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's some commercial offerings which try to deliver this (Tivoli, unicenter TNG, Openview, BMC) IME, they mostly deliver this by being a jack of all trades rather than a master of one.

> 
> Services monitoring: for each server I want to see all running daemons and be able to start/stop/restart them (just like windows services)
> 
> 
> 

Nagios, Munin, Cacti

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> Have a interactive web-based shell allowing to execute commands to multiple machines directly from my browser
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Canonical Landscape, and while it's not web-based (how 'interactive' should system admin be?) there's clusterssh

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> Fast scripting: be able to create scripts directly in my browser and run and deploy them to all my machines
> 
> 
> 

Isn't that the same as the previous requirement?
There's [Webmin](http://www.webmin.com/), but personally I don't fancy the way it does things. Your mileage may wary.