Score:0

Grub2 settings to boot on 2018 (T2) mac book pro (Ubuntu 20.04, external hardrive)

ru flag

I have a 2018 mac book pro (intel x86_64, Intel Iris Plus Graphics 655) that I'm trying to boot into Ubuntu 20.04 on an external hardrive (128gb USB stick). I have ubuntu and grub2 successfully installed on the USB stick (not a live usb! full OS and bootloader install) and can boot to multiple other PC's that do not have grub2 or any other linux distros installed. The usb can boot on UEFI-only systems and gdisk reports that there is a valid GPT partition table on the drive. gdisk also indicates that there is a "protective MBR" partition table on the drive, which I know nothing about or how it affects the GPT table.

When I try to boot on my mac book pro all I get is a black screen. I have my secure boot setting set to "no security" and I've allowed booting from external or removable media.

I'm assuming that the lack of a grub menu indicates that with its current configuration, grub is incompatible with my mac book's firmware. What how can I configure grub to play nice with the mac firmware so I can boot ubuntu?

oldfred avatar
cn flag
Do not know Mac, but did you install in UEFI boot mode to gpt partitioned drive? Ubuntu defaults to install grub to first or internal drive, so more difficult to install in UEFI mode to external drives. You typically have to change settings or do a grub repair install afterwards for any second or external drive install. Issue with several work arounds: https://bugs.launchpad.net/ubuntu/+source/ubiquity/+bug/1396379 & https://askubuntu.com/questions/1250199/move-bootloader-or-remove-efi-partition-in-second-drive or what video chip do you have? You may need nomodeset boot parameter.
ru flag
When i installed ubuntu it was on a computer with boot settings to use BIOS/ MBR OR UEFI/ GPT, whichever was detected. And the boot loader was loaded into the USB because i removed all other storage devices, so the only place grub could go was onto the USB. I've updated my question to include additional details.
oldfred avatar
cn flag
If when installed, it only saw Ubuntu, you do not get grub menu by default. With PC, you have to press escape key perhaps several times from Vendor screen till grub normally shows menu. Not sure what key you use with a Mac. The protective MBR with gpt is for old partition tools to see that drive has partitioning. The MBR then has one entry saying drive is gpt partitioned. Almost all tools now support gpt, so less of an issue.
ru flag
Ok i see, so should i try the nomodeset boot parameter? All of the computers I've booted the live USB, including the one ubuntu was installed to the USB on, have had discrete graphics hardware. I haven't been able to test booting the USB on a computer with integrated graphics other than the mac book, which like i said, hangs on a black screen. Ive also heard people talk about using noatime or something like that? I wish i could be more specific but grub is new territory for me.
oldfred avatar
cn flag
Try nomodeset as boot parameter. Normally not needed with Intel, but some very new Intel video chips need a boot parameter. The noatime is a setting for fstab and mounting a drive. Usually I use noatime for SSD and relatime for HDD. See `man mount` for more info on noatime & other mount parameters. New systems may work better with newest Ubuntu or newest kernel.
mangohost

Post an answer

Most people don’t grasp that asking a lot of questions unlocks learning and improves interpersonal bonding. In Alison’s studies, for example, though people could accurately recall how many questions had been asked in their conversations, they didn’t intuit the link between questions and liking. Across four studies, in which participants were engaged in conversations themselves or read transcripts of others’ conversations, people tended not to realize that question asking would influence—or had influenced—the level of amity between the conversationalists.