It's important that you elaborate on HOW/WHERE you are adding crons. But I think the following addresses any situation.
cron needs to be made aware that you made changes, but no, you don't necessarily need to explicitly do anything to update it.
I'm paraphrasing the
cron manual here for the short version:
crontab -e, the preferred method, will notify
cron that something changed.
cron "wakes up" every minute to see if it has tasks for that minute. It also scans
/var/spool/cron/crontabs and will reload any files with an updated 'mtime' (modified time, meaning the file contents must have been updated).
So theoretically, if you do nothing,
cron will "wake up" and see you made changes to anything directly in
But if you can, use
crontab -e. When you are done editing, it even gives you feedback that it was updated, it says:
crontab: installing new crontab
Specifically, this means that it refreshed its copy in memory for the file you just edited via
Here's a quote from the manual CRON(8) :
cron searches its spool area (/var/spool/cron/crontabs) for
crontab files (which are named after accounts in /etc/passwd);
crontabs found are loaded into memory. Note that crontabs in this
directory should not be accessed directly - the crontab command
should be used to access and update them.