xhyve – Lightweight Virtualization on OS X Based on bhyve

The Hypervisor.framework user mode virtualization API introduced in Mac OS X 10.10 (Yosemite) cannot only be used for toy projects like the hvdos DOS Emulator, but is full-featured enough to support a full virtualization solution that can for example run Linux.

xhyve is a lightweight virtualization solution for OS X that is capable of running Linux. It is a port of FreeBSD’s bhyve, a KVM+QEMU alternative written by Peter Grehan and Neel Natu.

• super lightweight, only 230 KB in size
• completely standalone, no dependencies
• the only BSD-licensed virtualizer on OS X
• does not require a kernel extension (bhyve’s kernel code was ported to user mode code calling into Hypervisor.framework)
• multi-CPU support
• networking support
• can run off-the-shelf Linux distributions (and could be extended to run other operating systems)

xhyve may make a good solution for running Docker on your Mac, for instance.

Running Tiny Core Linux on xhyve

The xhyve repository already contains a small Linux system for testing, so you can try out xhyve by just typing these few lines:

$ git clone https://github.com/mist64/xhyve
$ cd xhyve
$ make
$ ./xhyverun.sh

And you will see Tiny Core Linux booting in your terminal window:

Initializing cgroup subsys cpuset
Initializing cgroup subsys cpu
Initializing cgroup subsys cpuacct
Linux version 3.16.6-tinycore64 (tc@box) (gcc version 4.9.1 (GCC) ) #777 SMP Thu Oct 16 10:21:00 UTC 2014
Command line: earlyprintk=serial console=ttyS0 acpi=off
e820: BIOS-provided physical RAM map:
BIOS-e820: [mem 0x0000000000000000-0x000000000009fbff] usable
BIOS-e820: [mem 0x0000000000100000-0x000000003fffffff] usable
NX (Execute Disable) protection: active
SMBIOS 2.6 present.
AGP: No AGP bridge found
e820: last_pfn = 0x40000 max_arch_pfn = 0x400000000
x86 PAT enabled: cpu 0, old 0x7040600070406, new 0x7010600070106
CPU MTRRs all blank - virtualized system.

[...]

 (?-
 //\   Core is distributed with ABSOLUTELY NO WARRANTY.
 v_/_           www.tinycorelinux.com

tc@box:~$

To shut down the VM and exit to the Mac’s command line, enter:

$ sudo halt

Running Ubuntu on xhyve

You can also install a more complete Linux distribution on xhyve. The tricky bit is that xhyve doesn’t come with a BIOS or EFI booter, so it is necessary to extract the kernel and initrd from the Linux image and pass them to xhyve manually.

First download Ubuntu Server (the desktop version doesn’t support the text mode installer) into the directory “ubuntu” inside the “xhyve” directory:

$ ls -l
total 1218560
-rw-r--r--@ 1 mist  staff  623902720  6 Jun 22:14 ubuntu-14.04.2-server-amd64.iso

We need to extract the kernel and initrd, which is a little tricky, because OS X doesn’t recognize the hybrid file system on the image without a little hack:

$ dd if=/dev/zero bs=2k count=1 of=/tmp/tmp.iso
$ dd if=ubuntu-14.04.2-server-amd64.iso bs=2k skip=1 >> /tmp/tmp.iso
$ hdiutil attach /tmp/tmp.iso
$ cp /Volumes/Ubuntu-Server\ 14/install/vmlinuz .
$ cp /Volumes/Ubuntu-Server\ 14/install/initrd.gz .

Create a virtual hard disk image (8 GB in the example):

$ dd if=/dev/zero of=hdd.img bs=1g count=8

Then create a script to run xhyve with the correct arguments for the installer:

#!/bin/sh

KERNEL="ubuntu/vmlinuz"
INITRD="ubuntu/initrd.gz"
CMDLINE="earlyprintk=serial console=ttyS0 acpi=off"

MEM="-m 1G"
#SMP="-c 2"
NET="-s 2:0,virtio-net"
IMG_CD="-s 3,ahci-cd,ubuntu/ubuntu-14.04.2-server-amd64.iso"
IMG_HDD="-s 4,virtio-blk,ubuntu/hdd.img"
PCI_DEV="-s 0:0,hostbridge -s 31,lpc"
LPC_DEV="-l com1,stdio"

build/xhyve $MEM $SMP $PCI_DEV $LPC_DEV $NET $IMG_CD $IMG_HDD -f kexec,$KERNEL,$INITRD,"$CMDLINE"

You will want networking enabled, so it’s easiest to run the script as root (this requirement is lifted if you codesign the binary):

$ sudo ./xhyverun_ubuntu_install.sh

You will see the Ubuntu text mode installer:

  ┌───────────────────────┤ [!!] Select a language ├────────────────────────┐
  │                                                                         │
  │ Choose the language to be used for the installation process. The        │
  │ selected language will also be the default language for the installed   │
  │ system.                                                                 │
  │                                                                         │
  │ Language:                                                               │
  │                                                                         │
  │                               C                                         │
  │                               English                                   │
  │                                                                         │
  │     <Go Back>                                                           │
  │                                                                         │
  └─────────────────────────────────────────────────────────────────────────┘

<Tab> moves; <Space> selects; <Enter> activates buttons

All answers should be straightforward, and the defaults are usually fine. Make sure to select “Yes” when asked “Install the GRUB boot loader to the master boot record”.

At the very end, on the “Installation complete” screen, select “Go back” and “Execute a shell”, so you can copy the installed kernel and initrd to the Mac side. In the VM, type this:

# cd /target
# sbin/ifconfig
# tar c boot | nc -l -p 1234

On the Mac, type this, replacing the IP with the output from ifconfig before:

$ cd ubuntu
$ nc 192.168.64.7 1234 | tar x

In the VM, exit the shell:

# exit

Then select “Finish the installation”.

To run the Ubuntu installation from the virtual hard disk, create the following script, fixing up the kernel and initrd version numbers:

#!/bin/sh

KERNEL="ubuntu/boot/vmlinuz-3.16.0-30-generic"
INITRD="ubuntu/boot/initrd.img-3.16.0-30-generic"
CMDLINE="earlyprintk=serial console=ttyS0 acpi=off root=/dev/vda1 ro"

MEM="-m 1G"
#SMP="-c 2"
NET="-s 2:0,virtio-net"
IMG_HDD="-s 4,virtio-blk,ubuntu/hdd.img"
PCI_DEV="-s 0:0,hostbridge -s 31,lpc"
LPC_DEV="-l com1,stdio"

build/xhyve $MEM $SMP $PCI_DEV $LPC_DEV $NET $IMG_CD $IMG_HDD -f kexec,$KERNEL,$INITRD,"$CMDLINE"

Then run the script:

$ sudo ./xhyverun_ubuntu.sh

To make your Linux installation useful, you may want to install an SSH server:

$ sudo apt-get install openssh-server

Or install a full UI that you can access using VNC:

$ sudo apt-get install xubuntu-desktop vnc4server

Then run the VNC server:

$ vnc4server :0 -geometry 1024x768

And conntect to it by pasting this into Finder’s Cmd+K “Connect to Server” dialog:

vnc://ubuntu.local

If you also follow skerit’s Ubuntu VNC tutorial, you’ll get to a desktop like this.

Next Steps

xhyve is very basic and lightweight, but it has a lot of potential. If you are a developer, you are welcome to contribute to it. A list of current TODOs and ideas is part of the README file in the repository.