在命令行启动KVM虚拟机时报错：启动失败，找不到 default 网络
[root@localhost ~]# virsh start centos7.0
error: Failed to start domain centos7.0
error: Network not found: no network with matching name 'default'
但是此前是有default网络的，过了一夜重新开机后再启动就报错了。首先查找一下default.xml 的存放路径，
[root@localhost ~]# find / -name "default.xml"
/run/libvirt/storage/default.xml
/etc/libvirt/storage/default.xml
/etc/libvirt/storage/autostart/default.xml
/usr/share/backgrounds/default.xml
/usr/share/libvirt/networks/default.xml
可以看出有很多 xml ，选择与network和libvirt有关的进行执行
[root@localhost ~]# virsh net-define /usr/share/libvirt/networks/default.xml
Network default defined from /usr/share/libvirt/networks/default.xml
[root@localhost ~]# virsh net-start default
Network default started
启动成功了，进行查看：
[root@localhost ~]# virsh net-list
Name State Autostart Persistent
----------------------------------------------------------
default active no yes
最后启动KVM虚拟机就好了：
[root@localhost ~]# virsh start centos7.0
Domain centos7.0 started
图形化界面查看，也已经成功：
