We had a customer email in after updating to Jaunty recently. They said the following
Hi guys, I upgraded my VPS a little while back to Ubuntu Jaunty (because I was several versions out of date and the apt repositories had gone away.) I never actually rebooted the machine afterwards though because it wasn't a good time to potentially interrupt email. I finally got around to doing that, and the VPS won't come back onto the network. Logging in over the console, it looks like there are no network interfaces configured. A few other things don't feel right (eg, dmesg tells me that the current tls library or perhaps libc isn't xen-friendly.) but mostly everything *looks* like it's ok but doesn't have a network interface.. services that want to resolve hostnames didn't start up, etc. Trying to dig into the problem, it looks like there are no modules installed for the kernel, but this is where my expertise runs out.. I don't know enough about Xen to know if everything was just precompiled into the kernel, or if I blew away my kernel modules during upgrade.
I was curious so logged in via the console (you can do this yourself by setting a password or adding your ssh key at http://rimuhosting.com/cp/console.jsp ).
I ran ifup and got the following errors
root@charon ~ # ifup eth0
ifup: failed to open statefile /var/run/network/ifstate: No such file or directory
so i checked and /var/run/network did not exist. I fixed this
root@charon network # mkdir /var/run/network/
root@charon network # ifup eth0
* if-up.d/mountnfs[eth0]: waiting for interface lo before doing NFS mounts
root@charon network # ifconfig
eth0 Link encap:Ethernet HWaddr aa:00:d6:a1:5e:e4
inet addr:18.104.22.168 Bcast:22.214.171.124 Mask:255.255.255.128
inet6 addr: fe80::a800:d6ff:fea1:5ee4/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:56 errors:0 dropped:0 overruns:0 frame:0
TX packets:15 errors:0 dropped:0 overruns:0 carrier:0
RX bytes:5447 (5.4 KB) TX bytes:1074 (1.0 KB)
The file system on Ubuntu in /var/run is a virtual filesystem on Ubuntu, I googled and came across this post here https://bugs.launchpad.net/ubuntu/+bug/367171 which clearly logs the bug, and a fix.
The fix i applied which was adding the following into /etc/init.d/networking
[ -d /var/run/network ] || mkdir -p /var/run/network
This checks if the dir exists and creates it if it doesn't.
This does fix the problem but its a bit of a hack. I noticed a link later on down the post which took me to https://bugs.launchpad.net/ubuntu/+bug/377432 . This link had a bit more technical information. They said look for the following files and remove them.