Automount Oddity in OS X with Spotlight metadata server (mds)

I bought a macbook air recently. This is my first mac, but I am very familiar with Unix/Linux. This is part of a series of posts on using OS X (Mountain Lion).

A Simple Thing

I have a NAS with a Samba share that I’d like to mount on the mac at a fixed location and have it to be usable by my user always. The same share might be mounted by another user on the same mac, but it can be at a different mount point. This simplifies things a bit. The mount point doesn’t have to have open permission for all users.

Using Finder

Using Finder, the first attempt is to use Go -> Connect To Server.... This automatically puts the mount as /Volumes/<sharename>. Not so bad if you have only 1 share to deal with. But if multiple users try to mount the same share, you will end up with /Volumes/<sharename>-1, /Volumes/<sharename>-2, etc. Not permanent solution.

Using Automount

Automount in OS X is pretty well documented. See man auto_master. On Linux, this is always a nice way to lazily mount a drive on demand when you visit a mapped directory. I thought this would solve my problem.

/etc/auto_master

#
# Automounter master map
#
+auto_master          # Use directory service
/net                  -hosts                -nobrowse,hidefromfinder,nosuid
/home                 auto_home             -nobrowse,hidefromfinder
/Network/Servers      -fstab
/-                    -static
/Volumes/kyle/berunda auto_mount_berunda

/etc/auto_mount_berunda

media    -fstype=smbfs    smb://downloader:v3rysekret@berunda:/&

Run sudo automount -vc and it’s good to go.

Now, when I cd into /Volumes/kyle/berunda/media, there is a slight hesitation and the share is mounted.

[~] % mount
/dev/disk0s2 on / (hfs, local, journaled)
devfs on /dev (devfs, local, nobrowse)
map -hosts on /net (autofs, nosuid, automounted, nobrowse)
map auto_home on /home (autofs, automounted, nobrowse)
map auto_mount_berunda on /Volumes/kyle/berunda (autofs, automounted, nobrowse)
//downloader@berunda/media on /Volumes/kyle/berunda/media (smbfs, nodev, nosuid, automounted, nobrowse, mounted by kal)

[~] % ls -ld /Volumes/kyle/berunda/media
drwx------  1 kal  wheel    16K Oct 14 23:23 /Volumes/kyle/berunda/media/

This was good until sometimes later. I noticed that I can’t access that directory anymore. Here is why:

[~] % sudo ls -ld /Volumes/kyle/berunda/media
drwx------  1 root  wheel  16384 Oct 14 23:23 /Volumes/kyle/berunda/media

[~] % mount
...
//downloader@berunda/media on /Volumes/kyle/berunda/media (smbfs, nodev, nosuid, automounted, nobrowse)

So whenever the mount point is unmounted – due to inactivity or manual umount, some process owned by root is accessing the location and remounting it under root. Preventing me from access it. I wonder what process could that?

[~] % sudo lsof /Volumes/kyle/berunda/media
COMMAND PID USER   FD   TYPE DEVICE SIZE/OFF NODE NAME
mds      52 root   16r   DIR  45,10    16384    2 /Volumes/kyle/berunda/media

mds is the OS X process used to index your drives and to produce the metadata that Spotlight uses to perform searches. My guess was mds traversed into the directory and automount, of course, mounted the share.

Then, I tried to add the directory to the privacy section in Spotlight.

This didn’t help. Neither did completely disabling mds using mdutil -d /. I think disabling mds using sudo launchctl unload -w /System/Library/LaunchDaemons/com.apple.metadata.mds.plist would probably work. But I am not willing to give up Spotlight completely yet.

So I need another way. Next time I will look into using launchd and SleepWatcher