Install macOS Big Sur 11.0.1 RC2 in a VM (QEMU)

Install macOS Big Sur 11.0.1 RC2 in a VM (QEMU)

A new macOS release is nearing release, and it's a big one. So big that this time it's really, completely and definitely not OS X any longer. With the death of Kexts looming and the transition away from Intel CPUs spelling disaster for Hackintoshers and multi-OS users alike, it's certainly an interesting time.

Oh, and rounded edges. So many rounded edges. Good golly.

Update 2020-11-11: This guide has been updated to support Big Sur 11.0.1 Release Candidate 2 (Beta 3).
Update 2020-11-13: For the specific steps required to get the Big Sur public release to work, I made a companion post:
Install macOS Big Sur 10.0.1 public release in a VM (QEMU)
This is a small addendum to my main article on how to install macOS in a VM, which I’ll keep as-is as that’s effectively the normal way. But, if you’d like to jump on the fresh-off-the-press public release of Big Sur, here’s what you have to do to make that

Today I'd like to walk you through how to get Big Sur installed and up and running in a virtual machine on your Ubuntu or similar host machine. In this article I'll focus on steps and commands that are tailored towards Ubuntu 20.04, but I'm sure you'll be able to tweak things a bit to tailor towards whatever flavor you're running to get things to work similarly.

Let's get to it.

As of this writing, Big Sur 11.0.1 Release Candidate 2 (Beta 3) was the recent-most beta release. The fetch-macOS script might need updating for future beta releases and the eventual full release. Please check the relevant repositories for up-to-date information on this.


In this guide I'll assume you have already set up your host machine, including having set up QEMU, virt-manager, etc. As mentioned before, I'm focussing this guide on running Ubuntu 20.04 as the host OS.

No physical Mac needed

You do not need a physical Mac to download anything necessary to create this VM. We'll be using a few tools to fetch and extract the installer files needed right from your host machine.


Be sure to have Python installed. In my case I already had Python installed but I needed to install an extra package called python-is-python2 to get certain tools to work, but you might also want to make sure python2 is actually installed.

Build tools

We'll be building a few tools from source, so we'll need build tools installed for that. To be honest I already had most of these installed, so I am probably going to miss one or two in this list. If one of the build steps later on this guide fails, it'll tell you what's missing so you can install it at that point. Please let me know if I did actually miss anything here.

sudo apt install build-essential cmake clang libfuse-dev libbz2-dev libudev-dev libxml2-dev linux-headers-generic pkg-config zlib1g-dev libicu-dev openssl

Other utilities

Also be sure to install these tools if you don't have them already:

sudo apt install dmg2img p7zip
What's happening: We'll need dmg2img to convert an image file, and while 7zip is optional, it's a great compression and decompression tool that I highly recommend you keep around as it's super convenient.

Check out the OSX-KVM repo

Both literally and figuratively. Most of the work has been done by the amazing people who have created and keep this repository up-to-date. There's a few minor tweaks we'll make to get Beta 3 to work, which at the time of this writing isn't yet working out of the box when relying on the original repo (I have submitted a PR for this). Hopefully this'll get added soon, but for now you can head over to my fork where I've already applied the fix needed to get Beta 3 to download. The main repo has since been updated and should automatically fetch the recent-most beta.

Go ahead and download the repo to your local machine.

Download the Big Sur installer file

Open up a Terminal and from the OSX-KVM repo you have just downloaded, and run:

./ --big-sur

You should see a bunch of things fly by and the tool will start downloading a relatively humongous InstallAssistant.pkg file, clocking in at 12GB.

Note: If you have issues at this step, it is possible an incomplete plist file has been downloaded, or perhaps a complete but now out-of-date version. The tool keeps using an already downloaded file if it exists, so if you get a warning about something related to XML parsing or you're not getting the version you expect, try deleting the files found in content/catalogs/other and running the tool again.

While this is downloading, let's set up a few additional things we'll need once the download is done.

Download & build XAR

Download the XAR repository here, and open another Terminal window/tab and head over to where you have downloaded this repository. The project does not seem to be actively maintained, and as of 2022-08-29 this PR has not yet been merged. If it has by the time you read this, you can proceed right away. If not, we need to apply this fix ourselves to be able to continue. Fortunately the fix is quick:

Open up xar/ using your favorite text editor, and find line :332. Change the part that says OpenSSL_add_all_ciphers so that it instead says CRYPTO_free. The result should look something like this:

 AC_CHECK_HEADERS([openssl/evp.h], , [have_libcrypto="0"])
-AC_CHECK_LIB([crypto], [OpenSSL_add_all_ciphers], , [have_libcrypto="0"])
+AC_CHECK_LIB([crypto], [CRYPTO_free], , [have_libcrypto="0"])
 if test "x${have_libcrypto}" = "x0" ; then
   AC_MSG_ERROR([Cannot build without libcrypto (OpenSSL)])

With that done, you can now run the following to build xar:

cd xar && ./ && make
What's happening: We head into the xar sub-directory, run to generate the configure script, and then build the project with make. We're not installing the tool, so the results stay contained within this folder.

