Hello, I'm responsible for about 30 Ubuntu computers at a private K-8 school. We have only a 3Mbps internet connection serving the entire campus, and I would like to ensure that updates are done in the middle of the night - so that daytime tasks are not slowed down.

I'm using Ubuntu 10.04, and have set all computers to download and install security updates via the update manager. I have also installed cron-apt, and modified the config file to stagger the start times of the upgrades from about 10pm to 4am local time.

HOWEVER - this morning I arrived at the school at 7:30am and all the computers were busy downloading a large security based update. Needless to say, all internet activity was slowed to a crawl (for the next 2 hours), and the computer users were very very upset. This was the event I'm trying so hard to prevent.

It seems that my scheme to ensure middle of the night downloads failed, and I'm not sure why.

I've also tried some schemes using unattended-upgrades & crontab, but there always seemed to be something scheduling upgrades to occur in addition to the ones I try to force at middle of the night.

Is there a sure fire way to absolutely positively guarantee that updates will occur only at one specific time? It would be nice if the update manager just had a drop down menu to specify a designated time.

Thanks in advance for any help you can give me.