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I have an existing CentOS 6 installation working wonderfully and its owner now wants to add a separate Debian installation onto the same machine. He only accesses this host via the command line and via a NoMachine VNC-type GUI connection, since it's located in a data center and thus out of reach.

My questions:

  1. Can I create a "hot partition" on the existing CentOS 6 installation without destroying what we have now?

  2. If I can safely add a new partition, is there any tool or method the user could use to choose which OS it will boot into? Something like a boot picker. Remember he does not have physical access to the machine.

I'm coming from a Mac/Windows background and thus don't know the answers. Suggestions or ideas are welcome.

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  1. I would suggest using some form of virtualiazation in your existing CentOS 6 system, like OpenVZ -or maybe even VirtualBox (since you can access the host via VNC) and installing a Debian system as a guest.

  2. No. You can't access a boot-loader via SSH or VNC client, because at the stage where the OS is being "picked", neither the SSH server nor the VNC server are initialized. It would be possible if the data center that the box is located in, offered some kind of iKVM capabilities, which would give you more control over the host.

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I have an idea for the second question , not 100% correct, but can resolve this issue in Indirect way

write script to change default OS in bootloader configuration when user want to change OS run this script and change this default bootloader option

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