Kickstart - how to exit if an OS already exists

Question

I have what is surely a remedial question for anyone with more Linux experience. I need to check if an operating system is already installed in my kickstart script, and if so, prompt the user if they would like to continue (basically reinstall) or to exit.

What is the most efficient way to do this?

I was thinking of doing something like the following:

%pre
#!/bin/sh
if [ -f some_file ]; then
  read -p "An OS already exists, do you want to re-install?" yn
    case $yn in
        [Yy]* ) break;;
        [Nn]* ) exit;;
        * ) echo "Please answer yes or no.";;
    esac
fi

I'm not sure what file would be best to use in place of "some_file" in my example, or if this is even a good way to go about it.

Note that the reason I need to do this is because this Linux installation is part of a much larger automated installation so a user is not there to manually check if the OS exists already.

Answer 1

Where would the / filesystem reside, if an operating system were installed? Would it be in the same place on all the nodes you intend to install?

You could test for the presence of a partition:

[ -b /dev/sdXY ] && { do something ; }

Or a logical volume:

[ -b /dev/mapper/vg00/lvXYZ ] && { do something ; }

You could attempt to mount it, and test for the presence of a certain file:

mkdir /tmp/mt
if mount /dev/sdXY /tmp/mt && [ -f /tmp/mt/filename ]; then
      do something
fi

Answer 2

We simply set the BIOS boot order to HD followed by PXE.

This means the system will install from PXE at first boot, subsequent boots are from the installed OS.

When we need to reinstall, we just wipe the boot sector from within the OS then reboot.