Re: Switching Crontab Files Via At

also sprach Martin McCormick <martin@xxxxxxxxxxxxxxxxxx> [2006.09.01.2258 +0200]:
The actual crontab file for a given user has a warning
about not editing it directly. When you use crontab -e, the
application takes care of installing the new crontab for the
user and appears to do a kill -HUP on cron to get it to load the
new crontab for that user.

I don't think it sends a SIGHUP. In fact, I don't think it can
because it does not run with root permissions.

Suppose one wants to run a particular crontab while on
vacation or during some other unusual time period and then switch
back to a "normal" crontab. Is it safe to make at cp a new
version of crontab to /var/spool/crontabs/user and then do a KILL
-HUP on cron's PID?

cron will reload automatically every minute.

If you can ensure that there are no syntax errors in the file you
install manually, then yes, it should be safe. The reason why this
note is there is because crontab does syntax checks on the
user-submitted file.

There's also

crontab -l | crontab -

...

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