sdnotify-wrapper-py 1.0.0

Notify readiness to systemd by writing to stdout in a service

sdnotify-wrapper-py

This project provides a command line tool sdnotify-wrapper, that can be used to send a readiness notification from a service to systemd, by simply writing a newline to stdout. This can be an alternative to sd_notify(3) or systemd-notify(1), if you don't want your service to depend on systemd.

Installation

There's a package published on PyPi, so it can be installed either with pip, or globally with pipx:

$ sudo PIPX_HOME=/opt/pipx PIPX_BIN_DIR=/usr/local/bin pipx install sdnotify-wrapper-py

Usage

In your service write one line to stdout whenever the service is ready (make sure to write logs to stderr instead). For example in Python (characters other than a newline are ignored):

print("ready", flush=True)

Or in C:

write(1, "\n", 1)

Then create a systemd service file with Type=notify, e.g. if your service would be started with my-service --foo bar:

[Unit]
Description=My Service

[Service]
Type=notify
NotifyAccess=all
ExecStart=/usr/local/bin/sdnotify-wrapper my-service --foo bar

[Install]
WantedBy=multi-user.target

sdnotify-wrapper will then connect to the stdout of your service, notify systemd when it reads a newline and exit.

Why Python?

sdnotify-wrapper is a tool originally written by Laurent Bercot: sdnotify-wrapper.c. Unfortunately this tool is not packaged for any of the major Linux distributions, so it's not a great user experience if your service requires this mechanism.

I chose to reimplement this tool in Python mainly, because it's easier to install it with a Python package manager. In doing this, I hope this readiness notification mechanism will be adopted by more projects and the original tool will be packaged by more distributions.