By Anil Madhavapeddy - 2024-04-24
MirageOS consists of a set of OCaml libraries that link with a runtime to form either a standalone unikernel or a normal UNIX binary. These libraries are managed via the OPAM tool. After describing MirageOS's system requirements, we will introduce the basics of OPAM and setting up for MirageOS.
MirageOS has been tested on many modern Linux distributions, macOS 10.10+ and FreeBSD 11+.
You will need OPAM 2.1.0 or later and OCaml 4.12.1 or later.
Further requirements for the host/build system depend on the specific backend in use:
xen
or qubes
backend, you must have a 64-bit Linux or FreeBSD host. To run Xen unikernels, you must have a 64-bit host capable of Xen PVHv2, i.e. Xen version 4.10 or later, or Qubes OS 4.0.hvt
backend is supported on Linux (x86_64
, aarch64
), FreeBSD and OpenBSD (x86_64
) hosts. Running hvt
unikernels requires a host system with access to hardware virtualization.spt
backend, or run an spt
unikernel, you must have a Linux (x86_64
or aarch64
) host.x86_64
architecture, such as Google Compute Engine. Building is supported on Linux, FreeBSD and OpenBSD.If you are using Homebrew, run
brew install opam
opam init
opam install mirage
This has the latest packages required in the base distribution, so just run:
sudo apt-get update
sudo apt-get install opam
opam init
opam install mirage
The version of OPAM in older Ubuntus is not high enough to run Mirage (which requires OPAM 2.1.0 or higher), so you will need to add a custom PPA for the latest packages:
sudo add-apt-repository ppa:avsm/ppa
sudo apt-get update
sudo apt-get install ocaml ocaml-native-compilers camlp4-extra opam
opam init
opam install mirage
This has the latest packages required in the base distribution, so just run:
sudo apt-get update
sudo apt-get install opam
opam init
opam install mirage
You will need ports or pkg
set up. To install OPAM use the ocaml-opam
port/package.
For notes specific to installing and running MirageOS on ARM64 (including embedded boards such as the Raspberry Pi 3), see this page.
We use OPAM to manage OCaml compiler and library installations. It tracks library versions across upgrades and will recompile dependencies automatically if they get out of date. Please refer to OPAM documentation if you want to know more, but we will cover the basics to get you started here. There is a Quick Install Guide if the above instructions don't cover your operating system.
Note that you require OPAM 2.1.0 or greater to use with MirageOS. Some distribution packages provide earlier versions and must be updated; check with
$ opam --version ## response should be at least 2.1.0 viz.
2.1.2
All the OPAM state is held in the .opam
directory in your home directory, including compiler installations. You should never need to switch to a root user to install packages. Package listings are obtained through remote
sources, which defaults to the contents of github.com/ocaml/opam-repository.
After installation, opam update -u
refreshes the package list and recompiles packages to the latest versions. You should run this regularly to get the latest packages.
$ opam init
# list of your remotes, which should include opam.ocaml.org
$ opam remote
Next, make sure you have at least OCaml 4.12.1 or higher as your active compiler. This is generally the case on macOS, though Debian only has it in the testing distribution at present. But don't worry: if your compiler is out of date, just run opam switch
to have it locally install the right version for you.
$ ocaml -version
# if it is not 4.12.1 or higher, then run this
$ opam switch 4.13.1
Once you've got the right version, set up your shell environment to point to the current compiler switch.
$ eval `opam config env`
# add the above line to your startup shell profile
This updates the variables in your shell to match the current OPAM installation, mainly by altering your system PATH
. You can see the shell fragment by running opam config env
at any time. If you add the eval
line to your login shell (usually ~/.bash_profile
), it will automatically import the correct PATH on every subsequent login.
Check that the base packages are installed correctly:
$ opam list
Installed packages for system:
base-bigarray base Bigarray library distributed with the OCaml compiler
base-threads base Threads library distributed with the OCaml compiler
base-unix base Unix library distributed with the OCaml compiler
[ possibly other installed packages ]
Finally, install the MirageOS command-line tool.
$ opam install mirage
$ mirage --help
That's it. You now have everything required to start developing MirageOS unikernels that will run either as POSIX processes or as standalone unikernels. Next, why not try building a MirageOS hello world?