Preventing Shutdown on Active NFS Servers?

Ed Almos asks: "Like many Slashdot Readers, I run a small network at home with a server and a number of desktops. The server holds all our files as NFS shares and doubles as a desktop machine should the need arise. Problems however occur if the server is shut down whilst there are NFS shares in use, the minimum disruption is a crashed desktop and a couple of times I have had to deal with corrupted files. Does anyone know of a way to prevent shutdown of a machine if someone else has drives mounted to its NFS shares ? I have already explored use of the /etc/shutdown.allow file but all this does is determine who can kill the machine. The minimal solution would be something similar to a Microsoft Windows system, where a request to shutdown brings up a warning window that there are users connected to the system, but I am not sure how to achieve this on a Linux system. Ideally I would like to prevent shutdown of a system with active NFS shares altogether, or at least until the user has unmounted and logged off the network."

Comments

You've got something wrong...

[Whip]

If your NFS server rebooting, shutting down, or crashing causes any problem but temporarilly 'hung' clients, you have something wrong.

NFS is explicitly designed to be stateless, precisely to allow it to function across server reboots, crashes, and other fun. If your clients are crashing, or getting back corrupted data, something is screwed up somewhere.

And, by the way, if you're getting corrupted data on a server crash, and the server is linux, you just had an object lesson on why it's bad that linux NFS defaults to async writes. :)

Yeah, but the client thinks it's stateful

[bill_mcgonigle]

put a program on each client machine, call it nfsmounts and it would go a little something like this:

mount | grep $1 | wc -l

then write a wrapper on the server that does

foreach client (client list)
mounted = ssh client nfsounts `hostname`
ok = false if (mounted)
end

you can hook that into your shutdown script, and abort if there are any clients who think they have a mounted drive.

of course, read the other suggestions about mount options. Noone's mentioned sync yet, but don't mount your shares async even though the performance is so much better or you'll loose data.