Fixing the Time Machine / Time Capsule 10.5 "Backup volume could not be mounted" bug

After some network revisions and machine migrations It was time to clear out some Time Capsule backups. Alas, there's no documentation on how one can do this. Even the excellent Take Control of OS X Backups eBook has no advice on removal of an entire machine backup. [Update: Joe Kissell, the author, responded almost instantly to an email. I've updated my post on freeing up TC storage with his response (that post also summarizes TC documentation).]

The best advice I could find is to erase the Time Capsule disk. I have other backups, so I went ahead. That part went well.

My 10.6 machine resumed its Time Machine backups with no problems. My 10.5 machines, however, complained that the "Backup volume could not be mounted".

Turns out this is a known 10.5 bug -- an unfixed10.5.3 bug.

• Mac OS X 10.5.3 or later: Time Machine - "Backup volume could not be mounted" after changing network volume's password
• Time Capsule: Time Machine backups do not mount
• Mac OS X 10.5: Time Machine - "The backup volume could not be found" alert

I had success with

• Open Time Machine preferences
• Click "Select Disk"
• Reselect the Time Capsule disk.

I was then asked to enter a user name and password -- but dialog showed only a password (bug). I think user name in this context is really the machine name. I'd enabled guest access so I clicked "guest" and the backup resumed.

Note that since Apple fixed this in 10.6 but not 10.5, it's an example of a bug that can drive new machine purchases (older machines can't run 10.6). Bundling backup with the OS wipes out the alternatives, and since backup is essential unfixed bugs can be very profitable for Apple. This one, at least, is relatively easy to work around.

See also:

• Time Machine: Fail first, then flaw discovered - a more obscure bug in 10.6
• Freeing up Time Capsule space – and documentation for Time Machine and Time Capsule
• Time Machine: Troubleshooting backup issues