Cron - Revision history

Ardika Sulistija at 23:52, 14 November 2024

2024-11-14T23:52:06Z

← Older revision		Revision as of 23:52, 14 November 2024
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	* https://crontab.guru/		* https://crontab.guru/
	* https://unix.stackexchange.com/questions/212703/crontab-error-no-crontab-for-use		* https://unix.stackexchange.com/questions/212703/crontab-error-no-crontab-for-use
	https://linuxhandbook.com/crontab/		* https://linuxhandbook.com/crontab/
	* https://serverfault.com/questions/449651/why-is-my-crontab-not-working-and-how-can-i-troubleshoot-it		* https://serverfault.com/questions/449651/why-is-my-crontab-not-working-and-how-can-i-troubleshoot-it

Ardika Sulistija at 23:51, 14 November 2024

2024-11-14T23:51:58Z

← Older revision		Revision as of 23:51, 14 November 2024
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	* https://crontab.guru/		* https://crontab.guru/
	* https://unix.stackexchange.com/questions/212703/crontab-error-no-crontab-for-use		* https://unix.stackexchange.com/questions/212703/crontab-error-no-crontab-for-use
			https://linuxhandbook.com/crontab/
	* https://serverfault.com/questions/449651/why-is-my-crontab-not-working-and-how-can-i-troubleshoot-it		* https://serverfault.com/questions/449651/why-is-my-crontab-not-working-and-how-can-i-troubleshoot-it

Ardika Sulistija at 23:38, 14 November 2024

2024-11-14T23:38:42Z

← Older revision		Revision as of 23:38, 14 November 2024
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	https://serverfault.com/questions/449651/why-is-my-crontab-not-working-and-how-can-i-troubleshoot-it		https://serverfault.com/questions/449651/why-is-my-crontab-not-working-and-how-can-i-troubleshoot-it

	<u>Education about cron:</u>		<u>Education about cron:</u></br>
	Every user on a system may have their own crontab file. The location of the root and user crontab files are system dependant but they are generally below <b>/var/spool/cron</b>.		Every user on a system may have their own crontab file. The location of the root and user crontab files are system dependant but they are generally below <b>/var/spool/cron</b>.

Ardika Sulistija at 23:38, 14 November 2024

2024-11-14T23:38:31Z

← Older revision		Revision as of 23:38, 14 November 2024
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	https://serverfault.com/questions/449651/why-is-my-crontab-not-working-and-how-can-i-troubleshoot-it		https://serverfault.com/questions/449651/why-is-my-crontab-not-working-and-how-can-i-troubleshoot-it

	~~ducation~~ about cron:		<u>Education about cron:</u>
	Every user on a system may have their own crontab file. The location of the root and user crontab files are system dependant but they are generally below <b>/var/spool/cron</b>.		Every user on a system may have their own crontab file. The location of the root and user crontab files are system dependant but they are generally below <b>/var/spool/cron</b>.

Ardika Sulistija at 23:38, 14 November 2024

2024-11-14T23:38:10Z

← Older revision		Revision as of 23:38, 14 November 2024
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	====Notes:====		====Misc. Notes====
	----		----

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	https://serverfault.com/questions/449651/why-is-my-crontab-not-working-and-how-can-i-troubleshoot-it		https://serverfault.com/questions/449651/why-is-my-crontab-not-working-and-how-can-i-troubleshoot-it

			ducation about cron:
			Every user on a system may have their own crontab file. The location of the root and user crontab files are system dependant but they are generally below <b>/var/spool/cron</b>.

			There is a system-wide <b>/etc/crontab</b> file, the /etc/cron.d directory may contain crontab fragments which are also read and actioned by cron. Some Linux distributions (eg, Red Hat) also have <b>/etc/cron.{hourly,daily,weekly,monthly}</b> which are directories, scripts inside which will be executed every hour/day/week/month, with root privilege.

			root can always use the crontab command; regular users may or may not be granted access. When you edit the crontab file with the command <b>crontab -e</b> and save it, <b>crond</b> checks it for basic validity but does not guarantee your crontab file is correctly formed. There is a file called cron.deny which will specify which users cannot use cron. The <b>cron.deny</b> file location is system dependent and can be deleted which will allow all users to use cron.

			If the computer is not powered on or crond daemon is not running, and the date/time for a command to run has passed, crond will not catchup and run past queries.

