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前言

很多厂商没有吧文件系统的构建方法开源出来，只是提供了一个rootfs.img的固件包，这不利于我们做二次开发，本文章实现一个自己构建的文件系统，并移植到RK的平台上使用

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一、官网下载ubuntu-base

http://cdimage.ubuntu.com/ubuntu-base/releases/
本文章使用的是：buntu-base-20.04.5-base-arm64.tar.gz
解压：

mkdir ubuntu_rootfs
tar -zxvf ubuntu-base-20.04.5-base-arm64.tar.gz -C ubuntu_rootfs

二、挂载并构建文件系统

2.1、配置构建文件系统环境

配置网络配置

cp /etc/resolv.conf  ubuntu_rootfs/etc/

配置仿真开发环境

sudo apt install qemu-user-static

sudo cp /usr/bin/qemu-aarch64-static ubuntu_rootfs/usr/bin/

更换软件源

sudo vim ubuntu_rootfs/etc/apt/sources.list

deb http://mirrors.aliyun.com/ubuntu-ports/ focal main restricted
deb http://mirrors.aliyun.com/ubuntu-ports/ focal-updates main restricted
deb http://mirrors.aliyun.com/ubuntu-ports/ focal universe
deb http://mirrors.aliyun.com/ubuntu-ports/ focal-updates universe
deb http://mirrors.aliyun.com/ubuntu-ports/ focal multiverse
deb http://mirrors.aliyun.com/ubuntu-ports/ focal-updates multiverse
deb http://mirrors.aliyun.com/ubuntu-ports/ focal-backports main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu-ports/ focal-security main restricted
deb http://mirrors.aliyun.com/ubuntu-ports/ focal-security universe
deb http://mirrors.aliyun.com/ubuntu-ports/ focal-security multiverse

2.2、编写挂载脚本mount.sh并安装相关工具

挂载根文件系统运行需要的设备和目录

#!/bin/bash
function mnt() {
    echo "MOUNTING"
    sudo mount -t proc /proc ${2}proc
    sudo mount -t sysfs /sys ${2}sys
    sudo mount -o bind /dev ${2}dev
    #sudo mount -t devpts -o gid=5,mode=620 devpts ${2}dev/pts
    sudo mount -o bind /dev/pts ${2}dev/pts
    sudo chroot ${2}
}
function umnt() {
    echo "UNMOUNTING"
    sudo umount ${2}proc
    sudo umount ${2}sys
    sudo umount ${2}dev/pts
    sudo umount ${2}dev
}
if [ "$1" == "-m" ] && [ -n "$2" ];
then
        mnt $1 $2
elif [ "$1" == "-u" ] && [ -n "$2" ];
then
        umnt $1 $2
else
        echo ""
        echo "Either 1'st, 2'nd or both parameters were missing"
        echo ""
        echo "1'st parameter can be one of these: -m(mount) OR -u(umount)"
        echo "2'nd parameter is the full path of rootfs directory(with tralling '/')"
        echo ""
        echo "For example: ch-mount -m /media/sdcard"
        echo ""
        echo 1st parameter : ${1}
        echo 2nd parameter : $[2]
fi

添加执行权限并挂载文件系统

sudo chmod +x mount.sh
./mount.sh -m ubuntu_rootfs/

挂载之后，开始安装文件系统中必要的一些软件

apt update

apt upgrade

apt install sudo vim udev net-tools ethtool udhcpc netplan.io language-pack-en-base language-pack-zh-han* iputils-ping openssh-sftp-server  ntp usbutils alsa-utils libmtp9    

