I've emailed Rod Smith about this, as well, but haven't heard anything back yet. I'm hoping someone else has a fix.
I recently got a 27" iMac (the "late 2015" version) which has a 5k native resolution (5120x2880).
I've been wanting to install Linux on this machine, so I obtained rEFInd 0.10.1 and installed it successfully on the Recovery partition.
But when I first booted OS X using rEFInd, it boots into a lower resolution (3840 x 2160).
I rebooted into Recovery mode, used mountesp, and edited refind.conf to manually set the native resolution ("resolution 5120 2880"). But once I reboot, I get an error saying it can't set that screen mode, and then it boots once again with the incorrect resolution.
It appears rEFInd is incorrectly detecting what the default screen resolution should be on this version of the 27" iMac. Do you have any suggestions for how I might solve this problem?
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rEFInd does not adjust the screen resolution by default, so if you make no changes to refind.conf, you get what the firmware delivers. If you do set a screen resolution, of course, rEFInd tries to set it; however, the fact that a resolution is supported in an OS does not mean that it's supported in the firmware. On UEFI-based PCs, it's common to see the EFI driving the screen at 800x600, 1024x768, or some other relatively low resolution and to be unable to run it at 1366x768, 1920x1080, or whatever the monitor and OS use natively. You could be seeing something similar, at least in part.
If you can't get OS X itself to run at the monitor's native resolution, then that sounds like an OS X driver bug. That's not to say that rEFInd is not involved; if it works fine with rEFInd out of the picture but not with rEFInd in use, then clearly something is happening with rEFInd in the path to trigger the bug. I don't know what that would be, though, and I'd need to have an affected system in my hands to be able to investigate. If somebody with programming experience and such a system wants to give it a go, I'd be happy to offer advice, but this is complex enough that remote debugging will be extremely tedious, at best.
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Yeah, OS X works just fine and at the correct resolution, until I install rEFInd. I'll try to do some more troubleshooting when I can find the time, but for now it appears this is a showstopper for getting Linux on this particular machine.
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Willi, unfortunately no, I didn't get any further, and the computer is now on permanent loan to my mom, so I haven't had a chance to do any more work on the issue. I tried to find someone else who was running Linux on one of these iMacs and couldn't turn up much of anything.
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I've emailed Rod Smith about this, as well, but haven't heard anything back yet. I'm hoping someone else has a fix.
I recently got a 27" iMac (the "late 2015" version) which has a 5k native resolution (5120x2880).
I've been wanting to install Linux on this machine, so I obtained rEFInd 0.10.1 and installed it successfully on the Recovery partition.
But when I first booted OS X using rEFInd, it boots into a lower resolution (3840 x 2160).
I rebooted into Recovery mode, used mountesp, and edited refind.conf to manually set the native resolution ("resolution 5120 2880"). But once I reboot, I get an error saying it can't set that screen mode, and then it boots once again with the incorrect resolution.
It appears rEFInd is incorrectly detecting what the default screen resolution should be on this version of the 27" iMac. Do you have any suggestions for how I might solve this problem?
rEFInd does not adjust the screen resolution by default, so if you make no changes to
refind.conf, you get what the firmware delivers. If you do set a screen resolution, of course, rEFInd tries to set it; however, the fact that a resolution is supported in an OS does not mean that it's supported in the firmware. On UEFI-based PCs, it's common to see the EFI driving the screen at 800x600, 1024x768, or some other relatively low resolution and to be unable to run it at 1366x768, 1920x1080, or whatever the monitor and OS use natively. You could be seeing something similar, at least in part.If you can't get OS X itself to run at the monitor's native resolution, then that sounds like an OS X driver bug. That's not to say that rEFInd is not involved; if it works fine with rEFInd out of the picture but not with rEFInd in use, then clearly something is happening with rEFInd in the path to trigger the bug. I don't know what that would be, though, and I'd need to have an affected system in my hands to be able to investigate. If somebody with programming experience and such a system wants to give it a go, I'd be happy to offer advice, but this is complex enough that remote debugging will be extremely tedious, at best.
Hi Rod,
Yeah, OS X works just fine and at the correct resolution, until I install rEFInd. I'll try to do some more troubleshooting when I can find the time, but for now it appears this is a showstopper for getting Linux on this particular machine.
There are ways to dual-boot without rEFInd. You could use the older rEFIt and/or GRUB, for instance. I can't guarantee they'd do any better, though.
Hi Matthew,
I have exactly the same problem - did you find out anything about it ?
Willi, unfortunately no, I didn't get any further, and the computer is now on permanent loan to my mom, so I haven't had a chance to do any more work on the issue. I tried to find someone else who was running Linux on one of these iMacs and couldn't turn up much of anything.
Same issue 27" late 2015 imac 5k