The Lubuntu manual page can be found at https://manual.lubuntu.me/stable/1/1.3/installation.html
I won't repeat what's listed there, and I'm writing this as I complete a QA-test install of groovy using today's daily.
I've performed two QA-test installs on this box in the last hour which resulted in the following partitions ; details viewed in KDE Partition Manager
- /dev/sda1 fat32 300mb ESP (uEFI System Partition)
- /dev/sda2 ext4 74gb ext4 (initial full disk install)
- /dev/sda3 ext4 45gb ext4 (install alongside testcase)
I'm going to erase that anyway.
Start calamares
(the installer used by Lubuntu)
Opt for Manual Partitioning.. and create new partition table (GPT)
Creating partitions looks like

sda1: ESP
- I create a 512MB EFI system partition (larger than default; I've had issues on some boxes with smaller so I've increased size since)
- Select mount point as
/boot/efi
- click both BIOS-GRUB & BOOT options in the flag section.
sda2: /
- I create a ext4 partition with rest of disk space (where I'll install to).
- Select mount point as /
- I click both options available BIOS-GRUB & BOOT in the flag section too
I don't believe I need to select both options for both, but both those options I find easier to remember & work, so I just do that.
Click next, following prompts (giving my username, hostname etc) and reboot when it tells me to. Eject my thumb-drive when told to, and reboot into my freshly installed Lubuntu groovy system.
I login, test the system & update my QA-test entry report on iso.qa.ubuntu.com. I'm using groovy as it's useful for a QA-test (a little early for me to be thinking about 20.04.2) but it'll be identical to a focal install.
/root
, this is usually a directory a directory under '/' and not given it's own directory as it's usually empty or near empty on most installs. It maybe you meant "/" which is called root, but differs to "/root/" Have you tried the manual manual.lubuntu.me/stable/1/1.3/installation.html As I recall there are two flags I believe for /, one for /boot/efi (boot & bios-grub), but whilst I've done I think 5 successful installs this last week, I know I've had to adjust the flags at least once (even twice; ie. back & adjust until installer is happy)/boot/EFI
partition ?