Archive for May 7th, 2012

Ubuntu 12.04: NFS Mounts vs. Upstart

Back in the old days, the Unix startup sequence was rigidly fixed. For a variety of reasons, that’s no longer the case; Ubuntu (and, presumably, other distros) now use upstart, which turns the startup sequence into a lightly documented Pachinko machine. This parallel processing presumably works great for most of Ubuntu’s use cases and falls flat on its face for me: I’m apparently the only person who expects NFS mounts to be in place before signing in.

Well, maybe other folks expect that, but the entire startup mechanism is apparently broken as designed.

The only solution seems to be stalling the user sign-on screen by jamming the display manager until the NFS client hauls itself to its feet. This takes up to a minute, for reasons I do not understand, but it’s better to let it run to completion rather than signing on and expecting one’s files to be in the right places. Email clients, in particular, have difficulty coping with missing files.

The fix involves adding a line to /etc/init/lightdm.conf, as mentioned there (albeit with incorrect syntax):

start on ((filesystem
           and runlevel [!06]
           and started dbus
           and (drm-device-added card0 PRIMARY_DEVICE_FOR_DISPLAY=1
                or stopped udev-fallback-graphics)
           and mounted MOUNTPOINT=/mnt/bulkdata)
          or runlevel PREVLEVEL=S)

I tried to check for another filesystem that should also be mounted, but, as I understand neither the syntax nor the semantics of the language, what you see is what finally worked. As it turns out, upstart's syntax error messages aren’t particularly helpful; a single line (helpfully relating, perhaps, that the parser expected a token on line 16) appears on VT 7, but if you don’t know to switch from VT 1, you’ll never get even that minimal assistance. No, such errors don’t appear in the /var/log/upstart/* logs.

For unknown reasons, waiting for the remote-filesystems event didn’t delay the startup at all. Evidently, mountall emits that event almost immediately, long before the NFS mounts happen. Perhaps the event occurs even when the mount fails, contrary to what the doc suggests?

Most of the debugging occurred through an ssh session across the room. Edit the file, try a new version, reboot, watch for the filesystems to come up, watch for the sign-in screen to appear. Or not, as the case may be.

Grumpy though I may seem, the great thing about Open Source / Free Software is that when it breaks, you have access to all the pieces and can actually fix the problem. That makes up for nearly everything, I’d say.

No, I didn’t update any of those bug reports or start another one. It’s obvious this isn’t getting any attention, so what’s the point? If you’re also having the problem, you’ll eventually wind up here…

FWIW, I knew the NFS mounts weren’t working because I always set the screen background to an image on the file server: no mount = no picture = fix-the-problem-now. This image seemed appropriate:

XB-70A Cockpit

XB-70A Cockpit

Back then, transistors were countable resources…

[Update: The previous picture link, now broken, was to http://www.nasaimages.org/luna/servlet/detail/nasaNAS~2~2~2995~104520. The revised link points to a description on archive.org, with versions of the picture available for download.]

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