How to choose kernel to boot

[mjd]

Hi all,

I have Rock64 2GB with Debian minimal Stretch on HDD, using the USB adapter from Pine64 shop.
System i even upgraded to buster/testing using just official Debian repo.
So far works excelent and I'm happy, except for the ancient kernel 4.14.

So here is my questions.
I plan to upgrade kernel, build it myself or wait for 4.18 from Ayufan.
But what if the new kernel will not boot, how can I recover?
Is it just possible to connect HDD to PC and change some conf file?

Another question is about HDMI.
Is it normal that I do not have output on TV (two tested) in early boot? Serial Console is needed to see SPI boot menu and his messages?
HDMI output starts workingvery late in 2-3 seconds before login.

Thanks for help for another ARM newbie?

[evilbunny]

But what if the new kernel will not boot, how can I recover?
Is it just possible to connect HDD to PC and change some conf file?

Yes, although you'll need to have something that can modify ext4 partitions, one way to do this is running a live linux distro on your pc etc, although if you have a serial dongle you can pick from different kernels on boot

Another question is about HDMI.
Is it normal that I do not have output on TV (two tested) in early boot? Serial Console is needed to see SPI boot menu and his messages?
HDMI output starts workingvery late  in 2-3 seconds before login.

Unfortunately serial is simpler than hdmi and it kicks in long before hdmi.

[mjd]

I'm Linux user so ext4 is not a problem

Is there any proven manual what have to do next? 

I'm affraid to put my services until I ensure that rescue of the failed booting procees is possible without overwrite everything by clean image.

[evilbunny]

I'm affraid to put my services until I ensure that rescue of the failed booting procees is possible without overwrite everything by clean image.

I'm unaware of any manuals but I would install an alternate kernel and flick back and forth between them until I was happy.

[mjd]

I'm affraid to put my services until I ensure that rescue of the failed booting procees is possible without overwrite everything by clean image.

I'm unaware of any manuals but I would install an alternate kernel and flick back and forth between them until I was happy.

And the question is, how to flick between them if I prefer to mount HDD to PC,  instead of serial console, and reconfigure.
What are the conf files where I poing out kernel of my choose.
Is there needed to execute some kind of grub-update or whatever analogical?

[evilbunny]

And the question is, how to flick between them if I prefer to mount HDD to PC,  instead of serial console, and reconfigure.

I haven't needed to do that, I just pick them on bootup from the boot menu

What are the conf files where I poing out kernel of my choose.

Most of them are on /boot or p6 partition, although the u-boot stuff is on some of the other 4 or 5 partitions

Is there needed to execute some kind of grub-update or whatever analogical?

Installing via apt or dpkg handles this.

[mjd]

Ok, thank you for interesting.

So far new kernel, 4.19-rc4, just works after install and for the future investigations I will buy serial console dongle.