How can I fix "MTM fs Mount server failed to start because of error 15"?

Solution 1:

I had the same problem and was due to errors in the localhost's IPv4 address in /etc/hosts. The daemon of mtmfs listening on localhost.

Check that this is the first line in /etc/hosts:

127.0.0.1       localhost

Also you can test: (depends on the firewall options)

$ ping localhost

Then turn off local Time Machine snapshots and trigger automatic cleanup of accumulated local snapshot data :

$ sudo tmutil disablelocal

Reboot the mac, and turn on local Time Machine snapshots:

$ sudo tmutil enablelocal

And it works without errors.

[system.log] mtmfs[40]: mount succeeded for /Volumes/MobileBackups

Solution 2:

I've had miserable luck interacting with mtmfs and fixing things when they go amiss. I do have good success in cleaning out the mobile store and starting the mobile backup portion clean.

Make a time machine backup with your normal destination drive mounted, then disable - let the system clean up the on-disk cache space and then re-enable the local snapshot store. You do lose any backup intervals that are not on the actual destination, but you also get a working set. Lastly, I would run tmdiagnose to capture the failure before you clean up just in case it reappears and you can send both sets of diagnostic logs to Apple for analysis by engineering.

sudo -s
tmutil startbackup --rotation --block
tmdiagnose
tmutil disablelocal
sleep 30
tmutil enablelocal
exit

At this point, you'll want to test a backup or two and repeat the tmdiagnose if you happen to reproduce the issue:

tmutil snapshot
sleep 15
tmutil startbackup --rotation --block
sleep 15
tmutil snapshot