$USER1$/check_disk -w 5G -c 1G -p /data/foo

If you don’t actually test that this works (by artificially filling your disk and seeing what happens), you may be dismayed to find that you only get alerted when the disk has 5MB of free disk space. Why is this?

Because Nagios, despite the fact that nobody has sweated the megabytes for about a gazillion years, doesn’t support ‘G’ as a suffix for thresholds. Oh, it’ll make a good show of pretending — after all, the output formatting options have ‘GB’ as an option — but nope, for your thresholds it’s “5000M” all the way.

ROCK ON!