I want to run my ruby script x times a day (the number might change) on my linux box. What would be the best way to do so if I do not want it to happen at the same time? I want the time (hour and minute) to be random
I was thinking of using at command. The script would be called by at in x hours/minutes or so and then the script would set up another call by at. Not sure if there is any better way or only ruby way.
I guess you can setup a cronjob that calls on a bash script which delays execution by a random time but I don't know if you can do it somehow inside the cronjob. You can find some information on how to do that on this site and if you don't know about crontab and cronjobs you can find more information about that here.
I'd consider using the at program to run the programs (instead of using cron directly, because cron really only works on a fixed schedule). I'd also create a program (I'd use Perl; you'll use Ruby) to schedule a random delay until the next time the job is executed.
You'll need to consider whether it is crucial that the job is executed 'x' times in 24 hours, and how the randomness should work. What is the range of variation in times. For example, you might have a cron job run at midnight plus 7 minutes, say, which then schedules 'x' at jobs spaced evenly through the day, with a random deviation in the schedule of ±30 minutes. Or you might prefer an alternative that schedules a the jobs with an average gap of 24/x hours and a random deviation of some amount. The difference is that the first mechanism guarantees that you get x events in the day (unless you make things too extreme); the second might sometimes only get x-1 events, or x+1 events, in 24 hours.
If you want to run X times a day, set your crontab entry to:
0 */X * * * command_to_run
where X is the hourly interval you want to fire your job on to get the desired number of executions/day. For instance, use 2 to fire off every two hours for a total of 12 executions/day.
In your code use this at the top to force it to sleep a random time up to that cron interval:
# How long the program takes to run, in seconds. Be liberal unless having # two instances running is OK. EXECUTION_TIME = 10 INTERVAL = 2 * 60 * 60 - EXECUTION_TIME sleep(rand(INTERVAL))
The idea is that cron will start your program at a regular interval, but then it will sleep some random number of seconds within that interval before continuing.
Change the value for EXECUTION_TIME to however long you think it will take for the code to run, to give it a chance to finish before the next interval occurs. Change the "2" in the INTERVAL to whatever your cron interval is.
I haven't tested this but it should work, or at least get you on the right path.
I think scheduler solutions are bit limiting, to get most flexible random action, turn your script to daemon and code the loop / wait yourself.
For Ruby there seems to be this: http://raa.ruby-lang.org/project/daemons/