Question: I have a QEMU image `myserver.img` that is about 20GiB. The file serves as a "virtual" hard disk for the server. Now the first 512 bytes contain the MBR, and I am trying to overwrite those bytes with zeroes. On a normal disks, this one would work:

```
dd if=/dev/zero of=/dev/sda bs=512 count=1

```

But when I try that on the image file, the file gets overwritten and is only 512 bytes in size (instead of 20GiB). Is there a way to change only the first 512 bytes, preferably with `dd`?

Answer: 
There are some commercial web interfaces for managing linux servers.  

[cPanel](http://www.cpanel.net/) and [DirectAdmin](http://www.directadmin.com/) are the most popular examples.

You can have a shell in the browser using something like [Gate One](https://github.com/liftoff/GateOne) ([video demo](http://vimeo.com/24857127)).

There is also [Zentyal](http://www.zentyal.org/), a linux distribution that was designed to be administered through a web-interface.
There's [Webmin](http://www.webmin.com/), but personally I don't fancy the way it does things. Your mileage may wary.