Automount NFS in OS X

I work in a mixed Mac/Windows/Linux environment. The majority of our fileshares are located on Isilon gear and are accessible over SMB with AD authentication, and over NFS with LDAP authentication. Our Macs bind to AD and therefore use SMB to access fileshares. As the size of the scientific datasets people use grow, the (lack of) performance of SMB in Mac OS X becomes more of an issue — especially for people who know they can get far better performance in Windows and Linux. To remedy this, with the help of my colleague and Mac admin, Rich Trouton, we’ve started to migrate certain Mac users away from AD and SMB to LDAP and NFS. Because our Mac users have mobile accounts with local homes, the move requires a bit of finagling, which is why Rich scripted the process.

Once a Mac user’s account has been migrated to LDAP, s/he can use NFS URLs in the Finder’s Connect to Server window and will see vastly superior performance to the previous SMB connections. The more Macs we convert to LDAP/NFS, the more active connections we’ll have to our fileservers. At a certain point, this will become a problem. Fortunately, there’s a way around this that all our linux computers already use: autofs. Autofs will automatically mount fileshares on an as-needed basis and will automatically disconnect fileshares after an idle timeout period (which defaults to one hour). Another benefit of autofs is that users no longer have to mount shares manually. Simply by navigating to where the share is supposed to be will mount it there. Automount is clearly the best solution going forward.

My primary goals for this NFS automounting solution was to make it easy to manage and update — we sometimes add and remove fileshares — and to have the Macs mount fileshares at exactly the same paths as in Linux, inside a root-level directory called ‘groups’. Because of a peculiarity in OS X Lion’s Finder (that I’ll discuss later), this goal precluded the use of the automount maps that our linux hosts get from LDAP. My solution (which works with OS 10.6 through 10.8) adds entries to /etc/auto_master that reference files in a new /etc/automounts directory.

Example Scenario

Let’s say my Isilon cluster is called shares.example.com and it is exporting a number of NFS shares with root paths beginning with /ifs/groups/foo, /ifs/groups/bar, and /ifs/groups/baz. Each of these directories contains at least two subfolders which are the actual shares. I want these shares to mount inside /groups/foo, /groups/bar, and /groups/baz. To do this, I need to create three files inside a new /etc/automounts directory called foo, bar, and baz containing the respective automount maps. Because I’m working outside the user space, I’ll need root/admin privileges.

Here’s what /etc/automounts/foo looks like:

https://gist.github.com/pmbuko/9174a0542fbbe39ef3e8

The asterisk at the beginning and the ampersand at the end of the line tell automount to mount any shares it finds inside /ifs/groups/foo with the same name as the share. This saves me from having to specify each share individually. (The mount options are beyond the scope of this post, but go here if you want to learn more about them.) The other two mounts follow this same pattern. You can, of course, specify each share individually. These mount files can have any number of lines in them.

When all the mount files are written, I need to add one line per file to my /etc/auto_master file. It ends up looking like this:

https://gist.github.com/pmbuko/969461743d6e67a92f1b

Looks pretty straightforward, right? After these modifications are in place, I check to make sure all files are root:wheel owned, the automounts directory has rwxr-xr-x (755) permissions and /etc/auto_master and all files within /etc/automounts have rw-r–r– (644) permissions. Now I need to restart the automounter so it sees the new mount maps:

https://gist.github.com/pmbuko/6c360913412a65747b60

When this command runs, it should output all the new mounts it has created. The first three lines are from Apple’s default mounts:

https://gist.github.com/pmbuko/365544c3a9d1772a7e20

Now, even though it says “mounted”, nothing has actually been mounted. If you look in the Finder, you should see that autmount has created the mount  points, but nothing else. This is an important concept to understand. A share will not actually mount until you traverse its mount point. This is confusing for anyone who has not wrapped their head around autofs — and I’m staring in the general direction of most Mac users, here. For example, let’s say you want to get to /groups/foo/images. If you look inside /groups/foo in the Finder or the Terminal, you will see an empty directory. To go that next step, you’ll need to either use “Go to Folder” and specify “/groups/foo/images” or use the terminal and cd into that directory.

One last thing to mention. You will probably wish to disable the creation of .DS_Store files on network volumes when using automounts. The Finder has a bad habit of leaving these files open, so your automounted shares will not unmount after set idle times like they’re supposed to. To keep your Mac from writing .DS_Store files to network drives, run the following defaults command in the terminal. This is a per-user setting.

https://gist.github.com/pmbuko/2d84d0b9517d97d1ed99

Deploying this solution

As I mentioned earlier, because we add and remove new shares semi-regularly, I needed this solution to be manageable. If you’re already using configuration management tools in your Mac environment — be it Casper, Puppet, or anything else — you’re probably already familiar with the best way to deploy and manage a small collection of files. My colleague Rich just wrote up how to wrap all this into a package that you can deploy with your tool of choice. Any time we add or remove a share, we can push out a new package with the changes and the packages postinstall script will reload automount. The reload process won’t affect any active mounts so we can push the package out at any time.

Appendix: Why not use LDAP?

Because the Finder (at least since 10.7) will rename mount points to match the filename that contains the autofs mapping. Our LDAP server’s maps are named with a format of auto.groups.foo. As soon as you go into a share inside /groups/foo, e.g. /groups/foo/images, the Finder renames the foo directory to auto.groups.foo. Directory names viewed from the Terminal are unaffected.