This is a Python script to log when a computer is on.
Execute it, and it produces a sqlite database with two tables, "up" and "down". One records times at which the computer came up, the other times at which it went down.
This script is intended to be invoked on system startup.
Ideally one could simply record all "on" and "off" events at the time they occurred, including boot, reboot, suspend, hibernate, etc. However, this is very system-dependent and always non-exhaustive (for example, sudden loss of power is never recorded).
The simpler solution employed here is to log at intervals the fact that the computer is up. To avoid growing the log at every interval, this script always replaces the last recorded "up" time with a new one, if the last one was recent enough to assume that no intermittent downtime occurred.
If these updates were done through simple file I/O, a sudden power off during an update could cause the loss of uptime information for the last up period. For this reason, logging is done transactionally with sqlite.
Consequently, this will cause periodic disk I/O.