Using Chapel on Raspberry Pi

This document describes how to run Chapel on a standalone Raspberry Pi, as well as multi-locale on a Raspberry Pi cluster.


As the Chapel compiler has modernized, the memory requirements to build it have grown. If you find you can’t build Chapel in the memory you have available on your system, please let us know.

Configuring for Raspberry Pi

To build Chapel with support for Raspberry Pi, set:

export CHPL_ATOMICS=locks

Clustering the Pis

If you have a working cluster already, you can forgo this section of the guide.

This section describes just one of several ways to set up a Pi cluster. This section assumes that the user has already equipped each Pi with an SD card flashed with the operating system of the users’ choice – for example, Raspberry Pi OS Lite (Legacy).

In order to cluster all of the nodes, we must set up password-less SSH. This guide borrows from MagPi.

  1. Connect all nodes via Ethernet

Connect each node to a network switch via Ethernet cables. For a cluster with only two nodes, you can connect the two nodes directly without the need for a network switch.

  1. For each node, set a static IP address in the same subnet.

In this example, we will use as our subnet. If your regular network uses this, choose something different like

sudo nano /etc/dhcpcd.conf

At the end of the file, add the lines:

interface eth0
static ip_address=

For each node, replace the last digit of the subnet with a new unique value, such as 2, 3, and so on. You should be able to ping each node – for example, from

  1. Generate SSH keys

On each node, generate an SSH key by running the command:

ssh-keygen -t rsa

Press RETURN for each prompt and do not create a passphrase when asked.

  1. Copy SSH keys to all nodes in the cluster

For each non-master node, run:


to copy that node’s SSH key to the master node. Once that has been done on all non-master nodes, copy the master node’s SSH key to all other nodes in the cluster by running the same command from the master node, using the IP addresses of the other nodes as the command argument.

  1. Set up a shared filesystem

In order for each node to reference the same Chapel executable, the executable must be stored in a shared filesystem that all of the nodes in the cluster have simultaneous access to. There are several ways to do this.

One way is to mount a flash drive and export it as a network file system to the other nodes in the cluster. The steps to achieve this are described in sections 4.1 to 4.3 from this Medium article.

Configuring for Multi-Locale Execution

For more in-depth information about GASNet or multilocale execution with Chapel, refer to the GASNet documentation and Multilocale Chapel Execution page, respectively.

Ensure that the Chapel tree is installed in the shared filesystem (or that the Chapel tree is built on each node in your cluster), each node is running the same version of Chapel, and that all nodes in the cluster have SSH access to each other.

Complete these steps on the master node of your cluster.

  1. Set Chapel to use GASNet for multilocale execution

Set the following environment variable:

  1. Set up GASNet environment variables

Set the following GASNet environment variables:

GASNET_SPAWNFN=S # Job spawn mechanism, where 'S' means ssh/rsh-based spawn
GASNET_MASTERIP= # IP address of master node in your cluster, eg.
GASNET_SSH_SERVERS= # Space-delimited list of server names, eg.

Running Multilocale Chapel Programs

  1. Move Chapel executable to shared directory

This is necessary if your Chapel executables are not output to the shared filesystem by default.


mv hello /clusterfs/
mv hello_real /clusterfs/
  1. Run the program

Run the program as you would any other multilocale program:

/clusterfs/hello -nl 2