aufs-example

mkdir mnt

sudo mount -t aufs -o dirs=./writable:./readonly none ./mnt

create new file

cd mnt

sudo touch newfile

cd -

ls ./readonly
readme

ls ./writable
newfile  writeme

modify readonly file

cd mnt

sudo vi readme
hello readme
newline

cd -

cat readonly/readme
hello readme

ls ./readonly
readme

ls ./writable
newfile  readme  writeme

cat ./writable/readme
hello readme
newline

delete file

cd mnt

sudo rm readme

ls
newfile  writeme

cd -

ls ./readonly
readme

ls ./writable
newfile  writeme

ll ./writable
total 20
drwxr-xr-x 4 root root 4096 Oct 18 09:37 ./
drwxr-xr-x 6 root root 4096 Oct 18 09:26 ../
-rw-r--r-- 1 root root    0 Oct 18 09:28 newfile
-r--r--r-- 2 root root    0 Oct 18 09:27 .wh.readme
-r--r--r-- 2 root root    0 Oct 18 09:27 .wh..wh.aufs
drwx------ 2 root root 4096 Oct 18 09:27 .wh..wh.orph/
drwx------ 2 root root 4096 Oct 18 09:27 .wh..wh.plnk/
-rw-r--r-- 1 root root   13 Oct 18 09:26 writeme