Just managed to reproduce it here, it's caused by Network Manager deciding to mess with our bridge instead of leaving it alone as it should.
Current workarounds include: - reboot - systemctl stop network-manager && systemctl restart lxc-net && systemct start network-manager This only kicks in when the interface is brought up after network- manager, so it doesn't affect boot since lxc-net starts before network- manager and it doesn't affect upgrades where a container is already running (as we don't destroy the bridge in that case). But it does absolutely affect all new installs and upgrades done when no container is running. This is a critical regression in Network Manager behavior, NM should NEVER touch non-physical interfaces and it should even less start flushing existing network configuration. Changes are this affects libvirt too, unless libvirt bring up takes long enough to win the race against NM. ** Package changed: lxc (Ubuntu) => network-manager (Ubuntu) ** Changed in: network-manager (Ubuntu) Importance: Undecided => Critical ** Changed in: network-manager (Ubuntu) Status: New => Triaged ** Also affects: network-manager (Ubuntu Xenial) Importance: Critical Status: Triaged ** Also affects: network-manager (Ubuntu Wily) Importance: Undecided Status: New ** Changed in: network-manager (Ubuntu Wily) Status: New => Triaged ** Changed in: network-manager (Ubuntu Wily) Importance: Undecided => Critical ** Tags added: regression-release -- You received this bug notification because you are a member of Ubuntu Touch seeded packages, which is subscribed to lxc in Ubuntu. https://bugs.launchpad.net/bugs/1512749 Title: lxcbr0 dissappears on Ubuntu 15.10 Status in network-manager package in Ubuntu: Triaged Status in network-manager source package in Wily: Triaged Status in network-manager source package in Xenial: Triaged Bug description: After initial upgrade from Ubuntu 15.04 to Ubuntu 15.10 LXC worked for a couple days then failed. I found that the lxcbr0 interface no longer existed. I reported this on the lxc-user alias and about the same time several others had this happen to them also. Serge Hallyn requested I open a launchpad bug and post some info but before I could gather that info the system returned to normal (re lxcbr0 was back) the next day after the server was booted up again. note: at least one other person had this happen to them also (lxcbr0 came back by itself). Today, I booted this server again and ... again lxcbr0 was missing where it had been working last night. Below is all of the Info Serge Hallyn asked me to post. $ ifconfig lxcbr0 lxcbr0: error fetching interface information: Device not found $ journalctl -u lxc-net -- Logs begin at Tue 2015-11-03 07:25:22 EST, end at Tue 2015-11-03 10:02:08 EST Nov 03 07:25:48 server3 systemd[1]: Starting LXC network bridge setup... Nov 03 07:25:50 server3 lxc-net[913]: dnsmasq: failed to create listening socket Nov 03 07:25:50 server3 lxc-net[913]: Failed to setup lxc-net. Nov 03 07:25:50 server3 systemd[1]: Started LXC network bridge setup. root@server3:/home/bmullan# /usr/lib/x86_64-linux-gnu/lxc/lxc-net stop # note - execution just returns to command line root@server3:/home/bmullan# >> and lxcbr0 is still missing # ifconfig lxcbr0 lxcbr0: error fetching interface information: Device not found root@server3:/home/bmullan# /usr/lib/x86_64-linux-gnu/lxc/lxc-net start dnsmasq: failed to create listening socket for 10.0.3.1: Cannot assign requested address Failed to setup lxc-net. root@server3:/home/bmullan# $ uname -a Linux server3 4.2.0-16-generic #19-Ubuntu SMP Thu Oct 8 15:35:06 UTC 2015 x86_64 x86_64 x86_64 GNU/Linux $ lsb_release -a No LSB modules are available. Distributor ID: Ubuntu Description: Ubuntu 15.10 Release: 15.10 Codename: wily To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/network-manager/+bug/1512749/+subscriptions -- Mailing list: https://launchpad.net/~touch-packages Post to : touch-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~touch-packages More help : https://help.launchpad.net/ListHelp