```
> md5sum U2.zip
31e8feb8e5a501e5302a7ac983336a24  U2.zip
> shasum U2.zip
409499f04d7bb853cc12991f209bad2d58478cf8  U2.zip
```

unpack zip archive:
```
> unzip U2.zip
...
> md5sum U2.img
34126162163acea9b3e8130ac09f5340  U2.img
> shasum U2.img
e809c3186acc3e8fadfa8feb2c5decad17d147fe  U2.img
```
mount image read-only:
```
> sudo mount -o ro ./U2.img ./mnt
> touch ReadMe.md
touch: cannot touch 'ReadMe.md': Read-only file system
```