安装的过程中会让你选择地区和时区

亚洲地区选择：6，Asia
中国时区选择：70，Shanghai
等待编译完成即可

2.3、轻量级的桌面环境 lubuntu-desktop

嵌入式平台选择轻量级的桌面环境lubuntu-desktop安装

apt install lubuntu-desktop

2.4、卸载一些不必要的软件

apt-get remove --purge lubuntu-update-notifier 

apt-get remove --purge libreoffice* 

2.5、添加用户

舔加用户

adduser ubuntu   

增加管理员权限

adduser ubuntu sudo  

2.6 、允许root用户登录桌面

gdm3设置允许root用户登录桌面,添加AllowRoot=true

vim /etc/gdm3/custom.conf

...
# Uncomment the line below to turn on debugging
# More verbose logs
# Additionally lets the X server dump core if it crashes
#Enable=true
AllowRoot=true 

vim /etc/pam.d/gdm-password 

注释：#auth required pam_succeed_if.so user != root quiet_success

#%PAM-1.0
auth    requisite       pam_nologin.so
#auth   required        pam_succeed_if.so user != root quiet_success
@include common-auth
auth    optional   

2.7、串口自动登录

vim /lib/systemd/system/serial-getty\@.service

注释：ExecStart=-/sbin/agetty -o ‘-p – \u’ --keep-baud 115200,38400,9600 %I $TERM
修改：ExecStart=-/sbin/agetty --autologin root --noclear %I $TERM

[Service]
# The '-o' option value tells agetty to replace 'login' arguments with an
# option to preserve environment (-p), followed by '--' for safety, and then
# the entered username.
#ExecStart=-/sbin/agetty -o '-p -- \\u' --keep-baud 115200,38400,9600 %I $TERM
ExecStart=-/sbin/agetty --autologin root --noclear %I $TERM
Type=idle
Restart=always
UtmpIdentifier=%I
TTYPath=/dev/%I
TTYReset=yes
TTYVHangup=yes
KillMode=process
IgnoreSIGPIPE=no
SendSIGHUP=yes

最后关闭自动休眠

sudo systemctl mask sleep.target suspend.target hibernate.target hybrid-sleep.target

2.8、添加分区释放的系统服务(重要)

通过实验，rootfs分区烧录后，只有固件本身大小，需要做分区释放

vim etc/init.d/resize2fs.sh

#!/bin/bash -e 
# resize filesystem mmcblk0p6
if [ ! -e "/usr/local/boot_flag" ] ;
then
  echo "Resizing /dev/mmcblk0p6..."
  resize2fs /dev/mmcblk0p6
  touch /usr/local/boot_flag
fi

添加执行权限

chmod +x etc/init.d/resize2fs.sh

创建服务去运行脚本

vim lib/systemd/system/resize2fs.service

#start
[Unit]
Description=Setup rockchip platform environment
Before=lightdm.service
After=resize-helper.service
[Service]
Type=simple
ExecStart=/etc/init.d/resize2fs.sh
[Install]
WantedBy=multi-user.target
#end

#退出根文件系统

exit

#卸载挂载的根文件系统

./mount.sh -u ubuntu_rootfs/

三、制作文件系统rootfs分区固件

3.1、创建一个空镜像文件

dd if=/dev/zero of=ubuntu_rootfs.img bs=1M count=8192‬

将该文件格式化为ext4文件系统

mkfs.ext4 ubuntu_rootfs.img

3.2、将镜像文件挂载到空文件

mkdir ubuntu_base_rootfs

chmod 777 ubuntu_base_rootfs

mount ubuntu_rootfs.img ubuntu_base_rootfs

cp -rfp ubuntu_rootfs/* ubuntu_base_rootfs/

umount ubuntu_base_rootfs/

3.3、修复及检测镜像文件系统

修复及检测镜像文件系统

e2fsck -p -f ubuntu_rootfs.img

resize2fs减小镜像文件的大小，上述的2.8小节中的释放rootfs分区大小与这里减少文件大小相关。

resize2fs -M ubuntu_rootfs.img

查看大小

du -sh ubuntu_rootfs.img

rootfs# du -sh ubuntu_rootfs.img 
5.0G	ubuntu_rootfs.img