[SOLVED] Pink screen after waking up from Suspend on iMac

[64BitAmoeba]

You have to disable screensaver in it's options not power management. That's what I found.

Yup! Disabled it in Light Locker, I think that's the name for the screensaver in Mint.

Hi all,
For me, the problem was booting in EFI mode. I have the exact iMac as 64BitAmoeba. In fact, I have two.

If I boot in EFI mode, no matter kernel 4.15 or 5.8.3, Linux Mint, Devuan or Linux from Scratch, Cinnamon, Mate, XFCE or KDE, booting from an HD partition or from a live CD, I will ALWAYS have the waviness upon waking from suspend and I NEVER have it while booting in legacy mode with grub with any of the above conditions.

I hope this information helps fix 64BitAmoeba's iMac and anyone else with this problem.

Jamie

Darn it! Now I know how to boot into legacy (install rEFInd, choose to boot legacy OS from whole disk). Issue is, it just boots me into a black screen with a forever-blinking cursor/underscore. (example). I got rEFIt installed and when I tried legacy boot, there, it told me, "No bootable device -- insert boot disk and press any key." In rEFInd, however, I noticed the legacy OS option disappeared. Still shows in rEFIt , though.

Does anyone know the cause of this and how to fix it? I was thinking maybe the boot manager is equating legacy OS with macOS or any other distro I previously installed. But I could be wrong.

[SMG]

Yup! Disabled it in Light Locker, I think that's the name for the screensaver in Mint.

In Cinnamon, the Screensaver app is called "Screensaver" and contains screensaver settings and lock settings.

[64BitAmoeba]

Yup! Disabled it in Light Locker, I think that's the name for the screensaver in Mint.

In Cinnamon, the Screensaver app is called "Screensaver" and contains screensaver settings and lock settings.

Sorry, was thinking about XFCE's. Correct, in Cinnamon, I disabled Screensaver completely, with no fix in sight.

I attached results of $ sudo lsblk -o name,size,fstype,parttype,label,mountpoint and boot-script-info for anyone interested in seeing if there is an issue with boot/EFI partitions or any of the sort. I am single-booting Linux as I replaced macOS with it.

Code: Select all

$ sudo lsblk -o name,size,fstype,parttype,label,mountpoint

NAME SIZE FSTYPE PARTTYPE LABEL MOUNTPOINT
sda 232.9G
├─sda1 512M vfat c12a7328-f81f-11d2-ba4b-00a0c93ec93b /boot/efi
└─sda2 232.4G ext4 0fc63daf-8483-4772-8e79-3d69d8477de4 /
sr0

Code: Select all

Boot Info Script 0.78      [09 October 2019]

Identifying MBRs...
Computing Partition Table of /dev/sda...
Searching sda1 for information... 
Searching sda2 for information... 
                 Boot Info Script 0.78      [09 October 2019]


============================= Boot Info Summary: ===============================

 => No boot loader is installed in the MBR of /dev/sda.

sda1: __________________________________________________________________________

    File system:       vfat
    Boot sector type:  FAT32
    Boot sector info:  No errors found in the Boot Parameter Block.
    Operating System:  
    Boot files:        /efi/BOOT/fbx64.efi /efi/BOOT/mmx64.efi 
                       /efi/refind/refind_x64.efi /efi/ubuntu/grubx64.efi 
                       /efi/ubuntu/mmx64.efi /efi/ubuntu/shimx64.efi 
                       /efi/ubuntu/grub.cfg 
                       /efi/refind/drivers_x64/ext4_x64.efi

sda2: __________________________________________________________________________

    File system:       ext4
    Boot sector type:  -
    Boot sector info: 
    Operating System:  Linux Mint 20
    Boot files:        /boot/grub/grub.cfg /etc/fstab

============================ Drive/Partition Info: =============================

Drive: sda _____________________________________________________________________
Disk /dev/sda: 232.91 GiB, 250059350016 bytes, 488397168 sectors
Disk model: Hitachi HDP72502
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes

Partition  Boot  Start Sector    End Sector  # of Sectors  Id System

/dev/sda1                   1     1,050,623     1,050,623  ee GPT
/dev/sda2    *      1,050,624   488,396,799   487,346,176  83 Linux


GUID Partition Table detected.

