Forced convert to Linux Mint on a high dpi iMac

[fox]

I've been doing a lot of buying and selling of my Mac equipment lately in order to get some more recent stuff, and my most recent purchase was a 27" late 2015 iMac, which I got by trading in an older one. This computer is really different though, because of its 5K resolution (5120x2880). I hadn't realized at the time that this might cause problems with Linux distros, but it does. I wanted to run Ubuntu 17.04 on it, but no dice - neither an existing installation or a live installation disk would boot.  I would always end up with a dark purple screen. I searched for solutions and came up with a few posts suggesting a change to the grub boot parameters (adding nointremap or nomodeset or acpi=off) would fix this, but it didn't. I tried Ubuntu 16.04 and got the same result, so I then tried some other distros as well as the Ubuntu 17.10 beta 2. The latest Fedora wouldn't boot at all, nor would Elementary. Clonezilla would boot to the first screen and then freeze. Ubuntu 17.10 beta and OpenSuse Leap would boot, but they would take 5 minutes to do so. I didn't try installing OpenSuse, but I did Ubuntu. It did install, and changing its grub boot parameter would allow it to boot up, but again taking many minutes. When it did boot up, network-manager would not connect to the internet with either ethernet or wifi.

I don't know if it matters, but this iMac is the mid-level one with the 3.3 ghz i5 and a Radeon R9 M395 video card; maybe that particular video card is more problematic than the default. At this point I was ready to tear my hair out, but I tried one more distro: Linux Mint Cinnamon 18.2. Changing the boot parameter to nointremap, it booted right up, installed OK, and the installation booted up normally once I permanently added nointremap to the boot sequence! I haven't been interested in either Linux Mint or the Cinnamon desktop for a long time, but I figured I'd better make this to my liking if it's the only thing that would work properly. I spent a lot of time customizing it to my liking, which basically means changing icons and making the panel look like Ubuntu Unity. Turns out that you can do this by adding a vertical bar on the left side of the monitor and pinning my most used applications to it. I can live with this! My only complaint is the lack of fine-grain magnification adjustment in Cinnamon; the only choices are default or 2x magnification for high dpi. (Ubuntu allows you to magnify to tenths.) But the 2x works for me.

Even though I'm happy with Mint, I'm still bugged about not being able to install Ubuntu. Others have been able to get Ubuntu to boot on a 5k iMac, so why couldn't I (unless it's the specific video card)? Mint 18.2 is a derivative of Ubuntu 16.04, so why should it boot so easily when 16.04 wouldn't boot at all? What is different about 17.10 beta that it can boot (though with a lot of stalling) when the previous version cannot? Also, I don't like the fact that I can't boot a Clonezilla disk on this because I use it a lot. I'm wondering what I can try to get Ubuntu and Clonezilla to boot from a live USB, and install in the case of Ubuntu. Might it work if I simply copied all of the grub boot parameters in Mint and use them with Ubuntu? I might try that next, but any suggestions would be welcome.

[Jason]

Probably not that helpful but there are Linux Radeon drivers you can download. With a resolution that high, default drivers probably won't cut it. You may have been lucky enough in Linux Mint that it picked up and installed an appropriate Radeon driver but I'm not sure.

[fox]

Actually, I don't think Mint did because when I looked at drivers, it didn't register anything other than Intel Microcode. At any rate, assuming I found the appropriate one and downloaded it, how would I use it? Is this something I can deal with on the installer or something I have to add after a distro is installed? I'm not sure the latter would help since I can't even boot up a Ubuntu installer other than the 17.10 beta and the network wasn't functioning in the 17.10 beta.

Incidentally, even Mint doesn't give me the full resolution, though it did give me something halfway between 2560x1440 and full 5k resolution. This is a known problem with Linux on 5k and the resolution I get is quite good.

[Jason]

Actually, I don't think Mint did because when I looked at drivers, it didn't register anything other than Intel Microcode. At any rate, assuming I found the appropriate one and downloaded it, how would I use it? Is this something I can deal with on the installer or something I have to add after a distro is installed?

