The initial run of overviewer seemed to work well. Yesterday, I re-enabled the cron job to update the map every day at midnight. When I got up this morning, I discovered that the server had died at 00:16.
I restarted the server and tried updating the map by running overviewer from the command line, and the server switched off abruptly after a few minutes with no error messages.
There’s nothing in the logs, and the server doesn’t just die, it powers off. The most likely cause is that the processor is overheating, but it seems odd that it completed the initial build during several days of triple-digit temperatures with server room temps reaching the mid 80’s, and last night the temp in the server room was in the low 70’s. But CPU fans and cooling paste can fail over time, and perhaps overviewer actually taxes the processor more when most blocks are already up-to-date.
Right now the server is running, but the maps won’t be updated until at least the weekend when I have a few moments to troubleshoot.