vacuum process is hanging

Greetings,
I've got an 8.1.10 instance running on Linux-i686. The system hosts 5
databases, all of which get vacuumed via a cronjob 3 times a day. All
of a sudden, the vacuum job for 1 of the databases is hanging
indefinitely. It normally finishes in under 5 minutes. There are no
errors in the output, it just stops producing any output. The command
that I'm running is "vacuumdb -v -z -f -d inventory". I also tried
removing the -z and -f options to see if that would at least get it to
complete, but that had no impact. Here's the tail end of the output,
leading up to the hang:

INFO: vacuuming "public.cuhc"
INFO: index "cuhc_system_key" now contains 0 row versions in 4 pages
DETAIL: 1 index pages have been deleted, 1 are currently reusable.
CPU 0.00s/0.00u sec elapsed 0.00 sec.
INFO: index "cuhc_system_index" now contains 0 row versions in 4 pages
DETAIL: 1 index pages have been deleted, 1 are currently reusable.
CPU 0.00s/0.00u sec elapsed 0.00 sec.
INFO: index "cuhc_syststamp_index" now contains 0 row versions in 4 pages
DETAIL: 1 index pages have been deleted, 1 are currently reusable.
CPU 0.00s/0.00u sec elapsed 0.00 sec.
INFO: index "cuhc_syststamprebooted_index" now contains 0 row
versions in 4 pages
DETAIL: 1 index pages have been deleted, 1 are currently reusable.
CPU 0.00s/0.00u sec elapsed 0.00 sec.
INFO: "cuhc": found 0 removable, 0 nonremovable row versions in 0 pages
DETAIL: 0 dead row versions cannot be removed yet.
There were 0 unused item pointers.
0 pages are entirely empty.
CPU 0.00s/0.00u sec elapsed 0.00 sec.
INFO: vacuuming "pg_toast.pg_toast_85894"
INFO: index "pg_toast_85894_index" now contains 0 row versions in 1 pages
DETAIL: 0 index pages have been deleted, 0 are currently reusable.
CPU 0.00s/0.00u sec elapsed 0.00 sec.
INFO: "pg_toast_85894": found 0 removable, 0 nonremovable row
versions in 0 pages
DETAIL: 0 dead row versions cannot be removed yet.
There were 0 unused item pointers.
0 pages are entirely empty.
CPU 0.00s/0.00u sec elapsed 0.00 sec.

Anyone have any suggestions on what to try to debug this?

thanks!