Upstart vs. NFS Mounts vs. Display Manager: Resolved!

Quick summary: the current Linux startup machinery Runs All The Things! in parallel, leaving you to figure out all the interdependencies and update all the script files to match your requirements. Mostly, the distro maintainers figure all that, but if you have essential files mounted as NFS shares, then you can will reach a login screen before the mount process completes.

Having wrestled with this problem for a while, I think I’ve doped out the right way to coerce the Upstart Pachinko Machine to converge on a workable login.

The solution is to fire off a unique signal after the NFS mount command, then force the display manager to wait until it receives that signal, rather than depend on happenstance as I did before. The mounts occur in /etc/init/local.conf, which now looks like this:

description "Stuff that should be in /etc/rc.local"
author "Ed Nisley - KE4ZNU"

start on (local-filesystems and net-device-up IFACE=em1)
stop on shutdown

emits nfs-mounted

script

logger Starting local init...

logger Mounting NFS filesystems
mount /mnt/bulkdata
mount /mnt/userfiles
mount /mnt/diskimages
mount /mnt/music
initctl emit nfs-mounted
logger Ending local init

end script

The start condition ensures that this code won’t run until the wired LAN is up; note that what was once eth0 is now em1. Then, after the mounts happen, initctl fires the nfs-mounted signal.

The modification to /etc/init/lightdm.conf script consists of one additional line to wait for that signal:

start on ((filesystem
           and runlevel [!06]
           and started dbus
           and plymouth-ready
           and nfs-mounted)
          or runlevel PREVLEVEL=S)

stop on runlevel [016]

emits login-session-start
emits desktop-session-start
emits desktop-shutdown

I’m not convinced lightdm.conf is the right spot to jam a stick in the gears, but it seems to be the least-awful alternative. The login-session-start signal doesn’t appear in any file in that subdirectory and I have no idea where else to look.

Anyhow, the greeter screen now shows a desktop background from the NFS mount, which I regard as A Good Sign:

Until the next startup revision, anyway…