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Cron files are located at:<br />
Debian: sudo cat /var/spool/cron/crontabs/*
===Linux cron tab format===
MIN HOUR DOM MON DOW CMD<br />
MIN HOUR DOM MON DOW CMD<br />
{| class="wikitable"
{| class="wikitable"
|-
|-
! Field !! Description !! Allowed Value
!Field!!Description!!Allowed Value
|-
|-
| MIN || Minute || 0-59
|MIN||Minute||0-59
|-
|-
| HOUR || Hour || 0-23
|HOUR||Hour||0-23
|-
|-
| DOM || Day of Month || 1-31
|DOM||Day of Month||1-31
|-
|-
| MON || Month || 1-12
|MON||Month||1-12
|-
|-
| DOW || Day of the week || 0-6
|DOW||Day of the week||0-6
|-
|-
| CMD || Command || Any command to execute
|CMD||Command||Any command to execute
|}
|}
=== view/edit crontab ===
===view/edit crontab===
$ crontab -l → To view crontab
$ crontab -l → To view crontab
$ crontab -e → Edit crontab
$ crontab -e → Edit crontab
$ crontab -u otherusername -e → Edit other user crontab
$ crontab -u otherusername -e → Edit other user crontab
=== Schedule a job for a specific day ===
===Schedule a job every X minutes===
*/5 * * * * /home/ramesh/backup.sh # Every 5 minutes
*/10 * * * * /home/ramesh/backup.sh # Every 10 minutes
===Schedule a job for a specific day===
example: 10th June 08:30 AM.
example: 10th June 08:30 AM.
30 08 10 06 * /home/ramesh/full-backup
30 08 10 06 * /home/ramesh/full-backup
*30 – 30th Minute
*30 – 30th Minute
*08 – 08 AM
*08 – 08 AM
*10 – 10th Day
*10 – 10th Day
*06 – 6th Month (June)
*06 – 6th Month (June)
* * – Every day of the week</pre>
*<nowiki>* – Every day of the week</nowiki>
=== Schedule a job twice a day ===
===Schedule a job twice a day===
00 11,16 * * * /home/ramesh/bin/incremental-backup
00 11,16 * * * /home/ramesh/bin/incremental-backup
*00 – 0th Minute (Top of the hour)
*00 – 0th Minute (Top of the hour)
*11,16 – 11 AM and 4 PM
*11,16 – 11 AM and 4 PM
* * – Every day
*<nowiki>* – Every day</nowiki>
* * – Every month
*<nowiki>* – Every month</nowiki>
* * – Every day of the week
*<nowiki>* – Every day of the week</nowiki>
=== Schedule a job during working hours ===
===Schedule a job during working hours===
00 09-18 * * * /home/ramesh/bin/check-db-status
00 09-18 * * * /home/ramesh/bin/check-db-status
*00 – 0th Minute (Top of the hour)
*00 – 0th Minute (Top of the hour)
*09-18 – 9 am, 10 am,11 am, 12 am, 1 pm, 2 pm, 3 pm, 4 pm, 5 pm, 6 pm
*09-18 – 9 am, 10 am,11 am, 12 am, 1 pm, 2 pm, 3 pm, 4 pm, 5 pm, 6 pm
* * – Every day
*<nowiki>* – Every day</nowiki>
* * – Every month
*<nowiki>* – Every month</nowiki>
* * – Every day of the week
*<nowiki>* – Every day of the week</nowiki>
=== Schedule a job during working hours excluding Saturday and Sunday ===
===Schedule a job during working hours excluding Saturday and Sunday===
00 09-18 * * 1-5 /home/ramesh/bin/check-db-status
00 09-18 * * 1-5 /home/ramesh/bin/check-db-status
*00 – 0th Minute (Top of the hour)
*00 – 0th Minute (Top of the hour)
*09-18 – 9 am, 10 am,11 am, 12 am, 1 pm, 2 pm, 3 pm, 4 pm, 5 pm, 6 pm
*09-18 – 9 am, 10 am,11 am, 12 am, 1 pm, 2 pm, 3 pm, 4 pm, 5 pm, 6 pm
* * – Every day
*<nowiki>* – Every day</nowiki>
* * – Every month
*<nowiki>* – Every month</nowiki>
*1-5 -Mon, Tue, Wed, Thu and Fri (Every Weekday)
*1-5 -Mon, Tue, Wed, Thu and Fri (Every Weekday)
=== Cron jobs special codes ===
===Cron jobs special codes===
{| class="wikitable"
{| class="wikitable"
|-
|-
! Keword !! Equivalent
!Keword!!Equivalent
|-
|-
| @yearly || 0 0 1 1 *
|@yearly||0 0 1 1 *
|-
|-
| @daily || 0 0 * * *
|@daily||0 0 * * *
|-
|-
| @hourly || 0 * * * *
|@hourly||0 * * * *
|-
|-
| @reboot || Run at startup.
|@reboot||Run at startup.
|}
|}
@yearly /home/ramesh/red-hat/bin/annual-maintenance
@yearly /home/ramesh/red-hat/bin/annual-maintenance
@daily /home/ramesh/arch-linux/bin/cleanup-logs "day started"
@daily /home/ramesh/arch-linux/bin/cleanup-logs "day started"
@reboot CMD
@reboot CMD
===Adding paths to cron jobs===
Add the following line to crontab to specify the location of the scriptss (/home/user/scripts) <br />
This will allow to avoid having to type the full path to the script
PATH=/bin:/sbin:/usr/bin:/usr/sbin:/home/user/scripts
===Enable logging to /var/log/cron.log===
Add to /etc/rsyslog.d/50-default.conf the line:
cron.* /var/log/cron.log
Save and restart rsyslog service
sudo systemctl restart rsyslog
sudo systemctl restart cron
==Examples==
===WF0006D3===
<syntaxhighlight lang="bash">
0 9-17 * * * if [ -d "/media/rafa/GIT/" ]; then /home/rafa/.virtualenvs/git_mirror/bin/python /home/rafa/PycharmProjects/git_mirror/mirror.py work;else echo "$(date) GIT not connected" >> /home/rafa/PycharmProjects/git_mirror/logs/errors.log;fi && /home/rafa/PycharmProjects/Misc/docker_mirror/mirror.sh;fi
0 9-17 * * * if [ -d "/media/rafa/GIT/" ]; then rsync -avp /home/rafa/Downloads/Backups/ /media/rafa/GIT/Wikis/;fi
30 16 * * * scp wiki-tc11.s01.rra.lan:/tmp/wikibackup-$(date +"%Y-%m-%d").tar.gz /home/rafa/Downloads/Backups/attack_wiki/
30 16 * * * scp wiki.rra.lan:/tmp/wikibackup-$(date +"%Y-%m-%d").tar.gz /home/rafa/Downloads/Backups/wiki/
</syntaxhighlight>