This should help. kern.log: Jul 2 05:41:32 server1 kernel: [136565.201601] device vethbJ4JsM left promiscuous mode Jul 2 05:41:32 server1 kernel: [136565.201603] vmbr: port 5(vethbJ4JsM) entered disabled state Jul 2 05:41:38 server1 kernel: [136570.551496] vmbr: port 2(veth49SiBX) entered forwarding state Jul 2 05:41:38 server1 kernel: [136570.971787] device vethgEUinJ entered promiscuous mode Jul 2 05:41:38 server1 kernel: [136570.971858] IPv6: ADDRCONF(NETDEV_UP): vethgEUinJ: link is not ready Jul 2 05:41:39 server1 kernel: [136571.574489] vmbr: port 3(vethdl0Frj) entered forwarding state Jul 2 05:41:42 server1 kernel: [136575.242996] unregister_netdevice: waiting for lo to become free. Usage count = 1 Jul 2 05:41:42 server1 kernel: [136575.282886] vmbr: port 4(vethwdXg5p) entered forwarding state Jul 2 05:41:44 server1 kernel: [136576.945295] vmbr: port 6(vethxUZwwG) entered forwarding state Jul 2 05:41:47 server1 kernel: [136580.142190] vmbr: port 7(vethpuofJs) entered forwarding state Jul 2 05:41:53 server1 kernel: [136585.473065] unregister_netdevice: waiting for lo to become free. Usage count = 1 Jul 2 05:42:03 server1 kernel: [136595.703141] unregister_netdevice: waiting for lo to become free. Usage count = 1 Jul 2 05:42:13 server1 kernel: [136605.933214] unregister_netdevice: waiting for lo to become free. Usage count = 1 Jul 2 05:42:23 server1 kernel: [136616.163283] unregister_netdevice: waiting for lo to become free. Usage count = 1 Jul 2 05:42:33 server1 kernel: [136626.237470] unregister_netdevice: waiting for lo to become free. Usage count = 1 Jul 2 05:42:34 server1 kernel: [136627.221675] device vethkKcWdk entered promiscuous mode Jul 2 05:42:34 server1 kernel: [136627.221727] IPv6: ADDRCONF(NETDEV_UP): vethkKcWdk: link is not ready Jul 2 05:42:38 server1 kernel: [136630.800271] device veth5guMb3 entered promiscuous mode Jul 2 05:42:38 server1 kernel: [136630.800341] IPv6: ADDRCONF(NETDEV_UP): veth5guMb3: link is not ready Jul 2 05:42:44 server1 kernel: [136636.471570] unregister_netdevice: waiting for lo to become free. Usage count = 1 Jul 2 05:42:54 server1 kernel: [136646.701652] unregister_netdevice: waiting for lo to become free. Usage count = 1 Jul 2 05:43:04 server1 kernel: [136656.931720] unregister_netdevice: waiting for lo to become free. Usage count = 1 Jul 2 05:43:14 server1 kernel: [136667.161755] unregister_netdevice: waiting for lo to become free. Usage count = 1 Jul 2 05:43:25 server1 kernel: [136677.391864] unregister_netdevice: waiting for lo to become free. Usage count = 1 Jul 2 05:43:34 server1 kernel: [136686.721504] device vethOk6Soj entered promiscuous mode Jul 2 05:43:34 server1 kernel: [136686.721584] IPv6: ADDRCONF(NETDEV_UP): vethOk6Soj: link is not ready Jul 2 05:43:35 server1 kernel: [136687.621938] unregister_netdevice: waiting for lo to become free. Usage count = 1 Jul 2 05:43:38 server1 kernel: [136690.857458] device vethjxu2iI entered promiscuous mode Jul 2 05:43:38 server1 kernel: [136690.857565] IPv6: ADDRCONF(NETDEV_UP): vethjxu2iI: link is not ready Jul 2 05:43:45 server1 kernel: [136697.852009] unregister_netdevice: