dm6446单板启动后，nfs挂载错误。这一般如何解决？
IP-Config: Complete:
device=eth0, addr=10.1.0.102, mask=255.255.255.0, gw=10.1.0.1,
host=10.1.0.102, domain=, nis-domain=(none),
bootserver=0.0.0.0, rootserver=0.0.0.0, rootpath=
Looking up port of RPC 100003/2 on 0.0.0.0
portmap: server 0.0.0.0 not responding, timed out
Root-NFS: Unable to get nfsd port number from server, using default
Looking up port of RPC 100005/1 on 0.0.0.0
portmap: server 0.0.0.0 not responding, timed out
Root-NFS: Unable to get mountd port number from server, using default
mount: server 0.0.0.0 not responding, timed out
Root-NFS: Server returned error -5 while mounting /tftpboot/$(nfshost):$(rootpath)
VFS: Unable to mount root fs via NFS, trying floppy.
VFS: Cannot open root device "nfs" or unknown-block(2,0)
Please append a correct "root=" boot option
Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(2,0)
