Cannot boot from USB on iMac17,1 (27-inch 5k retina iMac running El Capitan)

[__PG__]

Hello all.

I'm trying to install Ubuntu on an iMac17,1 (27-inch 5k retina iMac) running El Captian.

At first I created a USB installer following these instructions : http://www.ubuntu.com/download/deskt...ick-on-mac-osx
I downloaded ubuntu-14.04.3-desktop-amd64.img and converted it to .iso.

When selecting the USB to boot from, it brings up the Grub 2.02~beta2-9ubuntu1.3 menu

*Try Ubuntu without installing
Install Unbuntu
OEM install (for manufacturers)
Check disc for defects

Once you select an option (either the first or second) the screen goes blank and nothing happens.

I have tried this with both a 4Gb an 8Gb drive.

I then tried this method : http://www.howtogeek.com/213396/how-...e-on-your-mac/
I used the downloaded iso file and attempted to boot from it. Here is the output:

SO path: (hd0,msdos1)/efi/boot/boot.iso
kernel path: /casper/vmlinuz.efi | ramdisc path: /casper/initrd.lz
boot folder : casper | boot parameters: file=/cdrom/preseed/ubuntu.seed


Loading Linux kernel..done


Loading initial RM disc... done


Attempting to boot the Linux distribution now...

At this point the process hangs and doesn't continue. I also tried a 4Gb and 8Gb key.

I repeated the process but I let the Mac Linux USB loader download Ubuntu 15.04 instead. This made no difference.

The third attempt used the UNetbooting process http://unetbootin.github.io/#other with my downloaded .iso file.
This produced the same results as the first method (i.e. black screen after the grub menu).

At this point I'm wondering what else to try. Would trying to boot off an external superdrive make any difference?
Do I need to disable csrutil before attempting to boot off the USB?

I note that there isn't much discussion about dual-booting iMacs here, the majority of the forum discussed dual-booting MacBooks (I have a dual-boot MacBook 5,3 with Ubuntu 14.04).

Is installing Ubuntu on an iMac more difficult than a MacBook?

Hoping someone can help.

[narender224]

Hello,
With Universal-USB-Installer-1.9.2.4 make USB pendrive as bootable.
and shutdown MAC, and power it on with holding OPTION button. boot with USB device

THanks
NSR

[__PG__]

That executable only works for Windows as far as I can tell.

I repeated the official Ubuntu USB instructions with csrutil disabled. It made no difference.
I also used the the other iso file ubuntu-14.04-desktop-amd64+mac.iso. This made no difference.

I burnt the original file ubuntu-14.04.3-desktop-amd64.iso onto a DVD and tried to boot from the USB superdrive. Before the grub menu appears, I get the following message

error : file '/boot' not found

The grub menu then appears, however once again a black screen occurs when attempting to boot.

I might try and use grub commands directly. When upgrading my MacBook Pro to OS X Mavericks it broke rEFIt/Grub so I had to manually boot using the grub command line.

I presume the following procedure will work

root=(hd0,xxx)
kernel /boot/vmlinuz-**** root=/dev/*** ro
initrd /boot/initrd-****
boot

I just need to find out where the /boot directory lies on the USB or DVD.

[__PG__]

Just looking at the default boot commands in Grub for *Try Ubuntu without installing when booting off cdrom

setparams 'Try Ubuntu without installing'

     set gfxpayload=keep
     linux            /casper/vmlinuz.efi file=/cdrom/preseed/ubuntu.seed boot=casper quiet splash --
     initrd           /casper/initird.iz

I might have to read up a bit more about GRUB2, it seems its a bit different to GRUB.

[luciano.x]

Maybe the problem is related to your video card.
Just try the kernel parameter 'nomodeset'.

Before hit try ubuntu, press key e
Replace quiet spash with nomodeset

Press Ctrl + x when done.

[__PG__]

I think you're right.
I think the issue is video related. I managed to get beyond the basic Grub2.0 screen by altering the gfxpayload command with a variety of screen resolutions. One of them worked however Grub failed to load as using 'Ctrl-X' didn't actually boot, rather it just passes 'x' as a Grub parameters F10 made it boot but Grub failed with a message along the lines of 'Command X' not found.

Next time I'll pass the right screen resolution to gfxpayload and only use F10. I'll also try nomodeset.

[charlie37]

Were you able to find a solution? I am running into the exact same issue. Have tried both CentOS and Ubuntu distros (with and without rEFInd) on this new iMac but only receive the same blank black screen. Thanks.

[__PG__]

Not yet.

I tried replacing quiet splash with nomodeset. It didn't work.
I added nomodeset after quiet splash. That didn't work.
I removed quiet splash.
I then tried various single screen resolutions with gfxpayload but they didn't work.
I got it working once...I'll keep at it.

[charlie37]

Thanks for the reply. Will keep checking this thread... If I can find some time to dig further into this and come up with a solution, I will update as well.

[__PG__]

It turns out that regardless of whatever gfxpayload options I provide, as long as enter an extraneous 'x' at the end of the grub command section, I will generate the subsequent menu 'error, command 'x' not found'.

So I had never had it working before.

I'm going to have a look at this : http://ubuntuforums.org/showthread.php?t=1743535

I've tried the 14.04 LTS USB and CDROM to boot on my old MacBook (which actually has Ubuntu installed) and it fails to boot there.
I get to the Ubuntu purple splash screen with five yellow dots, they all change colour, and then it hangs.
Evidently the message error : file '/boot' not found[COLOR=#000000]
means I'll have to figure out how to set it up via the GRUB2 command line.