the blkid manpage says:
-w <writecachefile> Write the device cache to
writecachefile instead of writing it to the default
cache file /etc/blkid.tab. If you don?t want to save
the cache to the default file, specify /dev/null.
If not specified it will be the same file as that
given by the -c option.
and yet, since:
http://thunk.org/hg/e2fsprogs/?rev/ad62cded89a8 (I think...)
(2003...) it has been completely ignored.
I have a bug on this, from before my time at Red Hat,
https://bugzilla.redhat.com/show_bug.cgi?id=200191 Bugzilla Bug 200191:
blkid does not rewrite blkid.tab as documented in the man page.
...filed in 2006.
It'd be easy enough to fix, although this might be a library API change,
at least if we want to make blkid_get_cache() symmetric with
blkid_put_cache(), each taking a filename...
But it's been broken so long, with (few) complaints, is the
functionality worth resurrecting, or should I just submit a patch to
remove the -w option? :)
Thanks,
-Eric