How can I fix "MTM fs Mount server failed to start because of error 15"? For the last few weeks, I've been getting lots of recurrent MTM fs Mount server failed to start because of error 15 error messages in system.log. How can I diagnose and fix this?

I don't know if it's causing any issues, but it's worrisome, and it's spamming the log file so I'm having trouble diagnosing other problems. Time Machine has also been wonky lately, failing to complete backups to external drives attached to my Time Capsule because it couldn't find the backup disk. (Backups to locally-attached drives work fine.) Maybe related, since mtmfs is part of the Time Machine system.

Here's what it looks like, from system.log as viewed in Console. There will be a sequence of errors and restart attempts, which then get throttled.

Nov 28 15:08:18 eilonwy.local mtmfs[379]: cannot bind custom tcp socket
Nov 28 15:08:18 eilonwy.local mtmfs[379]: MTM fs Mount server failed to start because of error 15
Nov 28 15:08:19 eilonwy.local mtmfs[379]: MTM fs Mount server retrying ...
Nov 28 15:08:19 eilonwy.local mtmfs[379]: cannot bind custom tcp socket
Nov 28 15:08:19 eilonwy.local mtmfs[379]: MTM fs Mount server failed to start because of error 15
Nov 28 15:08:21 eilonwy.local mtmfs[379]: MTM fs Mount server retrying ...
Nov 28 15:08:21 eilonwy.local mtmfs[379]: cannot bind custom tcp socket
Nov 28 15:08:21 eilonwy.local mtmfs[379]: MTM fs Mount server failed to start because of error 15
Nov 28 15:08:22 eilonwy.local mtmfs[379]: MTM fs Mount server retrying ...
Nov 28 15:08:22 eilonwy.local mtmfs[379]: cannot bind custom tcp socket
Nov 28 15:08:22 eilonwy.local mtmfs[379]: MTM fs Mount server failed to start because of error 15
Nov 28 15:08:24 eilonwy.local mtmfs[379]: MTM fs Mount server retrying ...
Nov 28 15:08:24 eilonwy.local mtmfs[379]: cannot bind custom tcp socket
Nov 28 15:08:24 eilonwy.local mtmfs[379]: MTM fs Mount server failed to start because of error 15
Nov 28 15:08:25 eilonwy.local mtmfs[379]: MTM fs Mount server retrying ...
Nov 28 15:08:25 eilonwy.local mtmfs[379]: MTM fs Mount server failed to start because of too many retries
Nov 28 15:08:25 eilonwy.local mtmfs[379]: MTM fs Mount server failed, last error 15
Nov 28 15:08:25 eilonwy com.apple.launchd[1] (com.apple.mtmfs[379]): Exited with code: 99
Nov 28 15:08:25 eilonwy com.apple.launchd[1] (com.apple.mtmfs): Throttling respawn: Will start in 3 seconds


This repeats constantly, ending up with about 150,000 mtmfs error messages in system.log every day.

This is on OS X 10.8.5 on a Mid 2012 Retina MacBook Pro. eilonwy is the hostname of my machine.

I've looked through what little doco on mtmfs I've found through man and Google, and while it tells how to start and stop it, I've found no info on what error 15 means, what "custom tcp socket" it might be trying to bind to and how to fix, and what the consequences of mtmfs not running are.

I contacted Apple support and they suggested doing a "Repair Permissions" from Disk Utility, which I did and it didn't fix the problem, and then reinstalling OS X, which is a little aggressive (and Windows-y) for my taste.

Can anyone help me fix this, or point at some resources to help diagnose it?
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