为什么不启动libvirt“用户模式networking”？

运行Ubuntu 16.04，默认情况下，默认的virbr0界面在启动时并不是默认启动的，这意味着我必须使用命令手动启动它，

$ sudo virsh net-start default 

也许没有什么大不了的，我知道如何解决这个问题，但是下面的命令的输出表明virbr0被configuration为自动启动：

 $ virsh net-list --all Name State Autostart Persistent ---------------------------------------------------------- default active yes yes 

有没有人有任何指望，看看旁边帮助debugging？

更新：

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在启动后在/ var / log / syslog中看到的一些选定的行不帮助我，但可能对某人有意义：

 systemd-udevd[368]: Could not generate persistent MAC address for virbr0: No such file or directory NetworkManager[862]: <info> [1508409794.6955] device added (path: /sys/devices/virtual/net/virbr0, iface: virbr0): no ifupdown configuration found. NetworkManager[862]: <info> [1508409794.6956] device added (path: /sys/devices/virtual/net/virbr0-nic, iface: virbr0-nic): no ifupdown configuration found. NetworkManager[862]: <info> [1508409794.7711] device (virbr0-nic): state change: unmanaged -> unavailable (reason 'connection-assumed') [10 20 41] NetworkManager[862]: <info> [1508409794.7725] device (virbr0-nic): state change: unavailable -> disconnected (reason 'none') [20 30 0] NetworkManager[862]: <info> [1508409796.0723] device (virbr0): state change: unmanaged -> unavailable (reason 'connection-assumed') [10 20 41] avahi-daemon[847]: Registering new address record for 192.168.122.1 on virbr0.IPv4. NetworkManager[862]: <info> [1508409796.0734] device (virbr0): state change: unavailable -> disconnected (reason 'connection-assumed') [20 30 41] NetworkManager[862]: <info> [1508409796.0739] device (virbr0): Activation: starting connection 'virbr0' (6a02deba-6a45-44f3-8c7d-92bb6f8c287b) . . . NetworkManager[862]: <info> [1508409796.0829] device (virbr0): Activation: successful, device activated. NetworkManager[862]: <info> [1508409796.0833] device (virbr0-nic): state change: secondaries -> activated (reason 'none') [90 100 0] nm-dispatcher: req:5 'up' [virbr0]: new request (2 scripts) nm-dispatcher: req:5 'up' [virbr0]: start running ordered scripts... NetworkManager[862]: <info> [1508409796.0877] device (virbr0-nic): Activation: successful, device activated. nm-dispatcher: req:6 'up' [virbr0-nic]: new request (2 scripts) nm-dispatcher: req:6 'up' [virbr0-nic]: start running ordered scripts... avahi-daemon[847]: Interface virbr0.IPv4 no longer relevant for mDNS. avahi-daemon[847]: Leaving mDNS multicast group on interface virbr0.IPv4 with address 192.168.122.1. kernel: [ 11.827450] virbr0: port 1(virbr0-nic) entered disabled state NetworkManager[862]: <info> [1508409796.4151] device (virbr0): state change: activated -> unmanaged (reason 'connection-assumed') [100 10 41] avahi-daemon[847]: Withdrawing address record for 192.168.122.1 on virbr0. nm-dispatcher: req:7 'down' [virbr0]: new request (2 scripts) nm-dispatcher: req:7 'down' [virbr0]: start running ordered scripts... kernel: [ 13.245387] device virbr0-nic left promiscuous mode kernel: [ 13.245390] virbr0: port 1(virbr0-nic) entered disabled state NetworkManager[862]: <info> [1508409797.8565] device (virbr0-nic): state change: activated -> unmanaged (reason 'unmanaged') [100 10 3] NetworkManager[862]: <info> [1508409797.8565] device (virbr0): bridge port virbr0-nic was detached NetworkManager[862]: <info> [1508409797.8566] device (virbr0-nic): released from master device virbr0 NetworkManager[862]: <info> [1508409797.8620] devices removed (path: /sys/devices/virtual/net/virbr0-nic, iface: virbr0-nic) nm-dispatcher: req:8 'down' [virbr0-nic]: new request (2 scripts) nm-dispatcher: req:8 'down' [virbr0-nic]: start running ordered scripts... NetworkManager[862]: <info> [1508409797.8990] devices removed (path: /sys/devices/virtual/net/virbr0, iface: virbr0) 

看起来有点像virbr0被启用，然后在启动时再次被禁用。