mailboxes.db unreadable, recovery procedure?

[!jeff!{InterVerse}]

Hi List,

I have a cyrus system with only about 20 users on it.  They have about 3 
gigs of mail.

The mailboxes.db file is unreadable.  of course, reconstruct -m is 
unavailable, in typical dougadamsian fashion.

I have seen recommendations to try to 'rebuild the db' using the 
'db.backup1' or 'db.backup2' directories.  I have the dirs.  What specific 
command (including flags) do I use to attempt that?

i have seen use 'ctl_cyrusdb -r' but I keep getting segmentation fault and 
core dump.  I have tried that with and without my corrupted mailboxes.db 
file in place.  what does that tell us?

Since it's such a small system, a backup the mail spool, reinstall, 
recreate user accounts type of approach would work for me if that's the 
simplest thing to do... or just a 'run this command to get a fresh 
mailboxes file'... but I don't know how.

Can somebody please give me a step by step here?

TIA,
Jeff