Partition  Attrs   Start Sector    End Sector  # of Sectors System
/dev/sda1                 2,048     1,050,623     1,048,576 EFI System partition
/dev/sda2             1,050,624   488,396,799   487,346,176 Data partition (Linux)

Attributes: R=Required, N=No Block IO, B=Legacy BIOS Bootable, +=More bits set

"blkid" output: ________________________________________________________________

Device           UUID                                   TYPE       LABEL

/dev/sda1        D9CC-BDB9                              vfat       
/dev/sda2        d84f06b6-2ed5-496d-8e4f-cd0d76b10e0a   ext4       

========================= "ls -l /dev/disk/by-id" output: ======================

total 0
lrwxrwxrwx 1 root root  9 Nov 20 19:59 ata-Hitachi_HDP725025GLA380_GEK260RS28VMTA -> ../../sda
lrwxrwxrwx 1 root root 10 Nov 20 19:59 ata-Hitachi_HDP725025GLA380_GEK260RS28VMTA-part1 -> ../../sda1
lrwxrwxrwx 1 root root 10 Nov 20 19:59 ata-Hitachi_HDP725025GLA380_GEK260RS28VMTA-part2 -> ../../sda2
lrwxrwxrwx 1 root root  9 Nov 20 19:59 ata-OPTIARC_DVD_RW_AD-5630A -> ../../sr0
lrwxrwxrwx 1 root root  9 Nov 20 19:59 wwn-0x5000cca355e035f9 -> ../../sda
lrwxrwxrwx 1 root root 10 Nov 20 19:59 wwn-0x5000cca355e035f9-part1 -> ../../sda1
lrwxrwxrwx 1 root root 10 Nov 20 19:59 wwn-0x5000cca355e035f9-part2 -> ../../sda2

================================ Mount points: =================================

Device           Mount_Point              Type       Options

/dev/sda1        /boot/efi                vfat       (rw,relatime,fmask=0077,dmask=0077,codepage=437,iocharset=iso8859-1,shortname=mixed,errors=remount-ro)
/dev/sda2        /                        ext4       (rw,relatime,errors=remount-ro)


========================== sda1/efi/ubuntu/grub.cfg: ===========================

--------------------------------------------------------------------------------
search.fs_uuid d84f06b6-2ed5-496d-8e4f-cd0d76b10e0a root hd0,gpt2 
set prefix=($root)'/boot/grub'
configfile $prefix/grub.cfg
--------------------------------------------------------------------------------

=========================== sda2/boot/grub/grub.cfg: ===========================

--------------------------------------------------------------------------------
#
# DO NOT EDIT THIS FILE
#
# It is automatically generated by grub-mkconfig using templates
# from /etc/grub.d and settings from /etc/default/grub
#

### BEGIN /etc/grub.d/00_header ###
if [ -s $prefix/grubenv ]; then
  set have_grubenv=true
  load_env
fi
if [ "${initrdfail}" = 2 ]; then
   set initrdfail=
elif [ "${initrdfail}" = 1 ]; then
   set next_entry="${prev_entry}"
   set prev_entry=
   save_env prev_entry
   if [ "${next_entry}" ]; then
      set initrdfail=2
   fi
fi
if [ "${next_entry}" ] ; then
   set default="${next_entry}"
   set next_entry=
   save_env next_entry
   set boot_once=true
else
   set default="0"
fi

if [ x"${feature_menuentry_id}" = xy ]; then
  menuentry_id_option="--id"
else
  menuentry_id_option=""
fi

export menuentry_id_option

if [ "${prev_saved_entry}" ]; then
  set saved_entry="${prev_saved_entry}"
  save_env saved_entry
  set prev_saved_entry=
  save_env prev_saved_entry
  set boot_once=true
fi

