请教一个奇怪的文件系统问题!

sunday7808

u-boot-1.0.0  linux-2.6.16 busybox-1.4.2这是我移植的版本,在at91rm9200 板子上跑起来之后出现了shell提示符,但是看不到文件夹下面是我的启动信息
init started:  BusyBox v1.4.2 (2007-09-10 15:50:28 CST) multi-call binary
Starting pid 21, console /dev/ttyS0: '/etc/init.d/rcS'
Starting pid 24, console /dev/ttyS0: '/bin/sh'


BusyBox v1.4.2 (2007-09-10 15:50:28 CST) Built-in shell (ash)
Enter 'help' for a list of built-in commands.

# ls
# cd bin
# date
Thu Jan  1 00:17:45 UTC 1970
#
linuxrc文件就是最简单的,inittab如下
::sysinit:/etc/init.d/rcS
tty0::respawn:/sbin/getty 115200 tty0
::askfirst:-/bin/sh
tty1::askfirst:-/bin/sh
::restart:/bin/init
不知道什么原因 ls,cd bin等命令都没反应,请高人指点一下!