Your CMake version should be newer than your compiler. It should be newer than the libraries you are using (especially Boost). New versions work better for everyone.
If you have a built in copy of CMake, it isn't special or customized for your system. You can easily install a new one instead, either on the system level or the user level. Feel free to instruct your users here if they complain about a CMake requirement being set too high. Especially if they want 3.1+ support. Maybe even if they want 3.21+ support...
You can [download CMake from KitWare][download]. This is how you will probably get CMake if you are on Windows. It's not a bad way to get it on macOS either (and a Universal2 version is supplied supporting both Intel and Apple Silicon), but using `brew install cmake` is much nicer if you use [Homebrew](https://brew.sh) (and you should; Apple even supports Homebrew such as during the Apple Silicon rollout). You can also get it on most other package managers, such as [Chocolatey](https://chocolatey.org) for Windows or [MacPorts](https://www.macports.org) for macOS.
On Linux, there are several options. Kitware provides a [Debian/Ubunutu apt repository][apt], as well as [snap packages][snap]. There are universal Linux binaries provided, but you'll need to pick an install location. If you already use `~/.local` for user-space packages, the following single line command[^1] will get CMake for you [^2]:
And, if you want a system install, install to `/usr/local`; this is an excellent choice in a Docker container, for example on GitLab CI. Do not try it on a non-containerized system.
Here are some common build environments and the CMake version you'll find on them. Feel free to install CMake yourself, it's 1-2 lines and there's nothing "special" about the built in version. It's also very backward compatible.
[](https://pkgs.alpinelinux.org/packages?name=cmake&branch=v3.12)
Just `pip install cmake` on many systems. Add `--user` if you have to (modern pip does this for you if needed). This does not supply Universal2 wheels yet.
| [TravisCI Xenial](https://docs.travis-ci.com/user/reference/xenial/#compilers-and-build-toolchain) | 3.12.4 | Mid November 2018 this image became ready for widescale use. |
| [TravisCI Bionic](https://docs.travis-ci.com/user/reference/bionic/#compilers-and-build-toolchain) | 3.12.4 | Same as Xenial at the moment. |
If you are using GitHub Actions, also see the [jwlawson/actions-setup-cmake](https://github.com/marketplace/actions/actions-setup-cmake) action, which can install your selection of CMake, even in a docker action run.
[This][PyPI] is also provided as an official package, maintained by the authors of CMake at KitWare. It's a rather new method, and might fail on some systems (Alpine isn't supported last I checked, but that has a recent CMake), but works really well when it works (like on Travis CI). If you have pip (Python's package installer), you can do:
And as long as a binary exists for your system, you'll be up-and-running almost immediately. If a binary doesn't exist, it will try to use KitWare's `scikit-build` package to build, which currently can't be listed as a dependency in the packaging system, and might even require (an older) copy of CMake to build. So only use this system if binaries exist, which is most of the time.
This has the benefit of respecting your current virtual environment, as well. It really shines when placed in a `pyproject.toml` file, however - it will only be installed to build your package, and will not remain afterwords! Fantastic.
Personally, on Linux, I put versions of CMake in folders, like `/opt/cmake312` or `~/opt/cmake312`, and then add them to [LMod][]. See [`envmodule_setup`][envmodule_setup] for help setting up an LMod system on macOS or Linux. It takes a bit to learn, but is a great way to manage package and compiler versions.
[^1]: I assume this is obvious, but you are downloading and running code, which exposes you to a man in the middle attack. If you are in a critical environment, you should download the file and check the checksum. (And, no, simply doing this in two steps does not make you any safer, only a checksum is safer).
[^2]: If you don't have a `.local` in your home directory, it's easy to start. Just make the folder, then add `export PATH="$HOME/.local/bin:$PATH"` to your `.bashrc` or `.bash_profile` or `.profile` file in your home directory. Now you can install any packages you build to `-DCMAKE_INSTALL_PREFIX=~/.local` instead of `/usr/local`!
