What is Anacron?
A cron alternative that runs missed scheduled jobs when the system comes back online.
Definition
Anacron (anachronistic cron) is a periodic command scheduler that does not assume the system is running continuously. If a scheduled job was missed because the system was powered off or asleep, anacron runs it when the system next starts. Unlike cron, anacron only handles daily or longer intervals (not hourly or minutely). It uses /etc/anacrontab for configuration, with each entry specifying a period in days, a delay in minutes, a job identifier, and a command.
Simple Analogy
Like a personal assistant who checks your to-do list every morning — if you were away yesterday, they catch up on anything you missed before starting today's tasks.
Why It Matters
Laptops, development machines, and intermittently connected servers frequently miss cron jobs because the system was off or asleep at the scheduled time. Anacron ensures critical maintenance tasks — log rotation, backups, package updates — still execute. For always-on servers, cron is sufficient, but for any system with downtime, anacron provides essential catch-up scheduling.
How to Verify
Check if anacron is installed with "which anacron" or "anacron -V". View its configuration at /etc/anacrontab. The timestamps in /var/spool/anacron/ show when each job last ran. On modern systems, anacron is often triggered by cron itself via /etc/cron.daily/0anacron.
Common Mistakes
Relying on anacron for minute or hour-level scheduling — it only supports daily or longer periods. Assuming anacron replaces cron entirely — they are complementary tools. Not setting appropriate delays between anacron jobs, causing all missed tasks to run simultaneously at boot.
Best Practices
Use anacron for daily maintenance tasks on systems that may not run 24/7 (laptops, dev servers). Keep cron for always-on production servers and minute/hour-level scheduling. For critical production jobs, use CronJobPro which handles missed schedules automatically with configurable retry policies.
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What is Anacron?
Anacron (anachronistic cron) is a periodic command scheduler that does not assume the system is running continuously. If a scheduled job was missed because the system was powered off or asleep, anacron runs it when the system next starts. Unlike cron, anacron only handles daily or longer intervals (not hourly or minutely). It uses /etc/anacrontab for configuration, with each entry specifying a period in days, a delay in minutes, a job identifier, and a command.
Why does Anacron matter for cron jobs?
Laptops, development machines, and intermittently connected servers frequently miss cron jobs because the system was off or asleep at the scheduled time. Anacron ensures critical maintenance tasks — log rotation, backups, package updates — still execute. For always-on servers, cron is sufficient, but for any system with downtime, anacron provides essential catch-up scheduling.
What are best practices for Anacron?
Use anacron for daily maintenance tasks on systems that may not run 24/7 (laptops, dev servers). Keep cron for always-on production servers and minute/hour-level scheduling. For critical production jobs, use CronJobPro which handles missed schedules automatically with configurable retry policies.
Related Terms
Cron
A time-based job scheduler built into Unix and Linux operating systems.
Cron Daemon
The background process that continuously checks and executes scheduled cron jobs.
Missed Schedule
A scheduled execution that did not fire at its intended time due to downtime or errors.
Systemd Timer
A Linux systemd unit that schedules services to run at specified times, as an alternative to cron.