like cron. It's usage is pretty simple.
I have a cron job set to run a script once a day at 3am.
0 3 * * * /home/path/script.pl
It's been running without any problems since April 11th. Last weekend though, on Saturday the 3rd of May, the script was called once a minute for 24 hours. (1441 times in total) Then afterwards, on the 4th and 5th, it went back to only being called once a day at 3:00 again.
Does anyone have any ideas as to why this happened? I was wondering if there was an error in my crontab, since I have a 3 in it, and it was the 3rd of May that it happened. Since I only started running the cron since the 11th of April, I have no idea if it's something that will happen once a month on the 3rd, or if it was a one time thing unrelated at all.
I looked around and didn't find anything related, so I though I'd just ask while I continued to tried to find out what happened. I currently changed the cron to make it run at 6am instead to see if I'd end up with the same thing again tomorrow.
0 6 * * * /home/path/script.pl
EDIT
Everything was working fine, but then again on the 3rd of June, the same thing happened again. Could this be related to a cron problem or could it be something else entirely?
The problem was finally solved. There was a second cron being executed by root that was incorrectly written, which was making the script be called once a minute on the 3rd of the month instead of once a day at 3am.
The cron did not show up with the other cron jobs, and only by using the following command
did the cron job actually appear.
grep script /var/spool/cron/crontabs/*
I still don't understand but it's working correctly now.
I Have crontab set up (on my local MacOSX system) to run a job on a per hourly basis. It runs fine. I am not sure if it is possible, but is there a way that I can run the job for 'missing' hours (in case my computer sleeps or I shut it down)?
For example if cronjob ran fine for hours (1-13) before I shut down the system. I start up the system again after, lets say 2 hours. Is there a way to tell cron to run the job for missing hours (14,15) too before executing hour 16?
The cronjob currently running fills up some data in my local MySQL DB with hour information in one of the columns. Any tips, tricks or libraries will be helpful.
Thanks.
Maybe have a look at anacron for Mac that can catch up jobs missed while your Mac was sleeping the next time it wakes up. See here.