How to detect what is causing entries in the "last" cmd's output? last ... date { Sun Mar 31 12:00 date | Sun Mar 31 12:00 date { Sun Mar 31 00:00 date | Sun Mar 31 00:00 ... Why are there e.x.: "{" in the last commands output? Some sort of script could do this? (on OpenBSD 5.1)

The lines you are seeing indicate the system time has been automatically updated. The '|' character indicates the time prior to the change and the '{' character indicates the new time.

Source: man utmp (5)