On Thu, 13 Oct 2005, Ron Yorston wrote:
Matthew Saltzman wrote:
So if you don't want to endure the load of daily maintenance tasks, leave
your machine on. If you don't want to do that, you can adjust the start
time of cron in /etc/crontab and the delay for anacron in /etc/anacron.
Leaving machines switched on 24/7 just so that a cron job can run at 0402
is very wasteful. Also, some hardware components for non-server machines
aren't qualified to run continuously.
Then 24/7 is not the solution. That's why there are alternatives.
Many machines are only switched on when someone want to use them. No
amount of fiddling with cron or anacron will then avoid the problem of
cron jobs running at some inconvenient moment.
Not entirely, but the problem can be mitigated. Run during lunch. Run
after hours and shut down by cron. When do you run backups?
Or, of course, turning it off is always an option.
I wonder if nicing it would avoid the problem of making your machine
unresponsive. I don't see why it has to run at regular priority.
Also, the amount of work prelink does can be controlled in
/etc/sysconfig/prelink. Normally, it should be quick (only bins and libs
that have changed), but every two weeks it runs normally. If you aren't
upgrading RPMs, it apparently doesn't do anything at all until after a
week elapses.
Also, is everyone in on this discussion sure that it is prelink that is
providing the load? slocate.cron can run for a long time on large
filesystems.
Well, I can't speak for everyone, but I'm aware of the different background
tasks that are fired off as cron jobs and of their different characteristics.
Prelink is most objectionable to me because it's more CPU intensive. On
my laptop machine you can tell when prelink starts because the fans turn on
and run continuously for however long it takes. Slocate's updatedb is less
of a concern because it's mostly limited by disk I/O. I also happen to
think that having an up to date slocate database is much more useful to me
than whatever advantages prelink might bring.
That is, of course, your prerogative.
Ron
--
Matthew Saltzman
Clemson University Math Sciences
mjs AT clemson DOT edu
http://www.math.clemson.edu/~mjs
