AnotherUnionFS (aufs)

# mount -t aufs -o dirs=/dev/shm:/mnt=ro none /mnt
 
# ls -la /mnt
total 4
drwxrwxrwt  3 root root   80 2009-10-11 17:31 .
drwxr-xr-x 22 root root 4096 2009-10-11 14:06 ..
-rw-r--r--  1 root root    0 2009-10-11 17:25 muh
 
# echo "a" > /mnt/muh
 
# echo "b" > /mnt/muh2
 
# ls -la /mnt/
total 12
drwxrwxrwt  3 root root  120 2009-10-11 17:31 .
drwxr-xr-x 22 root root 4096 2009-10-11 14:06 ..
-rw-r--r--  1 root root   2 2009-10-11 17:31 muh
-rw-r--r--  1 root root   2 2009-10-11 17:31 muh2
 
# umount /mnt
 
# ls -la /mnt/
total 8
drwxr-xr-x  2 root root 4096 2009-10-11 17:25 .
drwxr-xr-x 22 root root 4096 2009-10-11 14:06 ..
-rw-r--r--  1 root root    0 2009-10-11 17:25 muh