关于使用nfs挂载文件系统的问题！

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   我使用的硬件平台是AM335X starter kit ，SDK版本使用的是04版本（ti-processor-sdk-linux-am335x-evm-04.00.00.04-Linux-x86-Install.bin）官网上最新的SDK，现在编译了uboot和kernel，现在想通过nfs挂载文件系统，现在遇到的问题是：
[    6.172931] IPv6: ADDRCONF(NETDEV_CHANGE): eth0: link becomes ready
[    6.202864] IP-Config: Complete:
[    6.206146]      device=eth0, hwaddr=c4:ed:ba:8b:76:95, ipaddr=192.168.1.199, mask=255.255.255.0, gw=192.168.1.1
[    6.216755]      host=192.168.1.199, domain=, nis-domain=(none)
[    6.222727]      bootserver=192.168.155.0, rootserver=192.168.1.155, rootpath=
[    6.230809] lis3_reg: disabling
[    6.234206] vwl1271: disabling
[    6.237682] ALSA device list:
[    6.240683]   No soundcards found.
[    8.330196] VFS: Mounted root (nfs filesystem) on device 0:15.
[    8.337056] devtmpfs: mounted
[    8.341127] Freeing unused kernel memory: 304K (c08b2000 - c08fe000)
[    8.347644] This architecture does not have kernel memory protection.
[    8.640540] systemd[1]: System time before build time, advancing clock.
[    8.691890] systemd[1]: Failed to mount tmpfs at /sys/fs/cgroup: No such file or directory
[    8.703599] systemd[1]: Failed to mount cgroup at /sys/fs/cgroup/systemd: No such file or directory
[!!!!!!] Failed to mount API filesystems, freezing.
[    8.753079] systemd[1]: Freezing execution.
[   30.083735] cpsw 4a100000.ethernet eth0: Link is Down
[ 153.953531] random: crng init done