Build Caches

Some sites may encourage users to set up their own test environments before carrying out central installations, or some users may prefer to set up these environments on their own motivation. To reduce the load of recompiling otherwise identical package specs in different installations, installed packages can be put into build cache tarballs, uploaded to your Spack mirror and then downloaded and installed by others.

Creating build cache files

A compressed tarball of an installed package is created. Tarballs are created for all of its link and run dependency packages as well. Compressed tarballs are signed with gpg and signature and tarball and put in a .spack file. Optionally, the rpaths (and ids and deps on macOS) can be changed to paths relative to the Spack install tree before the tarball is created.

Build caches are created via:

$ spack buildcache create <spec>

If you wanted to create a build cache in a local directory, you would provide the -d argument to target that directory, again also specifying the spec. Here is an example creating a local directory, “spack-cache” and creating build cache files for the “ninja” spec:

$ mkdir -p ./spack-cache
$ spack buildcache create -d ./spack-cache ninja
==> Buildcache files will be output to file:///home/spackuser/spack/spack-cache/build_cache
gpgconf: socketdir is '/run/user/1000/gnupg'
gpg: using "E6DF6A8BD43208E4D6F392F23777740B7DBD643D" as default secret key for signing

Note that the targeted spec must already be installed. Once you have a build cache, you can add it as a mirror, discussed next.

Finding or installing build cache files

To find build caches or install build caches, a Spack mirror must be configured with:

$ spack mirror add <name> <url>

Note that the url can be a web url _or_ a local filesystem location. In the previous example, you might add the directory “spack-cache” and call it mymirror:

$ spack mirror add mymirror ./spack-cache

You can see that the mirror is added with spack mirror list as follows:

$ spack mirror list
mymirror           file:///home/spackuser/spack/spack-cache
spack-public       https://spack-llnl-mirror.s3-us-west-2.amazonaws.com/

At this point, you’ve create a buildcache, but spack hasn’t indexed it, so if you run spack buildcache list you won’t see any results. You need to index this new build cache as follows:

$ spack buildcache update-index -d spack-cache/

Now you can use list:

$  spack buildcache list
==> 1 cached build.
-- linux-ubuntu20.04-skylake / gcc@9.3.0 ------------------------
ninja@1.10.2

Great! So now let’s say you have a different spack installation, or perhaps just a different environment for the same one, and you want to install a package from that build cache. Let’s first uninstall the actual library “ninja” to see if we can re-install it from the cache.

$ spack uninstall ninja

And now reinstall from the buildcache

$ spack buildcache install ninja
==> buildcache spec(s) matching ninja
==> Fetching file:///home/spackuser/spack/spack-cache/build_cache/linux-ubuntu20.04-skylake/gcc-9.3.0/ninja-1.10.2/linux-ubuntu20.04-skylake-gcc-9.3.0-ninja-1.10.2-i4e5luour7jxdpc3bkiykd4imke3mkym.spack
####################################################################################################################################### 100.0%
==> Installing buildcache for spec ninja@1.10.2%gcc@9.3.0 arch=linux-ubuntu20.04-skylake
gpgconf: socketdir is '/run/user/1000/gnupg'
gpg: Signature made Tue 23 Mar 2021 10:16:29 PM MDT
gpg:                using RSA key E6DF6A8BD43208E4D6F392F23777740B7DBD643D
gpg: Good signature from "spackuser (GPG created for Spack) <spackuser@noreply.users.github.com>" [ultimate]

It worked! You’ve just completed a full example of creating a build cache with a spec of interest, adding it as a mirror, updating it’s index, listing the contents, and finally, installing from it.

Note that the above command is intended to install a particular package to a build cache you have created, and not to install a package from a build cache. For the latter, once a mirror is added, by default when you do spack install the --use-cache flag is set, and you will install a package from a build cache if it is available. If you want to always use the cache, you can do:

$ spack install --cache-only <package>

For example, to combine all of the commands above to add the E4S build cache and then install from it exclusively, you would do:

$ spack mirror add E4S https://cache.e4s.io
$ spack buildcache keys --install --trust
$ spack install --cache-only <package>

We use --install and --trust to say that we are installing keys to our keyring, and trusting all downloaded keys.

Relocation

Initial build and later installation do not necessarily happen at the same location. Spack provides a relocation capability and corrects for RPATHs and non-relocatable scripts. However, many packages compile paths into binary artifacts directly. In such cases, the build instructions of this package would need to be adjusted for better re-locatability.

spack buildcache

spack buildcache create

Create tarball of installed Spack package and all dependencies. Tarballs are checksummed and signed if gpg2 is available. Places them in a directory build_cache that can be copied to a mirror. Commands like spack buildcache install will search Spack mirrors for build_cache to get the list of build caches.

Arguments Description
<specs> list of partial specs or hashes with a leading / to match from installed packages and used for creating build caches
-d <path> directory in which build_cache directory is created, defaults to .
-f overwrite .spack file in build_cache directory if it exists
-k <key> the key to sign package with. In the case where multiple keys exist, the package will be unsigned unless -k is used.
-r make paths in binaries relative before creating tarball
-y answer yes to all create unsigned build_cache questions

spack buildcache list

Retrieves all specs for build caches available on a Spack mirror.

Arguments Description
<specs> list of partial package specs to be matched against specs downloaded for build caches

E.g. spack buildcache list gcc with print only commands to install gcc package(s)

spack buildcache install

Retrieves all specs for build caches available on a Spack mirror and installs build caches with specs matching the specs input.

Arguments Description
<specs> list of partial package specs or hashes with a leading / to be installed from build caches
-f remove install directory if it exists before unpacking tarball
-y answer yes to all to don’t verify package with gpg questions

spack buildcache keys

List public keys available on Spack mirror.

Arguments Description
-i trust the keys downloaded with prompt for each
-y answer yes to all trust all keys downloaded