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| − | == Overview ==
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| − | Cron is driven by a '''crontab''' (cron table) file, a configuration file that specifies [[Unix shell|shell]] commands to run periodically on a given schedule. The crontab files are stored where the lists of jobs and other instructions to the cron [[Daemon (computer software)|daemon]] are kept. Users can have their own individual crontab files and often there is a system-wide crontab file (usually in <code>/etc</code> or a subdirectory of <code>/etc</code>) that only system administrators can edit.
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| − | Each line of a crontab file represents a job, and looks like this:
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| − | <pre>
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| − | # ┌───────────── minute (0 - 59)
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| − | # │ ┌───────────── hour (0 - 23)
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| − | # │ │ ┌───────────── day of the month (1 - 31)
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| − | # │ │ │ ┌───────────── month (1 - 12)
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| − | # │ │ │ │ ┌───────────── day of the week (0 - 6) (Sunday to Saturday;
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| − | # │ │ │ │ │ 7 is also Sunday on some systems)
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| − | # │ │ │ │ │
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| − | # │ │ │ │ │
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| − | # * * * * * command to execute
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| − | </pre>
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| − | The syntax of each line expects a cron expression made of five fields, followed by a shell command to execute.
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| − | == Logging ==
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| − | Cron execution logs can be saved to specific file using [[rsyslog]] service.
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| − | * In [[Ubuntu]] uncomment in <code>/etc/rsyslog.d/50-default.conf</code> the line:
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| − | :<code>#cron.* /var/log/cron.log</code>
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| − | : and restart rsyslog service: <code>sudo systemctl restart rsyslog</code>
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| − | * In [[Debian]] uncomment in <code>/etc/rsyslog.conf </code> the line:
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| − | :<code>#cron.* /var/log/cron.log</code>
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| − | == Configuration ==
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| − | * <code>[[systemctl]] edit cron.service</code>
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| − | * <code>[[systemctl status cron]]</code>
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| − | /etc/cron.deny (echo ALL >>/etc/cron.deny)
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| − | /etc/cron.allow
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| − | [[/var/]]spool/cron/crontabs/
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| − | == Examples ==
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| − | Execute every minute:
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| | * * * * * /scripts/script.sh | | * * * * * /scripts/script.sh |
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| − | Execute every 5 minutes:
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| − | */5 * * * *
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| − | 45 18 * * * /scripts/script.sh
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| − | @reboot /scripts/script.sh
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| − | == Related terms ==
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| − | * [[Timer (systemd)]]
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| − | * [[kron (Cisco IOS)]]
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| − | * [[TeamCity triggers]]
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| − | * [[GitLab scheduled pipelines]]
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| − | * [[Travis]] cron jobs: https://docs.travis-ci.com/user/cron-jobs/
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| − | * [[Cronitor]] service
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| − | * <code>[[cron.schedule]]</code> [[PostgreSQL]]
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| − | * <code>[[CRON_TZ]]</code>
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| − | * <code>[[ScheduleExpression]]</code> in <code>[[AWS::Events::Rule]]</code>
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| − | * <code>[[pg_cron]]</code>
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| − | * <code>[[.timer]]</code>, <code>[[/lib/systemd/system/]]</code>
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| − | * <code>[[gcloud scheduler]]</code>
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| | == See also == | | == See also == |
| | * {{cron}} | | * {{cron}} |
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| − | [[Category:Server administration]]
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| − | [[Category:Operating systems]]
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| − | [[Category:Linux]]
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| − | {{CC license}}
| + | [[Category:Linux]] |
| − | Source: wikiversity
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