Automounting NFS share in OS X into /Volumes

osx_automount_nfs.md

I have spent quite a bit of time figuring out automounts of NFS shares in OS X...

Somewhere along the line, Apple decided allowing mounts directly into /Volumes should not be possible:

/etc/auto_master (see 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_nfs	-nobrowse,nosuid

/etc/auto_nfs (this is all one line):

/Volumes/my_mount    -fstype=nfs,noowners,nolockd,noresvport,hard,bg,intr,rw,tcp,nfc nfs://192.168.1.1:/exports/my_share

Make sure you:

sudo chmod 644 /etc/auto_nfs

Otherwise the automounter will not be able to read the config and fail with a ... parse_entry: getmapent for map failed... error in /var/log/messages

This will not work (anymore!) though it "should".

$ sudo automount -cv
...
automount: /Volumes/my_mount: mountpoint unavailable

Note that, if you manually create the mount point using mkdir, it will mount. But, upon restart, OS X removes the mount point, and automounting will fail.

What's the solution?

It's so easy my jaw dropped when I figured it out. Basically, we trick OS X into thinking we're mounting somewhere else.

When you're talking about paths in just about any environment, the root folder is the highest path you can reach, whether it's C:\ (windows) or / (*nix)

When you're at this path, attempting to reach the parent path, via .. will keep you at the root path.

For example: /../../../../ is still just /

By now, a few of you have already figured it out.

TL;DR / Solution:

Change your /etc/auto_nfs config from (this is all one line):

/Volumes/my_mount    -fstype=nfs,noowners,nolockd,noresvport,hard,bg,intr,rw,tcp,nfc nfs://192.168.1.1:/exports/my_share

For pre-Catalina: To (this is all one line)

/../Volumes/my_mount    -fstype=nfs,noowners,nolockd,noresvport,hard,bg,intr,rw,tcp,nfc nfs://192.168.1.1:/exports/my_share

For Catalina and up: To (this is all one line)

/System/Volumes/Data/../Data/Volumes/my_mount    -fstype=nfs,noowners,nolockd,noresvport,hard,bg,intr,rw,tcp,nfc nfs://192.168.1.1:/exports/my_share

And re-run the automounter:

$ sudo automount -cv
...
automount: /Volumes/my_mount: mounted

..... there you go! Technically /../Volumes is still /Volumes, but the automounter does not see things that way ;)

This configuration persists the mount across restarts, and creates the mountpoint automatically.

I KNOW, RIGHT?

Feel free to send me large checks and/or high five the screen. [email protected]

This comment belongs in the "FWIW" column, but this is something I feel all users of anything that touches autofs should know:

During any OS update or upgrade, Apple routinely replaces the file /etc/auto_master with their "DEFAULT" version; i.e. they replace/over-write any and all changes you might have made to this file (and perhaps others). They do this without warning or notification.

Whether Apple's behavior here is mean-spirited (Apple are assholes), absent-minded ("Oh!... I forgot that function/routine was still in the upgrade script !"), or well-intentioned (some undisclosed security issue with autofs?) I cannot say - and apparently Apple will not say. But in any event, Apple's behavior is most certainly annoying!

But - what are the solutions? I use two:

1. Once you have a working, modified /etc/auto_master file, make a backup (e.g. /etc/auto_master.backup), and designate this backup as immutable (i.e. sudo chflags schg /etc/auto_synology.backup).
2. Create a launchd job (I use LaunchControl for this) to check the MD5 signature of /etc/auto_master routinely and periodically for shanges, and issue a notification if it finds the file has been changed.