Autofs and a couple tricks with NFS shares

Autofs is great especially for NFS mounts between systems.  Autofs will mount file systems on demand and then un-mount them again when they are not needed.  This is especially a nice trick where servers are sharing NFS shares compared to putting the shares in fstab which mounts the file system on boot potentially putting you in a deadlock where server A is waiting on a share from server B and server B is waiting on a share from server A... A common issue for example is mounting /home from a shared location but then no other server can boot until the home file server is up and deadlocks are bad, um 'kay?

"yum install autofs" as needed, use your package manager of choice.  Once you fire up the automount daemon, you can poke around in the configuration.

First thing you'll want to try with is in auto.master enabling the net (or nfs) -hosts line.  This will create a multi-mount in /net where you can access shares via /net/<hostname>/<share path>.

That's really it.  You can directly access files, for example in /net/homefs/data/home/username.  Automount will automatically mount that share when it is accessed and remove it after it's been left idle.

What's it doing?

First, it will look up shares for you.  When you do `ls /net/hostname`, it will return a list of shares available from the server "hostname".  It's really that easy.

Any access to a share is automatically mounted.  A shared folder, call it "work", will be mounted on the first user request for a file from that share.  Whether that's someone using 'ls' or else writing a file to a specified path.

For convenience, my first tip is that you use symlinks to point to specific shares or locations.  Rather than using the path "/net/workfs/export/work", do something like `ln -s /net/workfs/export/work $HOME/work`.   Another example is for shared home directories, super common in UNIX environments.  So link /home to /net/<server>/path/to/shared/home.  It will bring up the shared home directories when a user tries to logon and will unmount the home share after the users are logged out.

This brings me to my next tip: the automatic timeout.  Autofs will un-mount the share after an idle period.  10 minutes by default (depending on your platform).  This may cause you some grief, for example if you have a job that runs every 10 minutes.  You should adjust this timeout based on your needs (either up or down) but unless your running something on a schedule every 10 minutes, you probably won't have much of a problem with this default.

You can also tune your NFS settings in your auto.master config file.  The defaults should work for most systems but if you do have to do NFS tuning, you can do this with autofs either for all NFS mounts or you can create specific mounts as needed.

The interesting thing with autofs is you don't have to use it just for network shares.  You can use it for regular devices as well.  One of the main things is that again, anything in automount will be mounted on demand and not at boot time.  So if you have a large data volume, you can add it specifically to the auto.misc file instead of fstab.

From time to time autofs can get a bit mucked up.  Usually when "you screw around too much".  If stopping autofs and umounting any left-over shares doesn't work, remember "umount -f -l" which is force lazy unmount.  Very useful.  If the folders don't go away, like /net/server/path/to/share, try doing umount on them and then you can remove them (rm -Rf), just be careful.  It depends whether rebooting is more risky than an rm -Rf.