function savedefault {
  if [ -z "${boot_once}" ]; then
    saved_entry="${chosen}"
    save_env saved_entry
  fi
}
function initrdfail {
    if [ -n "${have_grubenv}" ]; then if [ -n "${partuuid}" ]; then
      if [ -z "${initrdfail}" ]; then
        set initrdfail=1
        if [ -n "${boot_once}" ]; then
          set prev_entry="${default}"
          save_env prev_entry
        fi
      fi
      save_env initrdfail
    fi; fi
}
function recordfail {
  set recordfail=1
  if [ -n "${have_grubenv}" ]; then if [ -z "${boot_once}" ]; then save_env recordfail; fi; fi
}
function load_video {
  if [ x$feature_all_video_module = xy ]; then
    insmod all_video
  else
    insmod efi_gop
    insmod efi_uga
    insmod ieee1275_fb
    insmod vbe
    insmod vga
    insmod video_bochs
    insmod video_cirrus
  fi
}

if [ x$feature_default_font_path = xy ] ; then
   font=unicode
else
insmod part_gpt
insmod ext2
set root='hd0,gpt2'
if [ x$feature_platform_search_hint = xy ]; then
  search --no-floppy --fs-uuid --set=root --hint-bios=hd0,gpt2 --hint-efi=hd0,gpt2 --hint-baremetal=ahci0,gpt2  d84f06b6-2ed5-496d-8e4f-cd0d76b10e0a
else
  search --no-floppy --fs-uuid --set=root d84f06b6-2ed5-496d-8e4f-cd0d76b10e0a
fi
    font="/usr/share/grub/unicode.pf2"
fi

if loadfont $font ; then
  set gfxmode=auto
  load_video
  insmod gfxterm
  set locale_dir=$prefix/locale
  set lang=en_US
  insmod gettext
fi
terminal_output gfxterm
if [ "${recordfail}" = 1 ] ; then
  set timeout=30
else
  if [ x$feature_timeout_style = xy ] ; then
    set timeout_style=hidden
    set timeout=0
  # Fallback hidden-timeout code in case the timeout_style feature is
  # unavailable.
  elif sleep --interruptible 0 ; then
    set timeout=0
  fi
fi
### END /etc/grub.d/00_header ###

### BEGIN /etc/grub.d/05_debian_theme ###
set menu_color_normal=white/black
set menu_color_highlight=black/light-gray
### END /etc/grub.d/05_debian_theme ###