You'd have to add it after installation. If your network isn't working though, I doubt a video driver will be much use to you except that maybe it would help in troubleshooting your network problem.

I just did a quick search and found that there were Linux drivers for that card. They were just for Fedora, openSUSE and Ubuntu and older versions at that, but there were installation instructions with the download. I just searched "Radeon R9 M395 linux", I believe. Other than that, I know no more than you do.

[fox]

I've made a bit of progress in getting Ubuntu to boot on my 5k iMac. Using Ubuntu 16.04, I can get it to boot right up when I use the grub parameters acpi=off and nomodeset. These parameters were actually recommended in one posting, but another suggested that nointremap would also boot and have none of the negative effects of acpi=off, so I hadn't tried that before. Unfortunately, while it does boot right up, window response is noticeably slow with these parameters; e.g., moving or expanding windows. Not something that I would be happy with. But at least I know now that a/the major reason for problems booting Ubuntu installers on the 5k iMac relates to acpi. I did try a few other alternative acpi options, but none except turning it off worked. But I don't really get why an acpi setting should relate to a 5k display, unless the problem is more the video card than the display. I wonder if I installed Ubuntu with the acpi=off setting and then added the proprietary Radeon driver if this would solve things. But what is Mint doing that's different because it works fine without the Radeon driver installed?

Speaking of Mint, dropping the default resolution to 2560x1440 does wonders for some of the windows. That's only half the resolution this iMac is capable of, but it's still darn good and I didn't buy that model specifically because of the 5k resolution. Maybe future distros will have kernels with native 5k capability.

[fox]

More progress. I tried a bunch of acpi settings, and besides acpi=off, two other settings work in combination with nomodeset, though they still result in window effects. The two are:

Code Select Expand

acpi=noapic nomodeset

Code Select Expand

acpi=noapic acpi_backlight=vendor nomodeset

I tried both with a Ubuntu 17.04 installation on an SSD run externally. In both cases, boot-up was fast. In the first case, window movement was slow; you could see the delay effects when dragging or expanding a window. In the second case, window movement wasn't slow, but the animation when moving windows was lost. In other words, when you move or expand a window, you see only an outline until the action ceases; then the change shows instantly. But also in the second case, I lose the ability to change the screen brightness through "settings"; the setting to do so in "brightness and lock" is gone. I suspect that the missing brightness setting can be fixed with software. But I don't know the cure for the lose of real time window dragging effects. This is not a big deal, however, so I now have the possibility of installing Ubuntu on my 5k iMac. But since everything seems to be working in Mint, I'm probably going to stick with it now and continue to see how I can fix the window dragging in Ubuntu. Perhaps by installing the proprietary Radeon video card, as suggested by Jason?

[Jason]

It's certainly worth a try since what you're experiencing is definitely related to the driver. It may be that Mint is using an open source Radeon driver whereas 16.10 doesn't see it? Maybe they dropped support for it? System info in either distribution might tell you what driver you're using. Also thinking that Mint probably is still using X.org while the much newer Ubuntu 17.10 is probably using the newer display server (can't recall the name of it right now). So they very likely have at least a slightly different list of available drivers. But honestly, I haven't had to get into video idriver nards in a long time to fix anything but you might have to get optimal performance in Linux. Wish I could help more but I'm out of my league here

[fox]

Jason, your messages are helpful nevertheless and I will look into the driver issue, though I am happy at the moment with using Mint. Incidentally, the newer display server is Wayland, and it might be relevant on Ubuntu 17.10 since it is the default. But Ubuntu 17.04 was still using Xorg.

[bobf]

I like the direction Jason's headed with this issue. My 11" netbook is AMD CPU- and video-based, and AMD drivers were the only thing that could properly address the video subsystem in the hybrid APU. Worse still, it took a two or three updates before the "this driver does not support the installed hardware"-type message in the lower right corner of the screen finally disappeared.

