I don't know why but, umount is not working in docker.

```
umount: loop3/: must be superuser to umount

```

Let me share one more thing that is 
It creates `loop3` under `/mnt/loop3` in real machine. Which is most unexpected thing for me, because promises pure virtual environment. 

Why? Any solution?

### Scenario :

I created docker `ubuntu:13.04` to create cross compilation environment. 

* Docker Linux machine (ubuntu):

```
Linux 626089eadfeb 3.10.45-1-lts #1 SMP Fri Jun 27 06:44:23 UTC 2014 x86_64 x86_64 x86_64 GNU/Linux

```
* Linux Machine (rch Linux):

```
Linux localhost 3.10.45-1-lts #1 SMP Fri Jun 27 06:44:23 UTC 2014 x86_64 GNU/Linux

```

### Docker Info

```
Client version: 1.0.1
Client API version: 1.12
Go version (client): go1.3
Git commit (client): 990021a
Server version: 1.0.1
Server API version: 1.12
Go version (server): go1.3
Git commit (server): 990021a

```