spack

name	spack
description	Guide for installing, configuring, and using Spack to build software on Isambard AI (BriCS) supercomputers (Isambard-AI Phase 1, Phase 2, Isambard 3 Grace, Isambard 3 MACS). Use this skill whenever a user asks about Spack on Isambard, setting up a Spack environment, using the buildit configuration repository, concretizing or installing Spack packages, adding the isamrepo repository, targeting neoverse_v2 or aarch64 with Spack, or troubleshooting Spack builds on Cray HPE systems with Slingshot 11. Also trigger for questions about building HPC software from source on Isambard, managing Spack environments, or using system compilers and MPI within Spack — even if the user doesn't explicitly say "Spack" but is clearly trying to build software with dependency management on Isambard.
compatibility	Isambard-AI and Isambard 3. Requires access to an Isambard login node and a Spack installation or clone.
metadata	{"author":"isambard-sc","version":"1.0","source_url":"https://docs.isambard.ac.uk/user-documentation/guides/spack/"}

Spack on Isambard

Spack is a package manager for building HPC software and its dependencies in a consistent, reproducible way, taking into account the target machine's architecture and interconnect.

Note: Not every package is guaranteed to be supported. Only configurations outlined here have been tested by BriCS. Known issues will be listed in the upstream docs as they are reported.

Prerequisites: Familiarity with modules, MPI, and system specs (especially the Slingshot 11 interconnect).

Critical Rules

• Install and run Spack only from a supported Spack clone and the BriCS buildit config.
• Set SPACK_DISABLE_LOCAL_CONFIG=true to avoid conflicts with local ~/.spack settings.
• Always source spack/share/spack/setup-env.sh before using spack.
• Always activate a Spack environment before running spack install, spack add, or spack env create.
• Match the Spack version to the buildit config branch.

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Architecture Notes by System

System	Architecture	Spack target
Isambard-AI Phase 1	aarch64 / NVIDIA Grace	neoverse_v2
Isambard-AI Phase 2	aarch64 / NVIDIA Grace	neoverse_v2
Isambard 3 Grace	aarch64 / NVIDIA Grace	neoverse_v2
Isambard 3 MACS	x86_64 (mixed)	zen3 or similar — build on the target node

Slingshot 11 (SS11) is the high-speed interconnect on all systems. The buildit config ensures correct dependencies are used to exploit it.

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Step 1 — Download Spack

Clone a stable release into your home or project directory. The --depth=2 flag limits download size (Spack has a long history):

git clone --depth=2 --branch=releases/v1.1 https://github.com/spack/spack.git

Cache conflicts: If you have used a previous version of Spack, $HOME/.spack can cause issues. Either delete/move it, or isolate caches per version:

export SPACK_USER_CACHE_PATH=$PWD/spack-cache

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Step 2 — Activate Spack

Source the setup script to make the spack command available:

. spack/share/spack/setup-env.sh

Verify it works and check the detected architecture:

spack arch
# linux-sles15-neoverse_v2   (Isambard-AI / Isambard 3 Grace)
# linux-sles15-zen3          (Isambard 3 MACS, approx.)

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Step 3 — Download the BriCS buildit Config

BriCS provides a configuration repository that pre-configures compilers, MPI, and libraries correctly for each system. Clone it alongside the spack directory:

git clone --depth 1 --branch=releases/v2.1 https://github.com/isambard-sc/buildit.git

You should now have two directories: spack/ and buildit/.

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Step 4 — Create a Spack Environment

Disable local user config to avoid conflicts, then create an isolated environment:

export SPACK_DISABLE_LOCAL_CONFIG=true   # add to .bash_profile to make permanent
spack env create --dir myenv
spack env activate ./myenv

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Step 5 — Initialise the Environment

Apply the BriCS-provided packages config for your specific system, then set common options:

Isambard-AI Phase 1

spack config add --file buildit/config/aip1/v1.1/packages.yaml

Isambard-AI Phase 2

spack config add --file buildit/config/aip2/v1.1/packages.yaml

Isambard 3 Grace

spack config add --file buildit/config/3/v1.1/packages.yaml

Isambard 3 MACS

spack config add --file buildit/config/macs3/v1.1/packages.yaml

Then apply the same common settings for all systems:

spack config add config:build_jobs:8
spack config add view:true
spack config add concretizer:unify:true
spack config add concretizer:reuse:false

Verify compilers were found:

spack compiler list
# Expect: cce, gcc (multiple versions), nvhpc on aarch64 systems
# MACS also shows: aocc (x86_64)

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Step 6 — Add the Isambard Package Repository (Optional)

The buildit repo provides extra packages and fixes not yet upstream in Spack:

spack repo add ./buildit/repo/v1.1/spack_repo/isamrepo
# ==> Added repo to config with name 'isamrepo'.

Browse all available packages with spack list.

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Step 7 — Add, Concretize, and Install Software

Add a package to the environment (does not install yet):

spack add osu-micro-benchmarks

Concretize — resolve all dependencies consistently:

spack concretize
# Shows the full resolved dependency tree targeting neoverse_v2

Review the concretized output. If it looks correct, install:

spack install
# Installs to spack/opt/spack/linux-sles15-neoverse_v2/
# Environment view created at ./myenv/.spack-env/view/

After install, reload the environment to ensure everything is on PATH:

spack env deactivate && spack env activate ./myenv

Verify the install:

which osu_latency
# ./myenv/.spack-env/view/libexec/osu-micro-benchmarks/mpi/pt2pt/osu_latency

spack find
# Shows installed packages with their target (e.g. neoverse_v2)

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Deactivating an Environment

spack env deactivate

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Quick Reference

Goal	Command
Activate Spack	. spack/share/spack/setup-env.sh
Check detected arch	spack arch
Disable local config	export SPACK_DISABLE_LOCAL_CONFIG=true
Create environment	spack env create --dir myenv
Activate environment	spack env activate ./myenv
Apply BriCS config	spack config add --file buildit/config/<system>/v1.1/packages.yaml
List compilers	spack compiler list
Add Isambard repo	spack repo add ./buildit/repo/v1.1/spack_repo/isamrepo
Browse packages	spack list
Add package to env	spack add <package>
Resolve dependencies	spack concretize
Install	spack install
List installed	spack find
Deactivate environment	spack env deactivate

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Key Points to Remember

• Always use the buildit config for the correct system — it wires up Slingshot 11 MPI, system compilers, and scientific libraries correctly. Skipping this and letting Spack build its own MPI will produce binaries that don't use the high-speed interconnect.
• view:true means installed binaries are symlinked into ./myenv/.spack-env/view/ and available on PATH without loading modules.
• concretizer:reuse:false forces fresh builds rather than reusing cached installs — recommended for correctness on Isambard.
• Isambard 3 MACS has mixed CPU types — build on the node that matches your target architecture.
• The spack/opt/ install tree is per-architecture (e.g. linux-sles15-neoverse_v2).

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Further Resources

• Spack documentation
• Spack tutorial
• Spack environments tutorial
• Spack FAQ
• buildit repository
• Isambard MPI guide
• Isambard modules guide