A20 最小系统改造 为ubuntu-core-14.04-core-armhf.tar.gz
rootfs 下载：
http://cdimage.ubuntu.com/ubuntu-core/releases/14.04/release/ubuntu-core-14.04-core-armhf.tar.gz
$ wget http://cdimage.ubuntu.com/ubuntu-core/releases/14.04/release/ubuntu-core-14.04-core-armhf.tar.gz
$ cd xxxx_sdk/binaries/ && mkdir rootfs
$ cp ubuntu-core-14.04-core-armhf.tar.gz xxxx_sdk/binaries/rootfs/
$ cd rootfs/
$ sudo tar -zxvpf ubuntu-core-14.04-core-armhf.tar.gz
sudo vi etc/shadow
root:*:16176:0:99999:7::: //删除"*" //删除root密码
$ rm ubuntu-core-14.04-core-armhf.tar.gz
2# 添加ubuntu1404-core 串口登录问题
$ sudo vi etc/rc.local
#!/bin/sh -e
#
# rc.local
#
# This script is executed at the end of each multiuser runlevel.
# Make sure that the script will "exit 0" on success or any other
# value on error.
#
# In order to enable or disable this script just change the execution
# bits.
#
# By default this script does nothing.
start ttyS0
exit 0
$ sudo vi /etc/init/ttyS0.conf //内容如下：
# console - getty
#
# This service maintains a getty on console from the point the system is
# started until it is shut down again.
start on stopped rc RUNLEVEL=[2345] and container CONTAINER=lxc
stop on runlevel [!2345]
respawn
exec /sbin/getty -L 115200 ttyS0 vt100###压缩rootfs
$ cd .. && sudo tar -czvpf ubuntu1404_server.tar.gz rootfs
$ vi products/a20/a20-debian-server/envsetup.sh
export CB_PRODUCT_ROOTFS_IMAGE=${CB_PACKAGES_DIR}/ubuntu1404_server.tar.gz //此处修改
替换products/a20/a20-debian-server/overlay 文件夹！！！！下载地址：http://download.csdn.net/detail/u010402372/9307531
$ cp overlay_bak.tar.gz products/a20/a20-debian-server/ && cd products/a20/a20-debian-server/
$ rm overlay -rf //先rm
$ tar -xzvpf overlay_bak.tar.gz
效果：
usb open backing file: /dev/mmcblk0p1, 0xdf1df600
<6>g_mass_storage gadget: Mass Storage Function, version: 2009/09/11
<6>g_mass_storage gadget: Number of LUNs=1
<6> lun0: LUN: removable file: /dev/mmcblk0p1
ep_matches, wrn: endpoint already claimed, ep(0xc0887f34, 0xbf0e72e4, ep1-bulk)
<6>g_mass_storage gadget: Mass Storage Gadget, version: 2009/09/11
<4>g_mass_storage gadget: userspace failed to provide iSerialNumber
<6>g_mass_storage gadget: g_mass_storage ready
WRN:L2762(/home/dou/lins/linux-sdk-card/linux-sunxi/drivers/usb/sunxi_usb/udc/sw_udc.c):ERR: usb device is not active
* Stopping System V runlevel compatibility[ OK ]
Ubuntu1404 GNU/Linux a20 3.4.79 wheezy
The default login:
More support plese by jiangdou
ubuntu login: <7>eth0: no IPv6 routers present
Ubuntu1404 GNU/Linux a20 3.4.79 wheezy
The default login:
More support plese by jiangdou
ubuntu login: root
Last login: Sat Nov 28 04:38:24 UTC 2015 on ttyS0
Welcome to Ubuntu 14.04 LTS (GNU/Linux 3.4.79 armv7l)
* Documentation: https://help.ubuntu.com/
root@ubuntu:~#
root@ubuntu:~#
# 以下可选可不选择！！
a:在启动命令文件 /etc/rc.local 中插入一行：mount -o remount -o noatime / ，以提升性能同时防止频繁擦写弄坏 SD 卡
b:删除root 密码
另一种是直接编辑/etc/shadow文件，/etc/shadow文件以加密的形式保存了各个用户的密码，如果密码为空则不允许使用密码登录。
用法示例：
$ sudo nano /etc/shadow
删除root那一行第一个与第二个冒号之间的内容
5# 选择开机加载驱动,或者不加载！！！
vi products/a20/a20-debian-server/overlay/etc/modules
注释掉！！前面加“#”