On a stock 5.2 upgrade to 6.0 on a low disk space box,
the installer did not a) complain about running out of space
b) install the kernel.
The only indication that something went wrong was the
"install boot loader" item failed.
We will need more information on how your system is setup. Such as a
listing of partitions and sizes as well as how much disk space was
available before the upgrade.