How to set dbus/systemd as dependency in systemd unit

php editor Xiaoxin will introduce to you how to set DBus/Systemd as a dependency of the Systemd unit. DBus and Systemd are two commonly used tools in Linux operating systems. DBus is used for inter-process communication, while Systemd is responsible for system initialization and process management. Combining DBus and Systemd can achieve more efficient system management and resource scheduling. This article will explain in detail how to configure DBus as a dependency in the Systemd unit to help you better understand and apply the use of these two tools.

Question content

I have a small program written in go that uses the go-systemd library to interact with systemd through dbus.

The program itself is registered as a systemd unit and should be started on boot. When the program is running, the systemd unit status of multiple units will be queried regularly.

Now when I start the program manually, everything is fine. However, when systemd starts after a reboot, it will "hang", meaning it will not be able to query systemd unit status via dbus. I will receive the following message from the go-systemd library:

process org.freedesktop.systemd1 exited with status 1

Now when I restart the program it will immediately be able to query systemd units without errors. This leads me to assume that my program has faulty/misconfigured dependencies and therefore a race condition on startup, preventing the program from communicating with systemd via dbus.

Now I've put this together with a few other combinations, but it doesn't help:

Requires=dbus.service
After=dbus.service
Wants=org.freedesktop.systemd1

How do I need to configure my own systemd unit (of the go program) so that it can communicate with systemd via dbus immediately after reboot? What dependencies do I have to configure?

Workaround

It sounds like your program is trying to connect to the DBus Session bus by default since you say it works fine when you run it manually. When an application is launched from Systemd, it will run as root by default and has no session bus to connect to, so it will fail.

When a user logs in on a graphical terminal, the session bus is typically started on a per-login basis. It will not start by default when logging in from the terminal.

If this is the case, I can currently see you having two options:

1. Use the system bus instead of the session bus.
2. Create your own connected bus, different from session bus and system bus. The easiest way is to use dbus-launch to create a new bus that your application can connect to.

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