### BEGIN /etc/grub.d/10_linux ###
function gfxmode {
	set gfxpayload="${1}"
	if [ "${1}" = "keep" ]; then
		set vt_handoff=vt.handoff=7
	else
		set vt_handoff=
	fi
}
if [ "${recordfail}" != 1 ]; then
  if [ -e ${prefix}/gfxblacklist.txt ]; then
    if hwmatch ${prefix}/gfxblacklist.txt 3; then
      if [ ${match} = 0 ]; then
        set linux_gfx_mode=keep
      else
        set linux_gfx_mode=text
      fi
    else
      set linux_gfx_mode=text
    fi
  else
    set linux_gfx_mode=keep
  fi
else
  set linux_gfx_mode=text
fi
export linux_gfx_mode
menuentry 'Linux Mint 20 Cinnamon' --class linuxmint --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-simple-d84f06b6-2ed5-496d-8e4f-cd0d76b10e0a' {
	recordfail
	load_video
	gfxmode $linux_gfx_mode
	insmod gzio
	if [ x$grub_platform = xxen ]; then insmod xzio; insmod lzopio; fi
	insmod part_gpt
	insmod ext2
	set root='hd0,gpt2'
	if [ x$feature_platform_search_hint = xy ]; then
	  search --no-floppy --fs-uuid --set=root --hint-bios=hd0,gpt2 --hint-efi=hd0,gpt2 --hint-baremetal=ahci0,gpt2  d84f06b6-2ed5-496d-8e4f-cd0d76b10e0a
	else
	  search --no-floppy --fs-uuid --set=root d84f06b6-2ed5-496d-8e4f-cd0d76b10e0a
	fi
	linux	/boot/vmlinuz-5.4.0-26-generic root=UUID=d84f06b6-2ed5-496d-8e4f-cd0d76b10e0a ro  quiet splash 
	initrd	/boot/initrd.img-5.4.0-26-generic
}
submenu 'Advanced options for Linux Mint 20 Cinnamon' $menuentry_id_option 'gnulinux-advanced-d84f06b6-2ed5-496d-8e4f-cd0d76b10e0a' {
	menuentry 'Linux Mint 20 Cinnamon, with Linux 5.4.0-26-generic' --class linuxmint --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-5.4.0-26-generic-advanced-d84f06b6-2ed5-496d-8e4f-cd0d76b10e0a' {
		recordfail
		load_video
		gfxmode $linux_gfx_mode
		insmod gzio
		if [ x$grub_platform = xxen ]; then insmod xzio; insmod lzopio; fi
		insmod part_gpt
		insmod ext2
		set root='hd0,gpt2'
		if [ x$feature_platform_search_hint = xy ]; then
		  search --no-floppy --fs-uuid --set=root --hint-bios=hd0,gpt2 --hint-efi=hd0,gpt2 --hint-baremetal=ahci0,gpt2  d84f06b6-2ed5-496d-8e4f-cd0d76b10e0a
		else
		  search --no-floppy --fs-uuid --set=root d84f06b6-2ed5-496d-8e4f-cd0d76b10e0a
		fi
		echo	'Loading Linux 5.4.0-26-generic ...'
		linux	/boot/vmlinuz-5.4.0-26-generic root=UUID=d84f06b6-2ed5-496d-8e4f-cd0d76b10e0a ro  quiet splash 
		echo	'Loading initial ramdisk ...'
		initrd	/boot/initrd.img-5.4.0-26-generic
	}
	menuentry 'Linux Mint 20 Cinnamon, with Linux 5.4.0-26-generic (recovery mode)' --class linuxmint --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-5.4.0-26-generic-recovery-d84f06b6-2ed5-496d-8e4f-cd0d76b10e0a' {
		recordfail
		load_video
		insmod gzio
		if [ x$grub_platform = xxen ]; then insmod xzio; insmod lzopio; fi
		insmod part_gpt
		insmod ext2
		set root='hd0,gpt2'
		if [ x$feature_platform_search_hint = xy ]; then
		  search --no-floppy --fs-uuid --set=root --hint-bios=hd0,gpt2 --hint-efi=hd0,gpt2 --hint-baremetal=ahci0,gpt2  d84f06b6-2ed5-496d-8e4f-cd0d76b10e0a
		else
		  search --no-floppy --fs-uuid --set=root d84f06b6-2ed5-496d-8e4f-cd0d76b10e0a
		fi
		echo	'Loading Linux 5.4.0-26-generic ...'
		linux	/boot/vmlinuz-5.4.0-26-generic root=UUID=d84f06b6-2ed5-496d-8e4f-cd0d76b10e0a ro recovery nomodeset 
		echo	'Loading initial ramdisk ...'
		initrd	/boot/initrd.img-5.4.0-26-generic
	}
}

### END /etc/grub.d/10_linux ###

### BEGIN /etc/grub.d/10_linux_zfs ###
### END /etc/grub.d/10_linux_zfs ###

### BEGIN /etc/grub.d/20_linux_xen ###

### END /etc/grub.d/20_linux_xen ###

### BEGIN /etc/grub.d/30_os-prober ###
### END /etc/grub.d/30_os-prober ###

### BEGIN /etc/grub.d/30_uefi-firmware ###
### END /etc/grub.d/30_uefi-firmware ###

### BEGIN /etc/grub.d/40_custom ###
# This file provides an easy way to add custom menu entries.  Simply type the
# menu entries you want to add after this comment.  Be careful not to change
# the 'exec tail' line above.
### END /etc/grub.d/40_custom ###

### BEGIN /etc/grub.d/41_custom ###
if [ -f  ${config_directory}/custom.cfg ]; then
  source ${config_directory}/custom.cfg
elif [ -z "${config_directory}" -a -f  $prefix/custom.cfg ]; then
  source $prefix/custom.cfg;
fi
### END /etc/grub.d/41_custom ###
--------------------------------------------------------------------------------

