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anacron

Ubuntu anacron package, installed by default.

anacrontab

Configures anacron.

Line format:

period delay job-identifier command

Fields separated by tabs or spaces.

Every day as soon as anacron starts:

1 0 test.daily sleep 3 && date >> /tmp/anacrontest

Command run environment

Try:

1 0 test (date; id; pwd; env) >> /tmp/anacrontest

Runs:

  • as user root
  • from directory /

If we do a:

pstree

and start killing things, we see that;

  • anacron is the parent of the processes it spawns
  • killing anacron does not kill it's children
  • when all children exit, anacron then exits

anacron command

Run anacron commands that haven't been run yet on their time-slots:

sudo anacron

sudo is mandatory, I think because jobs run as root.

For execution of jobs now, even before their time:

sudo anacron -f

s

By default, each anacron line is run asynchronously. Try:

1 0 test1 sleep 3 && echo a >> /tmp/anacrontest
1 0 test2 sleep 1 && echo b >> /tmp/anacrontest

and then:

sudo anacron -f

Then /tmp/anacrontest contains:

b
a

But if we had done:

sudo anacron -fs

it would contain instead:

sudo anacron -

Ubuntu implementation

In Ubuntu 15.10, cron calls anacron periodically via the crontab entries:

# m h dom mon dow user	command
17 *	* * *	root    cd / && run-parts --report /etc/cron.hourly
25 6	* * *	root	test -x /usr/sbin/anacron || ( cd / && run-parts --report /etc/cron.daily )
47 6	* * 7	root	test -x /usr/sbin/anacron || ( cd / && run-parts --report /etc/cron.weekly )
52 6	1 * *	root	test -x /usr/sbin/anacron || ( cd / && run-parts --report /etc/cron.monthly )

Those take care of the case where the computer has been left running for a long time, and run things in the morning.

Anacron is also run whenever the computer starts up, or resumes from sleep. I think those implemented by the files:

/etc/apm/event.d/anacron
/etc/init/anacron.conf

which the anacron package installs.

By default, anacron does on Ubuntu:

1	5	cron.daily	run-parts --report /etc/cron.daily
7	10	cron.weekly	run-parts --report /etc/cron.weekly

So packages can use files in those directories to install anacron scripts.

/var/spool/anacron

Stores the date in which commands were last run:

sudo tail -n+1 /var/spool/anacron/*

Sample output:

==> /var/spool/anacron/cron.daily <==
20151207

==> /var/spool/anacron/cron.monthly <==
20151202

==> /var/spool/anacron/cron.weekly <==
20151207

==> /var/spool/anacron/test.daily <==
20151207

==> /var/spool/anacron/test1 <==
20151207

==> /var/spool/anacron/test2 <==
20151207