Bad file descriptor

[Walter Hurry]

FreeBSD 9.2-RELEASE

I have a handful of files in a subdirectory of /usr/ports/multimedia/
gstreamer/work, which show up as 'Bad file descriptor'. It appears that I 
am unable to delete them.

/usr/ports is on my root partition/slice, which is ufs with journalling.

On rebooting, it says the partition/slice is clean, so checking is 
skipped.

I gather that the way to fix this is to run fsck with the -f option. Is 
this correct? If so, how do I get / unmounted? Or is there a way to force 
a check on reboot before mounting?