为什么我的crontab无法正常工作？

Question

I am planning to run some bash scripts every minute, and I wrote:

* * * * * bash ~/Dropbox/temp_scripts/run_all_scripts 

in crontab.

It was supposed to run every minute, but it did not work. Does anyone have idea why this happens?

Answer 1

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Add I/O redirection to the command line in the crontab entry:

>/tmp/run_all_scripts.out 2>/tmp/run_all_scripts.err

Review the contents of the files after a minute or two has passed. Consider recording the environment to see if that's part of the problem. And consider using bash -x instead of just bash .

If you still don't get anything (the files in /tmp are not created), then you've got issues with cron ; the daemon isn't running, or your user does not have permission to use it (but crontab isn't telling you that), or you've not submitted your crontab to the program (what does crontab -l say?), or … whatever is really wrong.

Note, too, that the output from cron jobs is normally (well, at least sometimes — on Mac OS X for a system I currently use, and Solaris for another that I've used previously) emailed to the person whose job it is. You should review the email on the system.

Thank you! I have already fixed it! The reason why it does not work is I used " ls -a .sh " in the script, and when the crontab did not find any *.sh files in the folder it was executing. When modifying it to " ls -a $HOME/Dropbox/temp_scripts/.sh ", everything works! This debugging technique is quite helpful!

It is, in many ways, the most basic of debugging techniques — make sure you see what is actually happening. If you're not sure why a shell script isn't working, make sure you can see that it is executing and what it is producing in the way of output, and (very often) make sure you can see what it is executing with bash -x or equivalent. (AFAIK, all shells support -x to trace the execution.)