docker overlay 文件系统原理

mkdir /lower{1,2,3}
mkdir /upper /work /merged

mount -t overlay overlay -o lowerdir=/lower1:/lower2:/lower3,upperdir=/upper,workdir=/work /merged

df -h

touch /merged/123.txt

ls -l /upper/
ls -l /lower*

umount /merged

mount -t overlay overlay -o lowerdir=/lower1:/lower2:/lower3,workdir=/work /merged

touch /merged/456.txt

# touch: cannot touch ‘/merged/456.txt‘: Read-only file system