UNIX for Dummies Questions & Answers

I want to set up a file with crontab to run the cron deamon so I can use at to schedule jobs. I think the crontab file (or whatever you call it) has to be set up. Currently, I don't have a crontab file (I checked by typing sudo crontab -u myusername -l), and I don't know the syntax for creating one. I need to create one that allows at to be run. At the moment at doesn't work. Are there any sources that give information about using crontab or cron? I've tried the man pages and Wikipedia, but neither of them has provided any answers.

Try the following way for creating the crontab. If you have crontab file already it will open the existing file. Otherwise it will create new crontab file.

Code:

crontab -e

It will open the cron file with following line.
# m h  dom mon dow   command

I already know how to create a crontab file. What I want to know is what to put into the file to set it up so that I can use at.

Try the following example.

Code:

* * * * * ls   # This line will execute the 'ls' command at every time for every day.

If you want better understanding try the following link.
Link : Crontab – Quick Reference.

Code:

crontab -e

Crontab -e option is used to edit the crontab file. if the file already exist then it will open the existing file otherwise it will create a new file in your /tmp directory.
-l option is used for to list the crontab entries
-r option is used for to remove the crontab entries

crontab entry format:

m h dom mon dow command


* * * * * command to be executed
- - - - -
| | | | |
| | | | +----- day of week (0 - 6) (Sunday=0)
| | | +------- month (1 - 12)
| | +--------- day of month (1 - 31)
| +----------- hour (0 - 23)
+------------- min (0 - 59)

The crontab file has nothing to do with at. at and cron can be configured separately to be allowed or denied for users.

I found that link helpful and have been able to successfully set up a crontab file. Thank you for your replies.