I was running make to build Comedi against the current Hardy kernel, and it died with

...
make[1]: Warning: File `Makefile' has modification time 1.1e+02 s in the future
make[1]: Nothing to be done for `clean-am'.
make[1]: warning:  Clock skew detected.  Your build may be incomplete.
make[1]: Leaving directory `/thor/wking/src/lab/comedi/comedi-build'
make: warning:  Clock skew detected.  Your build may be incomplete.

“No problem,” thinks I, since I'd just rebooted into the new kernel, but I'd pulled the source in under the old kernel. I'll just touch all the files to make sure their times are in the past.

Nope. Same error. Turns out my touch is from the future:

$ date; ll include/Makefile; touch include/Makefile; ll include/Makefile; date
Fri May  8 10:48:35 EDT 2009
-rw-r--r-- 1 wking wking 15540 2009-05-08 10:48 include/Makefile
-rw-r--r-- 1 wking wking 15540 2009-05-08 10:50 include/Makefile
Fri May  8 10:48:35 EDT 2009

This is because my files are NFS mounted from another computer, and the clocks were out of sync by two minutes. Time to setup NTP for the lab LAN ;).