waiting for lo to become free. Usage count = 1 Jul 2 05:43:55 server1 kernel: [136708.082040] unregister_netdevice: waiting for lo to become free. Usage count = 1 Jul 2 05:44:05 server1 kernel: [136718.312155] unregister_netdevice: waiting for lo to become free. Usage count = 1 Jul 2 05:44:16 server1 kernel: [136728.542232] unregister_netdevice: waiting for lo to become free. Usage count = 1 Jul 2 05:44:26 server1 kernel: [136738.772298] unregister_netdevice: waiting for lo to become free. Usage count = 1 Jul 2 05:44:34 server1 kernel: [136746.713370] device vethxTRBXO entered promiscuous mode Jul 2 05:44:34 server1 kernel: [136746.713442] IPv6: ADDRCONF(NETDEV_UP): vethxTRBXO: link is not ready Jul 2 05:44:36 server1 kernel: [136749.002369] unregister_netdevice: waiting for lo to become free. Usage count = 1 Jul 2 05:44:38 server1 kernel: [136750.845172] device veth1ILXYc entered promiscuous mode Jul 2 05:44:38 server1 kernel: [136750.845262] IPv6: ADDRCONF(NETDEV_UP): veth1ILXYc: link is not ready Jul 2 05:44:46 server1 kernel: [136759.236438] unregister_netdevice: waiting for lo to become free. Usage count = 1 Jul 2 05:44:57 server1 kernel: [136769.466512] unregister_netdevice: waiting for lo to become free. Usage count = 1 Jul 2 05:45:07 server1 kernel: [136779.696578] unregister_netdevice: waiting for lo to become free. Usage count = 1 Jul 2 05:45:15 server1 kernel: [136787.680886] INFO: task lxc-start:27612 blocked for more than 120 seconds. Jul 2 05:45:15 server1 kernel: [136787.680925] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. Jul 2 05:45:15 server1 kernel: [136787.680962] lxc-start D ffff88041ecd3f40 0 27612 19646 0x00000000 Jul 2 05:45:15 server1 kernel: [136787.680967] ffff88010bd57d20 0000000000000082 ffff8801113b8000 ffff88010bd57fd8 Jul 2 05:45:15 server1 kernel: [136787.680972] ffff88010bd57fd8 ffff88010bd57fd8 ffff8804085645c0 ffff8801113b8000 Jul 2 05:45:15 server1 kernel: [136787.680975] ffffffff81cbbd60 ffff8801113b8000 ffffffff81cbbd64 00000000ffffffff Jul 2 05:45:15 server1 kernel: [136787.680979] Call Trace: Jul 2 05:45:15 server1 kernel: [136787.680989] [] schedule+0x29/0x70 Jul 2 05:45:15 server1 kernel: [136787.680993] [] schedule_preempt_disabled+0xe/0x10 Jul 2 05:45:15 server1 kernel: [136787.680997] [] __mutex_lock_slowpath+0xd7/0x150 Jul 2 05:45:15 server1 kernel: [136787.681001] [] mutex_lock+0x2a/0x50 Jul 2 05:45:15 server1 kernel: [136787.681006] [] copy_net_ns+0x84/0x110 Jul 2 05:45:15 server1 kernel: [136787.681011] [] create_new_namespaces+0x101/0x1b0 Jul 2 05:45:15 server1 kernel: [136787.681015] [] copy_namespaces+0xa3/0xe0 Jul 2 05:45:15 server1 kernel: [136787.681020] [] copy_process.part.22+0x939/0x1510 Jul 2 05:45:15 server1 kernel: [136787.681025] [] do_fork+0xa9/0x360 Jul 2 05:45:15 server1 kernel: [136787.681029] [] sys_clone+0x16/0x20 Jul 2 05:45:15 server1 kernel: [136787.681032] [] stub_clone+0x69/0x90 Jul 2 05:45:15 server1 kernel: [136787.681037] [] ? system_call_fastpath+0x1a/0x1f See also: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1021471 https://bugs.launchpad.net/ubuntu/+source/lxc/+bug/1039196