Using Spack to Replace Homebrew/Conda¶
Spack is an incredibly powerful package manager, designed for supercomputers
where users have diverse installation needs. But Spack can also be used to
handle simple single-user installations on your laptop. Most macOS users are
already familiar with package managers like Homebrew and Conda, where all
installed packages are symlinked to a single central location like
In this section, we will show you how to emulate the behavior of Homebrew/Conda
using Environments (spack.yaml)!
First, let’s create a new environment. We’ll assume that Spack is already set up correctly, and that you’ve already sourced the setup script for your shell. To create a new environment, simply run:
$ spack env create myenv
Here, myenv can be anything you want to name your environment. Next, we can add a list of packages we would like to install into our environment. Let’s say we want a newer version of Bash than the one that comes with macOS, and we want a few Python libraries. We can run:
$ spack -e myenv add bash@5 python py-numpy py-scipy py-matplotlib
Each package can be listed on a separate line, or combined into a single line like we did above. Notice that we’re explicitly asking for Bash 5 here. You can use any spec you would normally use on the command line with other Spack commands.
Next, we want to manually configure a couple of things:
$ spack -e myenv config edit
# This is a Spack Environment file. # # It describes a set of packages to be installed, along with # configuration settings. spack: # add package specs to the `specs` list specs: [bash@5, python, py-numpy, py-scipy, py-matplotlib] view: true
You can see the packages we added earlier in the
specs: section. If you
ever want to add more packages, you can either use
spack add or manually
edit this file.
We also need to change the
concretizer:unify option. By default, Spack
concretizes each spec separately, allowing multiple versions of the same
package to coexist. Since we want a single consistent environment, we want to
concretize all of the specs together.
Here is what your
spack.yaml looks like with this new setting:
# This is a Spack Environment file. # # It describes a set of packages to be installed, along with # configuration settings. spack: # add package specs to the `specs` list specs: [bash@5, python, py-numpy, py-scipy, py-matplotlib] view: true concretizer: unify: true
To actually concretize the environment, run:
$ spack -e myenv concretize
This will tell you which if any packages are already installed, and alert you to any conflicting specs.
To actually install these packages and symlink them to your
directory, simply run:
$ spack -e myenv install $ spack env activate myenv
Now, when you type
which python3, it should find the one you just installed.
In order to change the default shell to our newer Bash installation, we first need to add it to this list of acceptable shells. Run:
$ sudo vim /etc/shells
and add the absolute path to your bash executable. Then run:
$ chsh -s /path/to/bash
Now, when you log out and log back in,
echo $SHELL should point to the
newer version of Bash.
Updating Installed Packages¶
Let’s say you upgraded to a new version of macOS, or a new version of Python was released, and you want to rebuild your entire software stack. To do this, simply run the following commands:
$ spack env activate myenv $ spack concretize --fresh --force $ spack install
--fresh flag tells Spack to use the latest version of every package
where possible instead of trying to optimize for reuse of existing installed
--force flag in addition tells Spack to overwrite its previous
concretization decisions, allowing you to choose a new version of Python.
If any of the new packages like Bash are already installed,
won’t re-install them, it will keep the symlinks in place.
Updating & Cleaning Up Old Packages¶
If you’re looking to mimic the behavior of Homebrew, you may also want to clean up out-of-date packages from your environment after an upgrade. To upgrade your entire software stack within an environment and clean up old package versions, simply run the following commands:
$ spack env activate myenv $ spack mark -i --all $ spack concretize --fresh --force $ spack install $ spack gc
spack mark -i --all tells Spack to mark all of the existing
packages within an environment as “implicitly” installed. This tells
spack’s garbage collection system that these packages should be cleaned up.
Don’t worry however, this will not remove your entire environment.
spack install will reexamine your spack environment after
a fresh concretization and will re-mark any packages that should remain
installed as “explicitly” installed.
Note: if you use multiple spack environments you should re-run
in each of your environments prior to running
spack gc to prevent spack
from uninstalling any shared packages that are no longer required by the
environment you just upgraded.
If you decide that Spack isn’t right for you, uninstallation is simple. Just run:
$ spack env activate myenv $ spack uninstall --all
This will uninstall all packages in your environment and remove the symlinks.