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i want to execute a script twice daily at 00:00 and 13:30 so i write :
0,30 0,13 * * * it seems wrong for me, because like this, the script will fire at 00:00 , 00:30 , 13:00 and 13:30. Any idea ?
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0 * * * * -this means the cron will run always when the minutes are 0 (so hourly) 0 1 * * * - this means the cron will run always at 1 o'clock. * 1 * * * - this means the cron will run each minute when the hour is 1.
We can run several commands in the same cron job by separating them with a semi-colon ( ; ). If the running commands depend on each other, we can use double ampersand (&&) between them. As a result, the second command will not run if the first one fails.
The basic usage of cron is to execute a job in a specific time as shown below. This will execute the Full backup shell script (full-backup) on 10th June 08:30 AM. Please note that the time field uses 24 hours format. So, for 8 AM use 8, and for 8 PM use 20.
Try this-: 00 01,13 * * *
it will run at 1 A.M and 1 P.M
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You can't do what you want in one entry, since the two minute definitions will apply for both hour definitions (as you've identified).
The solution is (unfortunately) use two cron entries. One for 00:00 and one for 13:30.
An alternative is perhaps to execute one script at 00:00. That script would execute your original script, then wait 13.5 hours and then execute that script again. It would be easy to do via a simple sleep command, but I think it's unintuitive, and I'm not sure how cron manages such long running processes (what happens if you edit the crontab - does it kill a spawned job etc.)
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