Mac OS X is able to do some maintenance every once in a while. Therefore some maintenance scripts are started during the night. If you mac isn't launched at that time the scripts won't be started.

But you can start them manually:

Start the Terminal and enter:

% sudo periodic daily
% sudo periodic weekly
% sudo periodic monthly

You can view the launch of these scripts by opening the cron:

cat /etc/crontab

The maintenance scripts are visible by typing:
cat /etc/daily,
cat /etc/weekly
et cat /etc/monthly

:-)

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