Download & build darling-dmg

Download the darling-dmg repository from here, and head on over to this directory in a Terminal window. Darling-dmg is a part of Darling, a sort of WINE for macOS software, which I didn't even know was a thing that existed until I was going through this process. Regardless, we don't need the entire Darling project, so that's why we're just pulling in darling-dmg.

If you already have Darling installed on your system, you can skip this step as you should already have darling-dmg available.

From the darling-dmg repository folder, run the following:

cmake . && make
What's happening: We're just configuring and building darling-dmg here. We're not installing it, so the results stay contained within this folder. If the build fails, please check the results as this is probably due to a missing library. Simply look through the messages to find the library you're missing, apt install it, and try again.

Extract & prepare the installer image

By this point the download has hopefully finished, and you should have InstallAssistant.pkg sitting right there in your OSX-KVM folder. We'll have to take a few steps now to get to the actual installer image file, so let's do that now.

Make note where the XAR and darling-dmg folders are relative to your OSX-KVM folder, as we'll have to use these now.

Step 1: Extract InstallAssistant.pkg

Let's create a folder in which we'll extract all files to, to keep the repo from getting messy:

mkdir extracted

In a Terminal window opened to your OSX-KVM folder, let's now extract the PKG file:

../path/to/xar-repo-dir/xar/src/xar -xf InstallAssistant.pkg -C ./extracted
What's happening: We're using the xar tool we build just before to extract the file by pointing to it relative to your OSX-KVM folder. The built tool should be at xar/src/xar within the folder where you have checked out the XAR repository. -x tells the tool you want to extract, and with -f filename you specify which file you want to extract from. Lastly, -C ./extracted tells it to extract the files to the specified folder we have created just previously.

After a bit, a few new files should have shown up inside the extracted folder, including SharedSupport.dmg.

Step 2: Mount SharedSupport.dmg

Now we'll use darwin-dmg to mount SharedSupport.dmg. In Terminal, run:

mkdir tmp && ../path/to/darling-dmg-repo-dir/darling-dmg extracted/SharedSupport.dmg tmp
What's happening: We're creating a folder called tmp, which we'll use to mount the disk image to. We then use darling-dmg by referencing it from the folder we checked out its repository to, and specify we want to mount SharedSupport.dmg to the just-created tmp folder.

If this went well, you should see a few messages in your Terminal, and a newly mounted drive show up in your file manager called tmp. If you want to stick to using Terminal, you should also see these files when cd'ing into it; cd tmp && ls -la.

Step 3: Extract BaseSystem.dmg

With SharedSupport.dmg mounted, we need to extract BaseSystem.dmg, which is located inside a ZIP file. Using 7zip, run this from your OSX-KVM directory:

7z e ./tmp/com_apple_MobileAsset_MacSoftwareUpdate/*.zip AssetData/Restore/BaseSystem.dmg -o./extracted
What's happening: We're extracting BaseSystem.dmg from a ZIP file found inside the SharedSupport.dmg image we have just before mounted to ./tmp. The ZIP file is located inside the com_apple_MobileAsset_MacSoftwareUpdate sub-directory, and BaseSystem.dmg is located in AssetData/Restore within that ZIP file. If you like, you can use your favorite file manager and archive tool to extract this directly too. The -o./extracted flag lets 7zip extract to the "extracted" folder we have just before created, to keep our repository directory nice and clean.

Step 4: Convert BaseSystem.dmg

We'll now use the dmg2img tool to, as the name implies, convert the image to the img format, something that QEMU can actually work with. Simply run:

dmg2img extracted/BaseSystem.dmg extracted/BaseSystem.img

A moment or two later you should have the macOS Big Sur installation disk image ready to go. Exciting!

We're now done with both DMG files, so let's unmount SharedSupport.dmg and remove the tmp dir. You can now also delete both files if you like:

umount tmp && rmdir tmp;

# If you would like to delete the DMG files now too:
rm extracted/{SharedSupport.dmg,BaseSystem.dmg,Bom,PackageInfo,Payload,Scripts}

Starting up the VM

The OSX-KVM repository comes with a convenient shell script that you can use to easily launch the VM directly. This file has everything you need pre-configured, though the defaults are probably not ideal if you're planning to use this VM for anything more than just gazing upon it once or so. For example, only 3GB RAM is allocated to it, which is a tiny amount of course.

