apropos mtmfs(8) – Apple's Mobile Time Machine file system daemon

[grahamperrin]

There's the traditional manual page for mtmfs, and there's mention of local Time Machine snapshots in the manual page for tmutil, but here – running release candidate build 16A319 of Mac OS X 10.12 (macOS Sierra) with a MacBookPro11,2 notebook:

• no local snapshots
• unless I'm missing something, nothing relevant in the Time Machine pane of System Preferences.

sh-3.2$ date ; sw_vers ; uname -a
Sun 18 Sep 2016 15:03:19 BST
ProductName:    Mac OS X
ProductVersion:    10.12
BuildVersion:    16A319
Darwin momh167-gjp4-macbookpro112-sierra.local 16.0.0 Darwin Kernel Version 16.0.0: Mon Aug 29 17:56:20 PDT 2016; root:xnu-3789.1.32~3/RELEASE_X86_64 x86_64
sh-3.2$ apropos mtmfs
mtmfs(8)                 - Mobile Time Machine file system daemon
sh-3.2$ which mtmfs
sh-3.2$ man mtmfs
sh-3.2$ man tmutil
sh-3.2$ ls -ahl /
total 189
drwxr-xr-x   35 root          wheel   1.2K 18 Sep 10:49 .
drwxr-xr-x   35 root          wheel   1.2K 18 Sep 10:49 ..
-rw-rw-r--    1 root          admin   6.0K 16 Sep 01:21 .DS_Store
d--x--x--x    9 root          wheel   306B 17 Sep 17:22 .DocumentRevisions-V100
drwxr-xr-x@   3 root          wheel   102B 17 Sep 01:27 .PKInstallSandboxManager-SystemSoftware
drwx------    5 grahamperrin  staff   170B  8 Sep 16:39 .Spotlight-V100
drwxrwxrwt@   3 grahamperrin  staff   102B  9 Sep 00:36 .TemporaryItems
d-wx-wx-wt    2 grahamperrin  staff    68B  9 Sep 00:39 .Trashes
-rw-r--r--@   1 grahamperrin  staff     0B  8 Sep 16:39 .com.apple.timemachine.donotpresent
----------    1 root          admin     0B 30 Jul 20:32 .file
drwx------  169 grahamperrin  staff   5.6K 18 Sep 13:55 .fseventsd
-rw-------    1 root          wheel    64K  8 Sep 16:58 .hotfiles.btree
drwxr-xr-x@   2 root          wheel    68B 14 Sep 22:03 .vol
drwxrwxr-x+  40 root          admin   1.3K 18 Sep 12:07 Applications
drwxrwxr-x   11 root          admin   374B 16 Sep 01:20 Incompatible Software
drwxr-xr-x+  59 root          wheel   2.0K 18 Sep 10:49 Library
drwxr-xr-x@   2 root          wheel    68B 14 Sep 22:03 Network
drwxr-xr-x@   4 root          wheel   136B 14 Sep 21:54 System
drwxr-xr-x    6 root          admin   204B 14 Sep 22:03 Users
drwxr-xr-x@   7 root          wheel   238B 18 Sep 13:07 Volumes
drwxr-xr-x@  38 root          wheel   1.3K  2 Sep 05:30 bin
drwxrwxr-t@   2 root          admin    68B 14 Sep 22:03 cores
dr-xr-xr-x    3 root          wheel   4.4K 17 Sep 17:21 dev
lrwxr-xr-x@   1 root          wheel    11B 14 Sep 22:00 etc -> private/etc
dr-xr-xr-x    2 root          wheel     1B 18 Sep 10:55 home
-rw-r--r--@   1 root          wheel   313B 31 Jul 03:00 installer.failurerequests
dr-xr-xr-x    2 root          wheel     1B 18 Sep 10:55 net
drwxr-xr-x    4 root          wheel   136B 18 Sep 10:55 opt
drwxr-xr-x@   6 root          wheel   204B 14 Sep 22:03 private
drwxr-xr-x@  63 root          wheel   2.1K 14 Sep 22:01 sbin
lrwxr-xr-x@   1 root          wheel    11B 14 Sep 22:00 tmp -> private/tmp
drwxr-xr-x@  11 root          wheel   374B 16 Sep 01:38 usr
lrwxr-xr-x@   1 root          wheel    11B 14 Sep 22:01 var -> private/var
sh-3.2$

 

[KALLT]

Are you sure that it is enabled? When snapshots are disabled, the Time Machine panel in System Prefs will not mention it. There is no GUI option to disable this.

sudo tmutil enablelocal   # enable snapshots
sudo tmutil snapshot      # make snapshot
defaults read /Library/Preferences/com.apple.TimeMachine MobileBackups   # toggles description

 

[grahamperrin]

For this, a test of a clean-ish installation, I refrained from using tmutil to enable mtmfs.

Without using tmutil: with the GUI, how might a user enable local snapshots?

I wonder whether Sierra will invite the user after, say, one week or one month.

 

[KALLT]

Perhaps they did this intentionally. Snapshots produce unnecessary write operations and they might not even be used by the time the user connects to the Time Machine disk. It is a pure convenience feature.

 

[grahamperrin]

I get what you're saying but I'd not describe this type of backup as 'unnecessary' to anyone who loses data after assuming, with good reason, that Mobile Time Machine is enabled by default.

 

[KALLT]

I wouldn’t call it ‘Mobile Time Machine’. Local snapshots are auxiliary and meant to reduce the likelihood of drift and speed up actual backups. The system does not protect snapshots, it will delete them as it sees fit. Relying on them to begin with is a problem.

 

[grahamperrin]

Local snapshots are … meant to … speed up actual backups.

If I read that correctly, it's a common misunderstanding.

As far as I recall there was a very early pre-release expectation, by some testers and/or the press, that mtmfs data could/should somehow be 'fed' to more traditional Time Machine data sets. An expectation, but to the best of my knowledge (from AppleSeed and so on) it never became a reality.

Postscript

Now, I wonder whether I'm without local snapshots because my Sierra startup volume is not on an internal drive.