=============================== sda2/etc/fstab: ================================

--------------------------------------------------------------------------------
# /etc/fstab: static file system information.
#
# Use 'blkid' to print the universally unique identifier for a
# device; this may be used with UUID= as a more robust way to name devices
# that works even if disks are added and removed. See fstab(5).
#
# <file system> <mount point>   <type>  <options>       <dump>  <pass>
# / was on /dev/sda2 during installation
UUID=d84f06b6-2ed5-496d-8e4f-cd0d76b10e0a /               ext4    errors=remount-ro 0       1
# /boot/efi was on /dev/sda1 during installation
UUID=D9CC-BDB9  /boot/efi       vfat    umask=0077      0       1
/swapfile                                 none            swap    sw              0       0
--------------------------------------------------------------------------------

=================== sda2: Location of files loaded by Grub: ====================

           GiB - GB             File                                 Fragment(s)

 152.781871796 = 164.048285696  boot/grub/grub.cfg                             1
   4.884544373 = 5.244739584    boot/vmlinuz                                   2
   4.884544373 = 5.244739584    boot/vmlinuz-5.4.0-26-generic                  2
 153.102092743 = 164.392120320  boot/initrd.img                                3
 153.102092743 = 164.392120320  boot/initrd.img-5.4.0-26-generic               3
 153.102092743 = 164.392120320  boot/initrd.img.old    

Thanks again everybody for your invaluable help, means a whole lot, even if this bad boy won't make it to sleep

[SMG]

Darn it! Now I know how to boot into legacy (install rEFInd, choose to boot legacy OS from whole disk). Issue is, it just boots me into a black screen with a forever-blinking cursor/underscore. (example). I got rEFIt installed and when I tried legacy boot, there, it told me, "No bootable device -- insert boot disk and press any key." In rEFInd, however, I noticed the legacy OS option disappeared. Still shows in rEFIt , though.

Does anyone know the cause of this and how to fix it? I was thinking maybe the boot manager is equating legacy OS with macOS or any other distro I previously installed. But I could be wrong.

Maybe something in this thread Apple iMac 17-Inch "Core 2 Duo" installation (linux Mint MATE 19.3) will help. The words highlighted in pink on that thread are ones I used for searching this forum.

[64BitAmoeba]

Darn it! Now I know how to boot into legacy (install rEFInd, choose to boot legacy OS from whole disk). Issue is, it just boots me into a black screen with a forever-blinking cursor/underscore. (example). I got rEFIt installed and when I tried legacy boot, there, it told me, "No bootable device -- insert boot disk and press any key." In rEFInd, however, I noticed the legacy OS option disappeared. Still shows in rEFIt , though.

Does anyone know the cause of this and how to fix it? I was thinking maybe the boot manager is equating legacy OS with macOS or any other distro I previously installed. But I could be wrong.

Maybe something in this thread Apple iMac 17-Inch "Core 2 Duo" installation (linux Mint MATE 19.3) will help. The words highlighted in pink on that thread are ones I used for searching this forum.

I tried the advice on blessing the disk, again, it booted me into this infamous error: "No bootable device -- insert boot disk and press any key." Through rEFInd, I found something interesting: that message actually pops up when the device is trying to boot legacy. The EFI installation, however, is still intact when I booted EFI into the device.

I figured that if I can't boot legacy, then that means I didn't install via legacy in the first place. I'm not knowledgeable about how I can identify if a live environment of Linux Mint is booted EFI or legacy, but I have experience with Solus OS. I burned my ISO on a USB drive and chose MBR rather than GPT in Rufus. The issue is, when I land on this window, you can see that the option "Bootloader installation mandatory with UEFI" is grayed out and checked. No way to uncheck it, a sign that this is an EFI installation at progress.



At this point, I'm trying to solve the puzzle of entering legacy mode for the installation. I attempted booting via rEFInd. The only working options are all EFI. Choices like "boot Linux legacy from whole disk" simply don't work. Booting into kernel or /boot/kernel also don't work. They spit out that "no bootable device -- insert boot disk and press any key" error.

