Bootstrapping

In the Getting started Section we already mentioned that Spack can bootstrap some of its dependencies, including clingo. In fact, there is an entire command dedicated to the management of every aspect of bootstrapping:

$ spack bootstrap --help
usage: spack bootstrap [-h] SUBCOMMAND ...

manage bootstrap configuration

positional arguments:
  SUBCOMMAND
    status    get the status of Spack
    enable    enable bootstrapping
    disable   disable bootstrapping
    reset     reset bootstrapping configuration to Spack defaults
    root      get/set the root bootstrap directory
    list      list all the sources of software to bootstrap Spack
    trust     trust a bootstrapping source
    untrust   untrust a bootstrapping source
    add       add a new source for bootstrapping
    remove    remove a bootstrapping source
    mirror    create a local mirror to bootstrap Spack

optional arguments:
  -h, --help  show this help message and exit

The first thing to know to understand bootstrapping in Spack is that each of Spack’s dependencies is bootstrapped lazily; i.e. the first time it is needed and can’t be found. You can readily check if any prerequisite for using Spack is missing by running:

% spack bootstrap status
Spack v0.17.1 - python@3.8

[FAIL] Core Functionalities
  [B] MISSING "clingo": required to concretize specs

[FAIL] Binary packages
  [B] MISSING "gpg2": required to sign/verify buildcaches


Spack will take care of bootstrapping any missing dependency marked as [B]. Dependencies marked as [-] are instead required to be found on the system.

In the case of the output shown above Spack detected that both clingo and gnupg are missing and it’s giving detailed information on why they are needed and whether they can be bootstrapped. Running a command that concretize a spec, like:

% spack solve zlib
==> Bootstrapping clingo from pre-built binaries
==> Fetching https://mirror.spack.io/bootstrap/github-actions/v0.1/build_cache/darwin-catalina-x86_64/apple-clang-12.0.0/clingo-bootstrap-spack/darwin-catalina-x86_64-apple-clang-12.0.0-clingo-bootstrap-spack-p5on7i4hejl775ezndzfdkhvwra3hatn.spack
==> Installing "clingo-bootstrap@spack%apple-clang@12.0.0~docs~ipo+python build_type=Release arch=darwin-catalina-x86_64" from a buildcache
[ ... ]

triggers the bootstrapping of clingo from pre-built binaries as expected.

The Bootstrapping store

The software installed for bootstrapping purposes is deployed in a separate store. Its location can be checked with the following command:

% spack bootstrap root

It can also be changed with the same command by just specifying the newly desired path:

% spack bootstrap root /opt/spack/bootstrap

You can check what is installed in the bootstrapping store at any time using:

% spack find -b
==> Showing internal bootstrap store at "/Users/spack/.spack/bootstrap/store"
==> 11 installed packages
-- darwin-catalina-x86_64 / apple-clang@12.0.0 ------------------
clingo-bootstrap@spack  libassuan@2.5.5  libgpg-error@1.42  libksba@1.5.1  pinentry@1.1.1  zlib@1.2.11
gnupg@2.3.1             libgcrypt@1.9.3  libiconv@1.16      npth@1.6       python@3.8

In case it is needed you can remove all the software in the current bootstrapping store with:

% spack clean -b
==> Removing bootstrapped software and configuration in "/Users/spack/.spack/bootstrap"

% spack find -b
==> Showing internal bootstrap store at "/Users/spack/.spack/bootstrap/store"
==> 0 installed packages

Enabling and disabling bootstrapping methods

Bootstrapping is always performed by trying the methods listed by:

$ spack bootstrap list
Name: github-actions-v0.2 TRUSTED

  Type: buildcache

  Info: 
    url: https://mirror.spack.io/bootstrap/github-actions/v0.2
    homepage: https://github.com/spack/spack-bootstrap-mirrors
    releases: https://github.com/spack/spack-bootstrap-mirrors/releases

  Description: 
    Buildcache generated from a public workflow using Github Actions.
    The sha256 checksum of binaries is checked before installation.
    

Name: github-actions-v0.1 UNKNOWN

  Type: buildcache

  Info: 
    url: https://mirror.spack.io/bootstrap/github-actions/v0.1
    homepage: https://github.com/spack/spack-bootstrap-mirrors
    releases: https://github.com/spack/spack-bootstrap-mirrors/releases

  Description: 
    Buildcache generated from a public workflow using Github Actions.
    The sha256 checksum of binaries is checked before installation.
    

Name: spack-install TRUSTED

  Type: install

  Info: 
    url: https://mirror.spack.io

  Description: 
    Specs built from sources downloaded from the Spack public mirror.

in the order they appear, from top to bottom. By default Spack is configured to try first bootstrapping from pre-built binaries and to fall-back to bootstrapping from sources if that failed.

If need be, you can disable bootstrapping altogether by running:

% spack bootstrap disable

in which case it’s your responsibility to ensure Spack runs in an environment where all its prerequisites are installed. You can also configure Spack to skip certain bootstrapping methods by untrusting them. For instance:

% spack bootstrap untrust github-actions
==> "github-actions" is now untrusted and will not be used for bootstrapping

tells Spack to skip trying to bootstrap from binaries. To add the “github-actions” method back you can:

% spack bootstrap trust github-actions

There is also an option to reset the bootstrapping configuration to Spack’s defaults:

% spack bootstrap reset
==> Bootstrapping configuration is being reset to Spack's defaults. Current configuration will be lost.
Do you want to continue? [Y/n]
%

Creating a mirror for air-gapped systems

Spack’s default configuration for bootstrapping relies on the user having access to the internet, either to fetch pre-compiled binaries or source tarballs. Sometimes though Spack is deployed on air-gapped systems where such access is denied.

To help with similar situations Spack has a command that recreates, in a local folder of choice, a mirror containing the source tarballs and/or binary packages needed for bootstrapping.

% spack bootstrap mirror --binary-packages /opt/bootstrap
==> Adding "clingo-bootstrap@spack+python %apple-clang target=x86_64" and dependencies to the mirror at /opt/bootstrap/local-mirror
==> Adding "gnupg@2.3: %apple-clang target=x86_64" and dependencies to the mirror at /opt/bootstrap/local-mirror
==> Adding "patchelf@0.13.1:0.13.99 %apple-clang target=x86_64" and dependencies to the mirror at /opt/bootstrap/local-mirror
==> Adding binary packages from "https://github.com/alalazo/spack-bootstrap-mirrors/releases/download/v0.1-rc.2/bootstrap-buildcache.tar.gz" to the mirror at /opt/bootstrap/local-mirror

To register the mirror on the platform where it's supposed to be used run the following command(s):
  % spack bootstrap add --trust local-sources /opt/bootstrap/metadata/sources
  % spack bootstrap add --trust local-binaries /opt/bootstrap/metadata/binaries

This command needs to be run on a machine with internet access and the resulting folder has to be moved over to the air-gapped system. Once the local sources are added using the commands suggested at the prompt, they can be used to bootstrap Spack.