从0到1 构建bash linux 系统

下载linux 内核版本 4.9.6
内核目录/vm/custom2/linux-4.9.6$
make  x86_64_defconfig
make -j 8
在/vm/custom2/创建sysroot目录
mkdir -pv {bin,sbin,etc,proc,sys,usr/{bin,sbin}}
bash没有这些目录不会panic
/vm/custom2/目录下建立exportbin.sh
内容如下、
#!/bin/bash


if [ $# != 2 ] ; then
    echo "usage $0 PATH_TO_BINARY TARGET_FOLDER"
    exit 1
fi


PATH_TO_BINARY="$1"
TARGET_FOLDER="$2"


# if we cannot find the the binary we have to abort
if [ ! -f "$PATH_TO_BINARY" ] ; then
    echo "The file '$PATH_TO_BINARY' was not found. Aborting!"
    exit 1
fi


# copy the binary to the target folder
# create directories if required
echo "---> copy binary itself"
cp --parents -v "$PATH_TO_BINARY" "$TARGET_FOLDER"


# copy the required shared libs to the target folder
# create directories if required
echo "---> copy libraries"
for lib in `ldd "$PATH_TO_BINARY" | cut -d'>' -f2 | awk '{print $1}'` ; do
   if [ -f "$lib" ] ; then
        cp -v --parents "$lib" "$TARGET_FOLDER"
   fi  
done


# I'm on a 64bit system at home. the following code will be not required on a 32bit system.
# however, I've not tested that yet
# create lib64 - if required and link the content from lib to it
if [ ! -d "$TARGET_FOLDER/lib64" ] ; then
    mkdir -v "$TARGET_FOLDER/lib64"
fi
用于copy基本的c库
chmod +x exportbin.sh
然后到/vm/custom2/目录下
运行 
./exportbin.sh /bin/bash sysroot
其实可以自己编译bash，我使用ubuntu中的bash
下载 util-linux-2.29.2.tar.xz
首先安装ncurses


sudo apt install libncurses5-dev libncursesw5-dev


./configure --prefix=/vm/custom2/sysroot                   --without-python  
make
sudo make install
然后copy util用到so


librt.so.1 => /lib/x86_64-linux-gnu/librt.so.1
li@li-shuangbin:/vm/custom2/sysroot/lib/x86_64-linux-gnu$ cp -r /lib/x86_64-linux-gnu/librt.so.1 .


li@li-shuangbin:/vm/custom2/sysroot/lib/x86_64-linux-gnu$ ll /lib/x86_64-linux-gnu/librt.so.1
lrwxrwxrwx 1 root root 13 May 26  2016 /lib/x86_64-linux-gnu/librt.so.1 -> librt-2.19.so
li@li-shuangbin:/vm/custom2/sysroot/lib/x86_64-linux-gnu$  cp -r  /lib/x86_64-linux-gnu/librt-2.19.so .




li@li-shuangbin:/vm/custom2/sysroot/lib/x86_64-linux-gnu$ cp -r  /lib/x86_64-linux-gnu/libpthread.so.0 .
li@li-shuangbin:/vm/custom2/sysroot/lib/x86_64-linux-gnu$ ll /lib/x86_64-linux-gnu/libpthread.so.0 
lrwxrwxrwx 1 root root 18 May 26  2016 /lib/x86_64-linux-gnu/libpthread.so.0 -> libpthread-2.19.so*


li@li-shuangbin:/vm/custom2/sysroot/lib/x86_64-linux-gnu$ cp -r /lib/x86_64-linux-gnu/libpthread-2.19.so .


在/vm/custom2/sysroot下新建mkcpio.sh
内容如下
find . -print0     | cpio --null -ov --format=newc     | gzip -9 > ../obj/initramfs-bash-x86.cpio.gz


在/vm/custom2/sysroot下新建init
内容如下
#!/bin/bash
 
mount -t proc none /proc
mount -t sysfs none /sys
 
echo -e "\nBoot took $(cut -d' ' -f1 /proc/uptime) seconds\n"
mount -t devtmpfs none /dev 
exec /bin/bash




chmod +x init
chmod +x mkcpio.sh
然后运行 ./mkcpio.sh
新建硬盘
mkfs -t ext4 hda.img
mkdir mnt
sudo mount hda.img mnt
编译coreutils
cd coreutils-8.27/
./configure --prefix=/vm/custom2/sysroot 
make
sudo make install
exec switch_root /newroot /bin/systemd








sudo apt-get install intltool
sudo apt-get install libcap-dev
/vm/custom2/systemd-233$ ./autogen.sh 
./configure --prefix=/vm/custom2/sysroot            \
            --sysconfdir=/etc        \
            --localstatedir=/var     \
            --config-cache           \
            --with-rootprefix=       \
            --with-rootlibdir=/lib   \
            --enable-split-usr       \
            --disable-firstboot      \
            --disable-ldconfig       \
            --disable-sysusers       \
            --without-python         \
            --with-default-dnssec=no \
            --docdir=/usr/share/doc/systemd-233


在/vm/custom2/目录下，运行
qemu-system-x86_64 \
    -kernel linux-4.9.6/arch/x86_64/boot/bzImage \
    -initrd obj/initramfs-bash-x86.cpio.gz \
    -hda obj/hda.img -append root=/dev/sda 

如果没用有-append root=/dev/sda 
出现
 Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0)
其实原因是
  1.297807] VFS: Cannot open root device "(null)" or unknown-block(0,0): error -6
[    1.298684] Please append a correct "root=" boot option; here are the available partitions:
[    1.299651] 0800         1048576 sda [    1.300084]  driver: sd
[    1.300376] 0b00         1048575 sr0 [    1.300853]  driver: sr
[    1.301173] Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0)
启动脚本不必添加 -append root=/dev/sda 
因为qemu启动只有128MB Ram，需要改为

qemu-system-x86_64 \
    -m 1024 \
    -kernel linux-4.9.6/arch/x86_64/boot/bzImage \
    -initrd obj/initramfs-bash-x86.cpio.gz \
    -nographic -append "console=ttyS0"  \
    -enable-kvm  -hda obj/hda.img