If you're just curious, or if you want to use this script to sort of jump-start the installation of macOS after which you'll move the disk image with Big Sur installed on it over to a more permanent VM configuration, this might be a handy starting point. Otherwise, you might want to skip ahead to the section on using virt-manager.

Method 1: For quick testing, momentary curiosity, or for use as a starting point

The script is called and assumes you're launching it from within the repo's directory, have BaseSystem.img ready to go, have a hard drive disk image created, and have the "default" network adapter all set up and ready to go. We're two for four here, so let's go ahead and tackle those last two bits. First, let's create a disk image we'll install Big Sur onto:

qemu-img create -f qcow2 mac_hdd_ng.img 128G
What's happening: We're using the qemu-img tool to create a new disk image called mac_hdd_ng.img that's 128GB in size. Be sure to customize the size to your liking, in case you need more (or less) space.
Note: If you get a message saying you don't have qemu-img installed, you probably didn't install qemu-utils.

Next, let's set up some basic networking so this VM can actually boot up:

sudo ip tuntap add dev tap0 mode tap
sudo ip link set tap0 up promisc on
sudo ip link set dev virbr0 up
sudo ip link set dev tap0 master virbr0

virsh net-start default
virsh net-autostart default
What's happening: We're basically setting up and configuring a bridge network connection which VMs can use to connect to the internet. For anything beyond quick testing you'll probably want to set up a more robust configuration or pass through an actual network adapter if you have multiple, but for now this should at least get you going.

Lastly, as we kept all prepared files in a subdirectory, we should modify the script to point to the right directory. While we're in there, we might as-well update the RAM allocation, unless 3GB is enough for your specific needs of course.

You can find the reference to $REPO_PATH/BaseSystem.img on line :52. Simply update it to read $REPO_PATH/extracted/BaseSystem.img and that should be it. If you have created the qemu hard drive image someplace else or used a different name, you can update that reference on line :53. Lastly, the amount of RAM the VM will use is specified on line :21 in the ALLOCATED_RAM variable. 8192 (8GiB) might be a good choice, or 16384 (16GiB) if you can spare it and are planning to do Mac/iOS development for example.

Now you should be able to boot up the VM for the first time! To start it, just run from a Terminal window, and a QEMU remote viewer screen should show up soon thereafter.

After a brief moment, a familiar screen will show up with a few options. Simply hit enter to boot the first option (called macOS Base System), which is the installation disk image.

Note: The OpenCore configuration included with this repository has verbose mode enabled, so you'll be seeing a lot of messages run by as the system (and the installer) boot up. This is normal and intended. You'll be able to modify the OpenCore configuration file to disable this should you want to, but that's outside the scope of this already rather lengthy article :).

From here you can proceed as you normally would. Before you start with the installation, be sure to launch into Disk Utility the first time so you can format the disk image.

After selecting and launching Disk Utility from the main menu, select Show All Devices from the sidebar options menu. Then, with the correct disk image selected (you can double check the capacity to make sure you're looking at the right drive), click Erase, name your drive and select your preferred options (Encrypted or not, Case-sensitive or not), and click Erase.

Note that in my case I was not able to actually start the Big Sur Beta installation on a drive that I formatted using the APFS Encrypted option. I am not sure if it was a limitation of the specific beta I was installing or something else. If you run into the same issue, try re-formatting the drive to non-Encrypted APFS. Your root drive should already be encrypted so it's probably not the end of the world, and I'm sure the non-beta version will certainly support encrypted drives again.

When you're done with that, click Done, close Disk Utility, and select Reinstall macOS from the main menu. From there you can follow the steps as you normally would.

Note: As you probably know, at one point during installation the VM will reboot. To let it continue with the installation, at the boot selection screen be sure to select the macOS Install option, as that's the as-of-yet incomplete installation of macOS on the hard drive.

After about an hour or so of you should be greeted with the welcome stuff, where you can set up your user account and whatnot. And after that, well, get ready for border radii to dazzle you with their roundedness.

Well hello there, Big Sur.

Closing thoughts

At this point you should have a working macOS Big Sur VM. Congrats! But it might not be the most elegant of setups. You'll have to use to launch the VM every time, and you'll probably notice that macOS itself feels rather sluggish too. The latter is due to the lack of any form of hardware acceleration, something you can only really fix by passing through a graphics card.

I hope this was useful for you and that this guide has helped you get to a working virtual machine. Enjoy, and happy coding!

Thank you.