All of my nodes seem to have rebooted simultaneously at 6:25am on the last two Sundays.

One of my co-workers called customer support, and they said that it was us that caused the restart, but there is nothing that I know of that we are doing that would cause them all to reboot at the same time. Even if I wanted to do it I doubt I could.

Check your control panel logs, that'll tell you if the reboot came from the panel or from the operating system itself. If it's from the panel, I think support should be able to tell you what IP logged in and scheduled the job. If it's from the OS, you'll need to check that out.

Hmmm - no indication of a restart there. It looks like 6:25 is when my daily cron maintenance job runs, maybe the Ubuntu default install has a reboot on Sunday or something.

Reboots from inside would still show up in the Linode Manager; they would show as 'Lassie initiated boot' in the Host Job Queue.

What makes you say there was a restart? You can check whether it actually restarted by running 'uptime'.