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Created November 19, 2018 17:17
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Use autofs on Mac OS X to mount network shares automatically during access

Autofs on Mac OS X

With autofs you can easily mount network volumes upon first access to the folder where you want to mount the volume. Autofs is available for many OS and is preinstalled on Mac OS X so I show you how I mounted my iTunes library folder using this method.

Prepare autofs to use a separate configuration file

autofs needs to be configured so that it knows where to gets its configuration. Edit the file '/etc/auto_master' and add the last line:

# Automounter master map
+auto_master		# Use directory service
/net			-hosts		-nobrowse,hidefromfinder,nosuid
/home			auto_home	-nobrowse,hidefromfinder
/Network/Servers	-fstab
/-			-static
/-          auto_smb    -nosuid,noowners
#/-			auto_afp	-nobrowse,nosuid

This will tell autofs to look for a file in the '/etc' folder with name 'auto_smb'. In this case I want to create a configuration for automatically mount SMB volumes. You are free to choose a different name and can also use afp/cifs/nfs etc.

Content of the configuration file

Normally Mac OS X tries to mount network shares into the '/Volumes' folder. This is the default folder for all mounted shares on a mac. However, if you try to directly mount into this folder, autofs will fail. You just add a '/../' in front of your desired mount path and Mac OS X will even accept the Volumes folder. However, some Mac OS Version doesn't like this so I switched over to use my own folder named '/mount'.

If you want to configure AFP, do it like this:

So add this line to '/etc/auto_afp':

/../Volumes/music	-fstype=afp,rw afp://ip-address:/music

Mac OS X is clever enough to lookup the username and password from the Mac keychain so there's no need to add the username and password in clear text to the configuration file.

If you want to configure SMB, do it like this:

Add this line to '/etc/auto_smb':

/mount/music    -fstype=smbfs,soft,noowners,nosuid,rw ://username:password@ip-address:/music

Unfortunately you will need to add the user and password to the resource :( You can try to lock it down further using the Mac OS permissions but that won't help when the attackers user got admin rights as well.

Access the folder and see autofs in action

You now need to restart the autofs service with the command 'sudo automount -cv'. If you now type mount, you'll see a listing of currently mounted volumes. Your desired volume shouldn't be mounted, so unmount it with 'sudo umount /Volumes/volumename' or 'sudo umount /mount/music' before we continue.

You can now switch to '/Volumes/music' or '/mount/music' folder or let it list on the terminal. Once you do that autofs will automatically try to mount the desired volume into this folder.

See an example and explanation in action

Visit my blog post where I explain this gist a little bit more in detail.

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