Ardika Sulistija at 23:35, 14 November 2024

2024-11-14T23:35:55Z

← Older revision		Revision as of 23:35, 14 November 2024
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	PATH=/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin		PATH=/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin
	20 0 * * * root test -x /etc/cron.daily/popularity-contest && /etc/cron.daily/popularity- contest --crond		20 0 * * * root test -x /etc/cron.daily/popularity-contest && /etc/cron.daily/popularity- contest --crond



			====Troubleshooting Cron Jobs====
			----

			https://serverfault.com/questions/449651/why-is-my-crontab-not-working-and-how-can-i-troubleshoot-it

Ardika Sulistija: Created page with " crond - daemon to execute scheduled commands. crontab - Used to schedule repetitive tasks/commands. must be root Good info: * https://cronitor.io/cron-reference/5-places-cron-jobs-live * https://www.geeksforgeeks.org/crontab-in-linux-with-examples/ * https://crontab.guru/ * https://unix.stackexchange.com/questions/212703/crontab-error-no-crontab-for-use * https://serverfault.com/questions/449651/why-is-my-crontab-not-working-and-how-can-i-troubleshoo..."

2024-08-21T14:45:07Z

Created page with " crond - daemon to execute scheduled commands. crontab - Used to schedule repetitive tasks/commands. *must be root* Good info: * https://cronitor.io/cron-reference/5-places-cron-jobs-live * https://www.geeksforgeeks.org/crontab-in-linux-with-examples/ * https://crontab.guru/ * https://unix.stackexchange.com/questions/212703/crontab-error-no-crontab-for-use * https://serverfault.com/questions/449651/why-is-my-crontab-not-working-and-how-can-i-troubleshoo..."

New page

crond - daemon to execute scheduled commands.

crontab - Used to schedule repetitive tasks/commands. *must be root*

Good info:
* https://cronitor.io/cron-reference/5-places-cron-jobs-live
* https://www.geeksforgeeks.org/crontab-in-linux-with-examples/
* https://crontab.guru/
* https://unix.stackexchange.com/questions/212703/crontab-error-no-crontab-for-use
* https://serverfault.com/questions/449651/why-is-my-crontab-not-working-and-how-can-i-troubleshoot-it

====How to use crontab====
----

* /etc/crontab - User specific cron jobs
* /var/log/cron - Logs (You can check this to see if the cronjob is running)

For details see man 4 crontabs

Example of job definition:
.---------------- minute (0 - 59)
| .------------- hour (0 - 23)
| | .---------- day of month (1 - 31)
| | | .------- month (1 - 12) OR jan,feb,mar,apr ...
| | | | .---- day of week (0 - 6) (Sunday=0 or 7) OR sun,mon,tue,wed,thu,fri,sat
| | | | |
* * * * * user-name command to be executed

EXAMPLE CRONTAB:
* At every 12th hour and 30 min, it will run that command.
* If all categories were "*" then it will run the command every minute.
MIN HOUR DOM MON DOW CMD
30 12 * * * /home/ardika/Scripts/first.sh

0 * * * * every hour
*/15 * * * * every 15 mins
0 */2 * * * every 2 hours
0 0 * * 0 every Sunday midnight
@reboot every reboot

Define user, only need this is you are ROOT.
crontab -u

To see what crontabs are currently running.
sudo crontab -l
sudo crontab -u ardika -l

To edit the list of cronjobs you can run.
sudo crontab -e
sudo crontab -u ardika -e

====How I Configured Automated Certificate Renewal====
----

Instructions: https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/SSL-on-amazon-linux-2.html#letsencrypt

Open /etc/crontab in a text editor and add a line similar to the following.
39 1,13 * * * root certbot renew --no-self-upgrade

* Schedules a command to be run at 01:39 and 13:39 every day. The selected values are arbitrary, but the Certbot developers suggest running the command at least twice daily. This guarantees that any certificate found to be compromised is promptly revoked and replaced.
* root - The command runs with root permissions.
* certbot renew --no-self-upgrade - The command to be run. The renew subcommand causes Certbot to check any previously obtained certificates and to renew those that are approaching expiration. The --no-self-upgrade flag prevents Certbot from upgrading itself without your intervention.

Restart the cron daemon.
systemctl restart crond

====Notes:====
----

* Your scheduled cron jobs also run as your main user, but they don't use the PATH settings that your user has. So, if you are running like aws cli from a bash script in your cron, be sure to check PATH: example:
$ cat /etc/cron.d/popularity-contest
SHELL=/bin/sh
PATH=/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin
20 0 * * * root test -x /etc/cron.daily/popularity-contest && /etc/cron.daily/popularity- contest --crond