After I enter my password, sudo -k will extend the 5 minute limit on that password entry to "the Epoch" (whenever that may be), but only for that one command?
No, it's the other way around. The "epoch" for Unix is Jan 1, 1970 at 00:00:00 GMT. The 5-minute window during which the previous password entry is still valid becomes the 5 minutes starting then.
The practical effect is to make the old password entry expire immediately, even if its normal 5-minute lifetime still has time to run.
Here's an example session (with
comments) that was run through in less than a minute:
ronk@Zebra:~(0)$ su -l admin # first, become an admin
Password:
admin@Zebra:~(0)$ sudo echo x # first use of sudo requires password
Password:
x
admin@Zebra:~(0)$ sudo echo x # second use does not
x
admin@Zebra:~(0)$ sudo -k # kill the timer
admin@Zebra:~(0)$ sudo echo x # so now I need a password again
Password:
x
admin@Zebra:~(0)$ sudo echo x # the second password is still good
x
admin@Zebra:~(0)$ logout # I'm done being an admin
ronk@Zebra:~(0)$
