A laptop is powered off most nights, so the nightly maintenance jobs scheduled by plain cron never run. Which mechanism is designed to catch up such missed periodic jobs after the machine is next started?
LPIC-1 Exam 102-500, objective 107. Administrative tasks medium
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The options
Not correct atd
Wrong. atd executes one-off at jobs. If the machine is down at the scheduled moment, atd runs the job when it next starts, but it has no notion of daily, weekly or monthly periods and it is not what schedules routine maintenance.
Not correct run-parts
Wrong. run-parts is only a helper that executes every executable script in a directory, which is how /etc/cron.daily and friends are triggered. It has no scheduling or catch-up logic of its own.
Correct anacron
Correct. anacron schedules jobs by period in days rather than by clock time, records in /var/spool/anacron when each job last ran, and on start runs anything whose period has elapsed — after an optional delay in minutes.
Not correct crond with the @reboot keyword
Wrong for this purpose, though @reboot is real: it runs a job once each time cron starts up. It cannot tell whether a daily job was actually missed, so it would fire on every boot regardless.
Why
An /etc/anacrontab line has four fields: period in days, delay in minutes, a job identifier, and the command. Many distributions wire cron.daily, cron.weekly and cron.monthly through anacron precisely so that desktop and laptop machines still get their maintenance. anacron does not run jobs more often than once per period and has no sub-day granularity.
Where this comes from
- Cited
- LPI exam objective 107.2
- What it says
- Understand the purpose of anacron on systems that are not running continuously.
Practise this
Reading one question is not practice. The trainer will draw a set from objective 107 and space the ones you get wrong.