I.MX6 Ubuntu core porting

/***********************************************************************
 *                      I.MX6 Ubuntu core porting
 * 说明：
 *     之前查资料查到了Ubuntu core的资料，然后一直想尝试将Ubuntu core放到
 * I.MX6中，当然也想将其放到OK335xS中，于是今天花点时间将其放入I.MX6中。
 *
 *                                     2016-4-16 深圳 南山平山村 曾剑锋
 **********************************************************************/

一、参考文档：
    1. 移植ubuntu core到Arm开发板
        http://blog.csdn.net/kickxxx/article/details/15341079
    2. Ubuntu 14.04 for i.MX6
        https://support.bluetechnix.at/wiki/Ubuntu_14.04_for_i.MX6

二、download:
    1. https://developer.ubuntu.com/en/snappy/
    2. http://cdimage.ubuntu.com/ubuntu-base/releases/12.04/release/
    3. http://mirror1.ku.ac.th/ubuntu-cdimages/ubuntu-core/

三、解压打包：
    tar zxvf ubuntu-core-12.04.4-core-armhf.tar.gz -C rootfs/
    cd rootfs
    tar jcvf rootfs.tar.bz2 *
    mv rootfs.tar.bz2 ..
    cd ..
    cp rootfs.tar.bz2 /mnt/hgfs/Desktop/

四、error
    1. error1：
        1. 内核打印信息在如下位置停止了：
            ......
            EXT3-fs (mmcblk0p1): warning: checktime reached, running e2fsck is recommended  
            kjournald starting.  Commit interval 5 seconds                                  
            EXT3-fs (mmcblk0p1): using internal journal                                     
            EXT3-fs (mmcblk0p1): mounted filesystem with writeback data mode                
            VFS: Mounted root (ext3 filesystem) on device 179:1.                            
            Freeing init memory: 208K                                                       
            init: Unable to mount /dev filesystem: No such device     
        2. 问题原因：
            debug的终端口没有打开，需要另外配置console。
        3. cat /etc/init/ttymxc.conf
            # 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 (
                        not-container or
                        container CONTAINER=lxc or
                        container CONTAINER=lxc-libvirt)
            
            stop on runlevel [!2345]
            
            respawn
            exec /sbin/getty -L 115200 ttymxc0 vt102
        4. cat /etc/init.d/rc.local    
            ......
            start ttymxc0
            ......
    2. error2：
        1. root用户需要密码，去掉该功能；
        2. cat /etc/passwd
            root::0:0:root:/root:/bin/bash
            daemon:x:1:1:daemon:/usr/sbin:/bin/sh
            bin:x:2:2:bin:/bin:/bin/sh
            sys:x:3:3:sys:/dev:/bin/sh
            sync:x:4:65534:sync:/bin:/bin/sync
            games:x:5:60:games:/usr/games:/bin/sh
            man:x:6:12:man:/var/cache/man:/bin/sh
            lp:x:7:7:lp:/var/spool/lpd:/bin/sh
            mail:x:8:8:mail:/var/mail:/bin/sh
            news:x:9:9:news:/var/spool/news:/bin/sh
            uucp:x:10:10:uucp:/var/spool/uucp:/bin/sh
            proxy:x:13:13:proxy:/bin:/bin/sh
            www-data:x:33:33:www-data:/var/www:/bin/sh
            backup:x:34:34:backup:/var/backups:/bin/sh
            list:x:38:38:Mailing List Manager:/var/list:/bin/sh
            irc:x:39:39:ircd:/var/run/ircd:/bin/sh
            gnats:x:41:41:Gnats Bug-Reporting System (admin):/var/lib/gnats:/bin/sh
            nobody:x:65534:65534:nobody:/nonexistent:/bin/sh
            libuuid:x:100:101::/var/lib/libuuid:/bin/sh
    3. error3：
        1. 第一次运行现象：
            ......
            EXT3-fs: barriers not enabled                                                   
            kjournald starting.  Commit interval 5 seconds                                  
            EXT3-fs (mmcblk0p1): warning: checktime reached, running e2fsck is recommended  
            EXT3-fs (mmcblk0p1): using internal journal                                     
            EXT3-fs (mmcblk0p1): mounted filesystem with writeback data mode                
            VFS: Mounted root (ext3 filesystem) on device 179:1.                            
            Freeing init memory: 208K                                                       
            init: Unable to mount /dev filesystem: No such device                           
            start: Unknown job: ttymxc0                                                     
                                                                                            
            Ubuntu 12.04.4 LTS localhost.localdomain ttymxc0                                
                                                                                            
            localhost login: 
        2. 第二次运行现象：
            ......
            EXT3-fs: barriers not enabled                                                   
            kjournald starting.  Commit interval 5 seconds                                  
            EXT3-fs (mmcblk0p1): warning: checktime reached, running e2fsck is recommended  
            EXT3-fs (mmcblk0p1): using internal journal                                     
            EXT3-fs (mmcblk0p1): recovery complete                                          
            EXT3-fs (mmcblk0p1): mounted filesystem with writeback data mode                
            VFS: Mounted root (ext3 filesystem) on device 179:1.                            
            Freeing init memory: 208K                                                       
                                                                                            
            Ubuntu 12.04.4 LTS localhost.localdomain ttymxc0                                
                                                                                            
            localhost login: 
        3. 目前没有花时间来分析两次现象不同的原因。