On the other hand, jamiemint suggested a great solution: using a DVD. It works well. For some reason, LiveDVD only boots legacy (at least on my iMac), and my iMac doesn't have sleep problems anymore. So if anyone has a spare DVD and they can burn this ISO on it, feel free to do so and hold option just the "C" key while the disk is in to boot into it after powering on your iMac. But the last Mac computer shipped with an optical drive was in June 2012, so it'd be awesome if we can tackle this issue with thumb drives as well, fingers crossed

[SMG]

On the other hand, jamiemint suggested a great solution: using a DVD. It works well. For some reason, LiveDVD only boots legacy (at least on my iMac), and my iMac doesn't have sleep problems anymore.

Glad to hear the issue is resolved. If you edit the first post in this thread to add [SOLVED] that will alert others with a similar issue this might be a helpful thread to read.

[chinarut]

On the other hand, jamiemint suggested a great solution: using a DVD. It works well. For some reason, LiveDVD only boots legacy (at least on my iMac), and my iMac doesn't have sleep problems anymore. So if anyone has a spare DVD and they can burn this ISO on it, feel free to do so and hold option just the "C" key while the disk is in to boot into it after powering on your iMac.

OMG! thank you @64BitAmoeba for doing all this detective work!!! I was trying to figure this out when I moved my dad to Ubuntu back in June (2020) and this was driving me nuts and had to put it down and picked this up again this past week. I installed xscreensaver and couldn't bear the thought of the poor machine running 24/7 and found your thread.

I booted 20.04 from DVD and sure enough it sleeps! It's more of a proof of concept as Firefox doesn't even launch off the LiveCD correctly (not to mention the insanely long boot time even if you skip verifying media...). I'm just happy to see Ubuntu on this iMac be able to sleep.

Now that we've verified this can be addressed through software, how do we work towards a permanent solution/patch?

Can we provide more information to Ubuntu developers as to what is specific to our machine when we try to sleep booting off a local 20.04.1 install?

We have an iMac early or mid-2008 (Core 2 Duo) as well.

[64BitAmoeba]

Thank you for your kind words. Booting from LiveDVD can be unbearably slow. The goal, however, is to force a legacy boot installation on your HDD/SSD so that your iMac can sleep correctly. So, if you want to run Ubuntu faster, I'd recommend backing up your files and installing Ubuntu on your HDD or SSD.

I tried submitting a bug report to Launchpad. Nothing came out of it, so I simply closed it. It seems like a universal problem with the Linux kernel (this happens in every single distro I tried), and I'm only a novice, but I can definitely get in touch with kernel maintainers and let them know about this problem. And I'll keep this thread updated with any response and updates. I'm not sure what the problem even is; why does iMac sleep properly only in a legacy installation as opposed to UEFI installation? Something is wrong.

[64BitAmoeba]

Got an update from Radeon/AMDGPU drivers maintainers. Looks like this is hopeless. These iMacs are an anomaly when it comes to standard protocols. They did recommend me to use a tool called radeonreg (https://cgit.freedesktop.org/~agd5f/radeontool), but I don't know how to use this tool at all. All I was told was that this tool can dump display registers preceding and succeeding suspending the iMac, then see the difference in the output to 1. determine which registers differ and 2. use that to pin down the specific culprit registers.

[chinarut]

hey thanks for doing more sleuthing & discovering that tool!

When I find cycles to play with radeonreg & figure out how to identify the registers that differ, I'll be sure to post back here.

[zer0aster]

I have seen the same effect after waking from suspend on Linuxmint, ElementaryOS and Opensuse Leap. However, Tails gets it right. So whatever suspend state it goes to, when it wakes, all is well.

Hope that gives someone a clue!

[karlchen]

Hello, zer0aster.

Welcome to the Linux Mint forum.

Honestly, I doubt that you post will give anyone a clue how to resolve the problem, which 64BitAmoeba had reported in November 2020 .
Hardly anyone will know what precisely Tails does differently from the other mentioned Linux distributions.