And the following update broke it again... Go figure. It seems fine now, but I may well have reverted back to a default Nouveau driver or something, since, not being a gamer and wanting every last ounce of processing speed out of the GPU segment of the processor, I'd rather have something stable than something blazingly fast.

And when is it *EVER* OK to have to work this hard for it?

[Scott]

I didn't thoroughly read all the replies here before posting, so apologies if this is a repeat.  One of the issues you may be running into is that the computer has dual video.  Either the stock distro may only be detecting the onboard Intel, or may be using the video out as your primary display through the second graphics card.  It may help your queries if you include the dual video nature in your searches.

[fox]

Thanks, Scott. I don't think this iMac has dual video. The video card is described as "AMD Radeon R9 M390 graphics processor with 2GB of GDDR5 memory" and there is no indication of a dual mode. It isn't hooked up to any external monitors, either. Interestingly enough, I just discovered that what is making Mint work is not only the distro and the boot parameters, but also the kernel. The default kernel is 4.8.0-53. I tried upgrading to 4.10.0.37, which is an option given in Mint's Update Manager. When I did so, it wouldn't boot, at least not with the same boot parameters as the older kernel. The text was giving me various errors in "brcmfmac". Go figure! If anything, I would think a newer kernel is better on a relatively new computer.

[bobf]

Now, you*know* that's a wifi error message, right, Mike?! <^8#

(Figures...)

[Scott]

Thanks, Scott. I don't think this iMac has dual video. The video card is described as "AMD Radeon R9 M390 graphics processor with 2GB of GDDR5 memory" and there is no indication of a dual mode. It isn't hooked up to any external monitors, either. Interestingly enough, I just discovered that what is making Mint work is not only the distro and the boot parameters, but also the kernel. The default kernel is 4.8.0-53. I tried upgrading to 4.10.0.37, which is an option given in Mint's Update Manager. When I did so, it wouldn't boot, at least not with the same boot parameters as the older kernel. The text was giving me various errors in "brcmfmac". Go figure! If anything, I would think a newer kernel is better on a relatively new computer.

All of the Mac products have the onboard Intel video (Intel HD Video, Intel Iris Pro etc), if it lists anything other than that, it was one of the higher end options that included dedicated graphics, in your case the Radeon M9 M390.  My MacBook Pro has Intel Iris Pro + GeForce GT 750M.  Any of the lower end offerings, including iMacs and Macbooks only had the onboard Intel video.

This is regularly an issue for operating systems (esp Linux) and isn't isolated to just Apple products.  You see it a lot more in Laptops with dedicated Graphics that can swap video adapters on demand based on performance, or battery requirements.

[fox]

Thanks, Scott. I have another clue about the problems I've had booting or installing distros on this Mac. According to an Arch Linux thread (here), there's no non-apple driver for the 5120x2880 mode (5k). So Windows and Linux alike see the screen as 3840x2160. This includes Linux Mint, but Mint is the only distro I've found so far that will boot immediately without using the nomodeset as a parameter, AND AT THE SAME TIME, give me the option of switching resolution to the lower 4k standard (2560x1440). In that resolution, which is more than good enough for me, I have the option to magnify everything to 2x, which gives me nice text and windows to work from. I have since found a few other distros that will boot immediately with the nomodeset parameter (Ununtu itself, Debian xfce and Sparky Linux lxqt), but none allow me to lower the resolution to from 3840x2160 to 2560x1440. Without that option or a magnification setting between 1 and 2, the windows and text are either too tiny (magnification = 1) or too large (magnification =2). Therein lies my problem. Of equal importance, I cannot get even a Clonezilla usb disk to boot, which means I can't easily clone my Mint installation. (Yes I know I can do it with command line.) So while everything is working OK in Mint 18.2 with the default kernel, I'm feeling vulnerable on this machine without alternatives.

[Jason]

Seeing if there is a proper driver that you can download that is compatible with the kernel you're using should give you other resolution alternatives. Get a nice theme and icons and you can make Linux Mint look pretty good, though.