我的板子是mini2440。
ubuntu
直接进入mini2440系统，在板上与虚拟机互ping可以。
在虚拟机上执行
sudo mount localhost:/home/linux/root_qtopia/ /mnt，挂载是成功的。
网络选择桥接。
复位，进入supervivi
设置参数：
param set linux_cmd_line "console=ttySAC0 root=/dev/nfs nfsroot=192.168.1.104:/home/fzu/linux/root_qtoqia ip=192.168.1.230:192.168.1.104:192.168.1.104:255.255.255.0:mini2440:eth0:off"
挂载根文件系统时老是出现下面的错误：
TCP cubic registered
lib80211: common routines for IEEE802.11 drivers
s3c2410-rtc s3c2410-rtc: setting system clock to 2005-12-08 19:30:19 UTC (113407
0219)
eth0: link down
IP-Config: Complete:
  device=eth0, addr=192.168.1.230, mask=255.255.255.0, gw=192.168.1.104,
  host=fzu, domain=, nis-domain=(none),
  bootserver=192.168.1.104, rootserver=192.168.1.104, rootpath=
Looking up port of RPC 100003/2 on 192.168.1.104
eth0: link up, 100Mbps, full-duplex, lpa 0x45E1
Looking up port of RPC 100005/1 on 192.168.1.104
Root-NFS: Server returned error -13 while mounting /home/fzu/linux/root_qtoqia
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; here are the available partitions:
1f00 256 mtdblock0 (driver?)
1f01 128 mtdblock1 (driver?)
1f02 5120 mtdblock2 (driver?)
1f03 125568 mtdblock3 (driver?)
1f04 131072 mtdblock4 (driver?)
Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(2,0)
Backtrace:
[<c0035270>] (dump_backtrace+0x0/0x10c) from [<c03958f0>] (dump_stack+0x18/0x1c)

r7:c39230cb r6:c0503ed0 r5:c3923000 r4:c3823f40
[<c03958d8>] (dump_stack+0x0/0x1c) from [<c0395940>] (panic+0x4c/0x134)
[<c03958f4>] (panic+0x0/0x134) from [<c0008e9c>] (mount_block_root+0x178/0x234)
r3:00000000 r2:c383692c r1:c3823f40 r0:c0453700
[<c0008d24>] (mount_block_root+0x0/0x234) from [<c0009008>] (mount_root+0xb0/0xf
4)
[<c0008f58>] (mount_root+0x0/0xf4) from [<c0009144>] (prepare_namespace+0xf8/0x1
90)
r7:c05038a0 r6:c0021808 r5:c0021808 r4:c0021818
[<c000904c>] (prepare_namespace+0x0/0x190) from [<c00084c0>] (kernel_init+0xf0/0
x124)
r7:00000000 r6:c00200dc r5:c00205d4 r4:c00205d4
[<c00083d0>] (kernel_init+0x0/0x124) from [<c004d1a4>] (do_exit+0x0/0x62c)
网上查了一些资料说
“error 13的错误是access deny
连接被阻止，关掉nfs server主机的防火墙”
然后我就执行apt-get remove iptables
重启nfs服务，但还是出错同样的错误。

用"sudo ufw disable"试试看?我同学用Ubuntu似乎是这样关的。

谢谢~
不过ubuntu默认防火墙就是关闭的啊，
我查看了防火墙的状态，它已经是关闭状态了。

sudo mount localhost:/home/linux/root_qtopia/ /mnt，挂载是成功的。
nfsroot=192.168.1.104:/home/fzu/linux/root_qtoqia
---------------------------------------------------------------------
为摄用localhost测试用的路径和最后的引导参数里的路径不一样?
/home/linux/root_qtopia      vs      /home/fzu/linux/root_qtoqia
/etc/exports里的权限确认了么?

不是这个原因、那个是我敲错了。
在ubuntu上挂载/home/fzu/linux/root_qtoqia是没问题的。

我也是遇到这个问题，现在头都大了

http://www.aiothome.net/read.php?tid=6795&page=e&#a

看看这篇帖子，要求版主加精的。

问题解决了。
console=ttySAC0 root=/dev/nfs nfsroot=192.168.1.104:/home/fzu/linux/root_qtoqia后面敲错了一个字符root_qtopia
其实查出这个错误error 13是access deny也就是说你要挂载的目录不是你/etc/exports中指定的目录，这时你就要检查一下输入是不是有错，大意了我。