anacron deliberately doesn't run if the machine is running on battery
power. This is fine if the only jobs are "housekeeping" tasks that
it's safe to skip, but if you have critical jobs like backups then it's
not so good. This is a dangerous situation as users are unlikely to
notice that this feature exists until it's too late, e.g. when they
want to recover something from a backup.
I suggest:
1. This feature needs to be documented, at the very least in
README.Debian. Actually looking at bug #83334 message #40 a patch was
submitted that added "anacron will avoid running while the system is
battery powered" to that file, but that either never made it in to the
package or it has subsequently been removed. But I don't think
documentation alone is sufficient, as users familiar with anacron from
non-laptops will be able to set up their jobs without referring to any
documentation and won't learn about this feature (until it's too late).
2. There needs to be some way to enable or disable this feature, and
I'd suggest that it should be disabled by default. A debconf question
and/or /etc/default/anacron variable would be a possible method.
3. Better than a global enable/disable setting would be to indicate
that some jobs are deferrable, and should only be run on ac power, and
others are critical and should be run unconditionally. This could be
done using different directories or a naming convention.
A related problem is that some jobs may require network connectivity
while others don't. I can imagine a scheme where job names include
tags, e.g.
/etc/cron.daily/man_db--acpower - only run when on ac power, doesn't
need network
/etc/cron.daily/backup--net - run even when on battery, only if
network is up
You can specify a job pattern on the anacron command line to specify
the tags to match in the current run.
Regards, Phil.
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