I enjoy NFS since many years. But, with laptops, by essence that are not always connected to the same local netwok, it’s quite a pain in the ass.
Editing /etc/fstab each time you connect is not really an option. AutoFS seemed a great idea. It took me a while to get the damn thing running and it failed to work after a reboot. After spending plenty of time googling around, fooling around, I eventually reached the conclusion that I was not able to set it up in a reliable fashion. So I dropped the idea.
Then I had some hopes in regard of the DHCP client. It provides hooks, with plenty of variables useful to determine to which network you are connected to. I gave it a try. Worked well: a script in dhclient-exit-hooks.d to mount NFS shares after the interface is brought up on the LAN, the counterpart in dhclient-enter-hooks.d to umount NFS shares just before the interface is going down.
Then I realized that one of the two laptops supposed to make use of this script is running Ubuntu -not mine. And Ubuntu use by default a very very nasty software called NetworkManager, the kind of well thought user interface that stores configuration in anything but the standard stuff that worked finely before it even existed. Yeah, it literally makes a litter of /etc/network/interface. So, no, obviously, handling properly /etc/dhcp/dhclient-*-hooks.d/ scripts is not an option for NetworkManager, it’s so much better to reinvent the wheel with a poorly designed (And What’s The Deal With These Upper Cases?) /etc/NetworkManager/dispatcher.d.
Plenty of people complained already about obvious limits of NetworkManager. Sure, there’s is room for improvements and it’s better to contribute than just to rant. But considering the kind of replies provided to NetworkManager people about bugs reports (cause, really, not handling dhcp-*-hooks.d is a regression), I think I’ll pass. Funny links though: “After discussing with a few folks we found that pre-up will not come back … please provide detailed infos for your use-case as we have to find other means to achieve this.” (hum, they… found that useful working features will not come back but havent found any better alternative yet ?), “if the resolvconf abilities are not enough you can also stuff in a NM dispatcher.d script (see: /etc/NetworkManager/dispatcher.d/)” (please, have fun writing new scripts to replace the ones that worked just fine). In fact, when developers deal with such issue like this “Changed in network-manager (Fedora): status: Confirmed → Won’t Fix”, best is just to find a workaround that absolutely not relies on their stuff that is sure to be broken some other day – no doubt that if a new trend comes, they’ll ask you to one more time rewrite scripts just to do the same frickin thing you were able to do years ago with simple dhclient-*-hooks.d.
So I finally came up with /etc/network/if-up.d and /etc/network/if-down.d scripts. Its quite standard and, oh!, NetworkManager got a “dispatcher” that run-parts on this dir. The obvious drawback is the fact it cannot be used to properly unmount the NFS shares because it’s unclear whether NetworkManager will run if-down.d before or after having brought down the network interface and, also, because it’s way to more painy to determine whether the loss of the current interface means loosing the relevant network where shares are (if you loose the Wifi, clearly, you may still be properly connected to the LAN). And I’m off trying to guess how behave and how will behave in 6 month this piece of software.
Instead of hardcoding the list of NFS shares in one more script, considering that initscripts already provides a well-thought /etc/network/if-up.d/mountnfs, I figured I would simply rely on /etc/fstab. My /etc/network/if-up.d/01prepmountnfs (that must run before initscript’s mountnfs) simply goes through /etc/fstab, looks for NFS shares that are in noauto mode (so, not configured to be mounted automatically when the box starts), find out if the server exists on the current LAN. If so, it removes the noauto option and then initscript’s mountnfs does its magic. On Ubuntu, there’s no /etc/network/if-up.d/mountnfs, but the following is enough to replace it:
mount -a" > /etc/network/if-up.d/mountnfs
chmod a+x /etc/network/if-up.d/mountnfs
The /etc/network/if-down.d/unprepmountnfs counterpart only reverts /etc/fstab to its previous state. Yes, if you loose connection to the NFS server, your X session will probably get frozen. For the reasons previously stated, for now it will have to do.