[SOLVED] boot loop after install alongside 18.04

[phonic-otg]

Hey I just encountered a new install first for me.
I have installed 20.04 on the free space (81Gb)of my friends desktop which was running 18.04, as he was having issues with Amarok not playing nice.
After the install on the first run it posted the grub menu and when selecting the 20.04 image to load, it would start the process then the next thing it has rebooted back to the grub menu.
This time selecting advanced options and selecting the first image, it began loading the image but, a quick message posted which was something like "decode failed" it was super quick, only to be rebooted again.
Went in to recover mode for the 20.04 kernel, the next time, and got to the root GUI with networking and did an update (158 files) and updated grub with command update-grub.
When grub posted I selected the 20.04 image it rebooted then went to a black screen. Restarted from PC powerbutton.
I can boot into the 18.04 image fine and the recover mode for 20.04 but not the regular kerne
All suggegestions requested.

[phonic-otg]

OK I found a temporary solution here .> https://itsfoss.com/fix-ubuntu-freezing/

It was a mater of editing the 20.04 kernel listing in grub to have nomodeset.

EDIT: Alas this just allowed me to boot the20.04 image (5.4.0-33-generic) and get most of it configured like his 18.04 installation with all of his personal data copied for browsers, email and music.
Unfortunately the "nomodeset" edit in grub is temporary as well we discovered that the Discrete graphics card was not being used.

He is using a Ryzen 5 2400G APU with vega graphics so the monitor (primary display) is running from the Motherboards VGA I/O, which I assume is why "nomodeset" works temporarily.
His extra Graphics card is a Radeon RX560 that is connected to his TV via HDMI, that works as a dule monitor set-up in 18.04, but is not seen by 20.04.
Some guidance is sought.

[phonic-otg]

Question.
The 18.04 image sees the RX560 card and outputs to it but the 20.04 image does not. Is there away to reinstall 20.04 and keep the home folder data? Or find the way 18.04 has the settings and duplicate it in 20.04?

[Schwarzer Kater]

- Originally, did you install K20.04 on a seperate, new partition?
- If you added nomodeset to GRUB_CMDLINE_LINUX_DEFAULT in /etc/default/grub it should not be temporary.
- Did you try installing 20.04 with the "safe graphics" option from the live installer? And did you also select the non-free drivers during installation?

But honestly I cannot quite retrace what you have done by your description above, sorry…

[Don B. Cilly]

Is there away to reinstall 20.04 and keep the home folder data? Or find the way 18.04 has the settings and duplicate it in 20.04?

Just copy the 18.04 /home over to the 20.04 one. Best done while running 18.04.
If you have a lot of documents and stuff in /home, and don't want to copy those, just copy the hidden files and folders.
As in (from your /home)
cp -rf ./.[^.]* /media/user/whatevertheplaceiscalled/home/

Or, with Dolphin, select all (Ctrl.-a), deselect (Ctrl-click) the files/folders you don't want to copy over...

[phonic-otg]

All is well.
Schwarzer Kater, Yes it is on its own partition and non-free software also selected. Safe graphics was the only option to start from the installer on HIS system (mine has nicer hardware). Also, I edited in the grub MENU at boot options, not the persistent file.
Don B. Cilly, All his important files and the hidden browser, email and playlist folders were copied over in half an hour.

My quick fix solution was to have both Monitors inputs come from the Radeon RX560 and no boot problems.
He is happy with that and now is, loving, having a functional system again.
He is not interested in why his now current installation of 20.04 didn't dual output via APU graphics & GPU graphics as it did with 18.04, he is just happy it works with no issues other than learning a new music player as his Amarok broke (in 18.04) and was not starting up.
Thanks for the replies.