I use Ubuntu Studio 18.04.2, with extended support time, in 2 desktop PCs and 1 laptop PC.
But... One of my desktop PC is an old BIOS mounted HDD installation.
I want to know if it is possible to convert all that installation into a UEFI installation, without to lose any data and without to have to format some partition.
I am going to assume that you have things set up on your Ubuntu machine, and don't want to do a full re-install. Assuming that you can use a second drive is to do a fresh minimal install of 18.04.2, which will set up the EFI partition and boot instructions, and then rsync your old install on top. There will be a little bit of checking that your EFI partition points at a valid kernel in the installation, but it saves re-configuring everything. I have done it twice, and it has worked both times (with a bit of fiddling).
