swarren and I were just chatting and he mentioned putting something into rc.local. I said that I tended to prefer using “@reboot with cron” over rc.local these days. Partly because I don't like rc.local, partly because it keeps most of my system maintenance stuff in one place on my laptop. Stephen hadn't heard about @reboot though…
The cron daemon supports several “@ nicknames” for use instead of the normal set of time values: @reboot, and @hourly (daily, weekly, monthly, yearly/annually).
I use this in my personal crontab for a job I want run once at boot time:
@reboot ~/bin/archivevimswap >/dev/null 2>&1
This is a small shell script that moves my ~/.vim-tmp out of the way and creates a new ~/.vim-tmp. I have vim configured to put all the tmp files in there, so that I don't end up with them littered all over the disc.
Just to be canonical, I'll mention that you can also be lists, ranges, and steps, so things like “*/5 * * * *” is every 5 minutes, “0 9-17 * * *” is the top of the hour from 9am to 5pm, and “15,20 * * * *” runs at 15 and 20 minutes past the hour.
Lately though, I've been thinking about what a next-generation cron would look like. It would be nice to say “I have these 10 jobs that need to be run between midnight and 4am, but I only want 3 of them running at once.” Rather than having to try to stagger them. I could imagine a use for also having it “kill -STOP” jobs if the load goes above a certain value, or “kill -CONT” when it drops. Or even coordination among machines (I have 10 machines, they all need to run CPU-intensive jobs after midnight, but I don't want to cause a spike in power consumption or drop in responsiveness among all of them).
So many possibilities…comments powered by Disqus