On MacBookPro, Mid-2012 13″, A1278 details https://everymac.com/systems/apple/macbook_pro/specs/macbook-pro-core-i5-2.5-13-mid-2012-unibody-usb3-specs.html
Main SSD(upgraded from HDD few years before) is OSX 10.15.7.
I have replaced Optical drive with 2TB SSD (https://www.ifixit.com/Guide/Installing+MacBook+Pro+13-Inch+Unibody+Mid+2012+Dual+Hard+Drive/13787).
Installed kubuntu-22.04.5-desktop-amd64.iso on second ssd.
Reboot macbookpro
hold alt/option key, select EFI Boot boot, first in line, after that is original OSX disk
get screen “GNU GRUB version 2.06” with options
Ubuntu
Advanced options for Ubuntu
select “Ubuntu”
black screen, after that
error: failure reading sector 0xd4dbc0 from hd7.
error: you need to load the kernel first.
Press any key to continue...
it goes automatically (even if I do not press any key) to “GNU GRUB version 2.06”
In “Advanced options for Ubuntu” I have:
Ubuntu, with Linux 6.8.0-45-generic
Ubuntu, with Linux 6.8.0-45-generic (recovery mode)
Ubuntu, with Linux 6.8.0-40-generic
Ubuntu, with Linux 6.8.0-40-generic (recovery mode)
Every choice is same text , except 0x different
Loading Linux 6.8.0-40-generic ... (few second or up to 2-3 minutes on it)
error: failure reading sector 0x14baa00 from hd7.
Loading initial ramdisk ...
error: you need to load the kernel first.
Press any key to continue...
This person did everything as me and it is working fine, but not for me:
https://www.reddit.com/r/mac/comments/az2nrn/linux_dual_boot_on_2012_macbook_pro/
here is another opinion what to try:
The problem comes from Apple has restricted booting any other OS on a Mac computer that came with a built in DVD drive from only that DVD drive. An OS X installer can be booted from a USB port, from the USB thumb drive or DVD drive connected to a USB port but you can't boot Windows or Linux from the USB port.
So the only way to install Ubuntu, or any other OS than OS X. is to reinstalled the DVD drive and put the drive you want the other OS on in the main drive bay. Once it is installed you can move the drive to the optical bay.
https://discussions.apple.com/thread/5992651?sortBy=rank
Any ideas what to try next ?