问题：启动过程中停留在nfs: server not responding still trying错误
原因：nfsroot需要内核使用网卡设置，实际上网卡在进入runlevel之前已经被配置了，重新配置网卡将使得root丢失
解决：将PXE启动配置和/etc/network/interfaces的配置成相同静态地址
----------------- PXE --------------------
KERNEL boot/vbuild/vmlinuz-2.6.32-5-amd64
APPEND initrd=boot/vstream/initrd.img-2.6.32-5-amd64 rw nolock boot=nfs root=/dev/nfs nfsroot=192.168.4.234:/mnt/local/vbuildengine ip=192.168.4.84::192.168.4.1:255.255.255.0:debianbuild:eth0:off
----------------- /etc/network/interface ----------------
allow-hotplug eth0
iface eth0 inet static
address 192.168.4.84
netmask 255.255.255.0
gateway 192.168.4.1