Can I control a user systemd using 'systemctl --user' after sudo su - myuser?

Question

I have a service that I want to start with system startup. I have built a [email protected] definition for it as a template, because there could be many instances.

Defined in the root systemd, this works well, and starts and stops the service with the system. The service instance is installed with systemctl enable ap@inst1 as would be expected. Root is also able to start and stop the service without problems. The service runs in its own account (myuser), not root, controlled by User=myuser in the [email protected] template.

But I want user 'myuser' to be able to start and stop their own service, without compromising system security.

I switched to using a user systemd, and enabled lingering with loginctl enable-linger myuser. I then enable the service defined in the ~myuser/.config/systemd/user directory. The service now starts and stops cleanly with the system, as designed. If I log in to a terminal as 'myuser', systemctl --user start ap@inst1, and systemctl --user stop ap@inst1 both work perfectly.

However, if I log in as a different user (user2) and perform sudo su - myuser in a terminal, then systemctl --user commands now fail with error message "Failed to get D-Bus connection: no such file or directory".

How do I enable systemctl --user to work after a sudo su - myuser command to switch the user?

Answer 1

I found the answer on another site with further searches using different terms.

The solutions needed was to provide the shell with information to reach the correct DBUS for the user.

By adding the following environment variables to the shell before running systemctl --user, the DBUS problem is eliminated, and systemctl operates correctly.

export XDG_RUNTIME_DIR="/run/user/$UID" export DBUS_SESSION_BUS_ADDRESS="unix:path=${XDG_RUNTIME_DIR}/bus" 

To ensure that the DBUS_SESSION_BUS_ADDRESS is available in the sudo shell, I added the environment variables to ~/.bash_profile of the target userid. This requires that a login shell ( sudo su - myuser or sudo -l myuser) is created in order to create the correct environment.

Alternatively, add the creation of the environment variables to ~/.bashrc (or equivalent for other shells). The environment will then be established anew for all shell creations.