The really weird thing about this whole thread, however, is that 64BitAmoeba marked it as [solved] on November 23rd, 2020.
Yet, the 2 posts, which 64BitAmoeba submitted after that date in January & February 2021 suggest that the problem has not been solved at all.
Hm. I do not have to understand, I guess.

So, zer0aster, you might feel free to bombard us with as many relevant technical details, as you can. Maybe in August 2021 it will then be possible to identify the culprit and to resolve the issue. Maybe.

Regards,
Karl

[iiegn]

A few weeks ago, Firefox 78 ESR reached its end-of-life for my aged iMac 7,1 (OS X 10.11 had stopped long before) and it seemed like a waste of still functioning hardware to just leave it be. After installing a current Ubuntu 20.04 LTS, the iMac started with all things functioning fine (wlan, bluetooth, display+graphics, etc.) - all but resume from suspend: after resume, I ended up with something very similar to the initial screenshot, a colour and slightly pixel distorted screen with a pink tint but a working computer.
Quite a bit of searching often brought me back to this thread - and in the end, so it seems, enough bits and pieces are mentioned to actually solve the puzzle - well, at least, mine.

For my iMac, the solution was indeed to start (rEFInd and then boot) in legacy mode, which, I believe, is suggested at some point in this thread. The biggest obstacle then was to get legacy mode up and running. I haven't cleaned out all my OS X data and need to dual-boot. Hence, I need rEFInd and then a possibility to chainload into legacy.

Since my partition configuration didn't allow for the 'usual' embedding of GRUB in the existing partition schema, I followed https://superuser.com/a/1213967, reduced my last partition (which was the SWAP partition) a tiny bit, and created a BIOS Boot partition:

[...]
To create those using gdisk:

o: Create new GPT scheme
n, 1, accept default, +1M, EF02: Create BIOS Boot partition
n, 2, accept default, +1G, 8200: Create swap partition (1 GB)
n, 3, accept default, accept default, accept default: Create root partition
w: Write to disk and exit

Then, I installed GRUB like this

Code: Select all

grub-install --target=i386-pc --recheck --boot-directory=/boot/ /dev/sda

So, I am posting this here to maybe help some people in some cases with their 'pink screen after waking up from suspend on iMac'.

For reference, my configuration:

Code: Select all

System:    Kernel: 5.11.0-37-generic x86_64 bits: 64 compiler: N/A Desktop: MATE 1.24.0 
           Distro: Ubuntu 20.04.3 LTS (Focal Fossa) 
Machine:   Type: Desktop System: Apple product: iMac7,1 v: 1.0 serial: <filter> 
           Mobo: Apple model: Mac-F4238CC8 v: PVT serial: <filter> BIOS: Apple 
           v: IM71.88Z.007A.B03.0803051705 date: 03/05/08 
CPU:       Topology: Dual Core model: Intel Core2 Duo T7700 bits: 64 type: MCP arch: Core Merom 
           rev: B L2 cache: 4096 KiB 
           flags: lm nx pae sse sse2 sse3 ssse3 vmx bogomips: 9575 
           Speed: 1217 MHz min/max: 800/2400 MHz Core speeds (MHz): 1: 946 2: 1168 
Graphics:  Device-1: AMD RV630/M76 [Mobility Radeon HD 2600 XT/2700] vendor: Apple iMac 7 1 
           driver: radeon v: kernel bus ID: 01:00.0 
           Display: x11 server: X.Org 1.20.11 driver: ati,radeon unloaded: fbdev,modesetting,vesa 
           resolution: 1680x1050~60Hz 
           OpenGL: renderer: AMD RV630 (DRM 2.50.0 / 5.11.0-37-generic LLVM 12.0.0) 
           v: 3.3 Mesa 21.0.3 direct render: Yes 

Useful links:
* http://www.rodsbooks.com/refind/
* https://www.rodsbooks.com/gdisk/hybrid.html
* https://wiki.archlinux.org/title/GRUB
* https://wiki.debian.org/IntelMac/BootLoader