Triple boot no longer working...

[billhughes]

For a long time I had a beautifully working quad-boot computer - then I had to mess around. :-)
I rebuilt /disk0 to update Windows to 64bit from 32. I did nothing to /disk1. Afterwards, refind can't boot to Ubuntu. Selecting its icon instead boot Windows. (I can boot all OSes by holding the Option key.)

Two drives, both GPT.

Drive 1 = Mac 10.10, Mac 10.11, Recovery 10.10, Windows 7 64bit
Drive 2 = /User/home, Ubuntu 15.04

Here is an edited df output:

/dev/disk0s1 /Volumes/EFI
/dev/disk0s2 /
/dev/disk0s4 /Volumes/El Capitan
/dev/disk0s5 /Volumes/Windows7

/dev/disk1s2 /Volumes/MacOSX
/dev/disk1s3 /Volumes/Ubuntu

I believe my problem is related to MBR/GPT problems, but I'm trying to work around it by using a boot stanza:

menuentry Linux {
icon EFI/refind/icons/os_linux.png
volume 42057142-D03E-47AA-8D9B-9C6F0B1D8F72
ostype Linux
loader vmlinuz
initrd initrd.img
options "ro root=/dev/sdb3 rootfstype=ext4"

This works until it's time to load the Light Display Manager. Then I get hung at a black screen.

Ideas? Suggestions?

Thanks!

[billhughes]

I gave up. Instead of having linux on a second internal drive, I moved it to the main boot drive with all the other OSes. MBR was then able to update properly.

[Roderick W. Smith]

Chances are you had been booting Linux in BIOS/CSM/legacy mode, probably using hybrid MBRs on both disks. This is a very delicate configuration, so it's not surprising that an OS update would cause problems.

In the long term, a better solution is to boot Linux in EFI mode. This is what your manual boot stanza did; however, you obviously ran into video problems with that approach. Chances are you could have worked around that by updating your video configuration or adding kernel boot parameters, although that's something that must be investigated on a machine-by-machine basis, and I have no database of solutions to such problems, so I couldn't help all that much.

For future reference, I recommend you read up on hybrid MBRs (see the link I provided earlier) and keep an eye open on any computer forums you frequent for information on EFI-mode booting of Linux on your specific Mac model.