COSMA-build.md

@@ -37,6 +37,37 @@ mpirun --map-by socket:PE=32 -np MY_NUMBER_OF_MPI_RANKS swift_mpi --my-fancy-swi
 
 (for 4 ranks per node with 32 threads each)
 
+### Installing Spack for SWIFT on Cosma's Grace-Hopper Nodes
+
+1. Install spack to cosma apps directory
+    - Follow [the Spack tutorial](https://spack-tutorial.readthedocs.io/en/latest/tutorial_basics.html)
+    - You should end up with a spack install in e.g. `/cosma/apps/<project>/<username>/spack`
+    - You will run out of disk space if you install Spack in your home directory
+    - Running Spack's `setup-env.sh` will fail due to Cosma providing an incompatible Python module by default. So unload Python first:
+```
+$ cat ~/load_spack_aarch64.sh
+    module unload python
+    source ~/spack/share/spack/setup-env.sh
+```
+    - Then you can source your Spack setup script and you should have access to the `spack` command.
+2. Create a Spack environment just for SWIFT. You can call your environment whatever you like. Here I call it `swift`.
+    ```
+    spack env create swift
+    spack env activate swift
+    ```
+3. Install required dependencies:
+    ```
+    spack install --add hdf5
+    ```
+4. You should now be able to compile and run swift as normal.
+
+#### Misc tips for SWIFT on Cosma Grace-Hopper
+
+Sometimes Spack struggles to load the right library environment variables. You may need to compile with:
+
+```
+LIBRARY_PATH=$LD_LIBRARY_PATH ./configure ...
+```
 
 ### Cosma 7