My question is, how do I add a (properly-booting) Ubuntu volume to High Sierra's "Startup Disk" Menu?

Running MacOS High Sierra, Windows 10 (Legacy, not EFI), and Ubuntu 18.04 (triple-booting on a 2009 MacPro 4,1 w/ firmware upgrade to 5,1). I installed Ubuntu after Windows using the procedure in this link. I have a second EFI partition for Ubuntu (scroll down for output from diskutil list). I've placed / renamed the boot files so that all three operating systems boot normally using Apple's Startup Manager (holding ALT during bootup) - see this link and this link for guidelines:

Apple Boot Manager - Natively triple-booting

However, I cannot select Ubuntu as a bootup option through the "Startup Disk" tool in High Sierra. Initially, the "Startup Disk" menu had no entry for Ubuntu. Then, I followed these steps to create a dummy mach_kernel file and place a SystemVersion.plist from in /System/Library/CoreServices/ my Ubuntu EFI partition. Now, Ubuntu appears in my "Startup Disk" menu, however I cannot select it. "Startup Disk" fails to select Ubuntu, and says, "Running bless to place boot files failed."After creating dummy mach_kernel, Startup Disk shows Ubuntu but still fails to boot Selecting "Ubuntu" causes this error

Currently, I'm working around this by using the following bless command to boot directly into Ubuntu from High Sierra (only works if csrutil is disabled in Recovery):

sudo bless --device /dev/disk0s5 --setboot --nextonly && sudo reboot

It works for now, but I would appreciate any insights on how to add Ubuntu to High Sierra's "Startup Disk." Thanks!

Output of diskutil list:

/dev/disk0 (internal, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *2.0 TB     disk0
   1:                        EFI EFI                     209.7 MB   disk0s1
   2:                  Apple_HFS Macintosh HD            1.5 TB     disk0s2
   3:                 Apple_Boot Recovery HD             650.0 MB   disk0s3
   4:       Microsoft Basic Data BOOTCAMP                290.3 GB   disk0s4
   5:                  Apple_HFS Ubuntu                  200.3 MB   disk0s5
   6:                 Linux Swap                         8.0 GB     disk0s6
   7:           Linux Filesystem                         201.5 GB   disk0s7
  • 1
    I can't hope to provide an answer on this, though I have a similar machine... but I often wonder why it wouldn't be simpler to just run all this in VMs. A Mac Pro has sufficient raw power, even allowing for its age, that a VM would just seem... easier.
    – Tetsujin
    Aug 2, 2018 at 19:29
  • @Tetsujin, Thanks! I set up VirtualBox, but encountered some difficulties setting up a virtual hard drive based on my existing native installation. I'm very happy with the speed of a native installation (now that it boots) compared to a VM - just a question of ease of transit between the different operating systems.
    – vrl2
    Aug 2, 2018 at 19:50


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