3. piw-slave

The piw-slave script is intended to be run on a standalone machine to build packages on behalf of the piw-master script. It is intended to be run as an unprivileged user with a clean home-directory. Any build dependencies you wish to use must already be installed. The script will run until it is explicitly terminated, either by Ctrl+C, SIGTERM, or by the remote piw-master script.

3.1. Synopsis

piw-slave [-h] [--version] [-c FILE] [-q] [-v] [-l FILE] [-m HOST]
          [-t DURATION]

3.2. Description

-h, --help

Show this help message and exit


Show program’s version number and exit

-c FILE, --configuration FILE

Specify a configuration file to load

-q, --quiet

Produce less console output

-v, --verbose

Produce more console output

-l FILE, --log-file FILE

Log messages to the specified file

-m HOST, --master HOST

The IP address or hostname of the master server (default: localhost)


The time to wait before assuming a build has failed (default: 3h)

3.3. Deployment

Our typical method of deployment is to spin up a new Pi as a build slave (through Mythic Beasts’ control panel) then execute a script to install the piwheels code, and all the build dependencies that we feel are reasonable to support under various Raspbian versions. The deployment script can be found in the root of the piwheels repository:

# wget https://raw.githubusercontent.com/piwheels/piwheels/master/deploy_slave.sh
# chmod +x deploy_slave.sh
# ./deploy_slave.sh

However, you will very likely wish to customize this script for your own purposes, e.g. to support a different set of dependencies, or to customize the typical build environment.

Once the script is complete, simply switch to the unprivileged user used to run the build slave, and execute piw-slave. For example, assuming the master’s IP address is

# su - piwheels
$ piw-slave -m

3.4. Automatic start

If you wish to ensure that the build slave starts on every boot-up, you may wish to define a systemd unit for it. Example units can be also be found in the root of the piwheels repository:

# wget https://raw.githubusercontent.com/piwheels/piwheels/master/piwheels-slave.service
# cp piwheels-slave.service /etc/systemd/system/
# systemctl daemon-reload
# systemctl enable piwheels-slave
# systemctl start piwheels-slave


Be aware that this example unit forces a reboot in the case that the build slave fails (as occasionally happens with excessively complex packages).

Because of this you must ensure that the slave executes successfully prior to installing the unit, otherwise you’re liable to leave your build slave in permanent reboot cycle. This isn’t a huge issue for a build slave that’s physically in front of you (from which you can detach and tweak the storage), but it may be an issue if you’re dealing with a cloud builder.