[systemd-devel] systemd-nspawn --setenv=SOMETHING=other: What is that for?

[Tobias Hunger]

Hi Systemd List!

I have been trying today to pass some information into a container I
set up with systemd-nspawn, using --setenv=SOMEVAR=foo. That works, I
see SOMEVAR in /proc/1/environ of the container.

So far so good.

Now I want to use that information to configure a service, so I add a
script that does the necessary configuration as a ExecStartPre-step to
a service file. This script takes the environment variables and puts
them into a configuration file for the service.

Unfortunately systemd does sanitize the environment before that script
is started. That is actually a good thing that saved my hide before,
but how can I make systemd export the necessary variable to that one
unit that needs it this one time?

The documentation on Environment in the service unit states that there
is no variable expansion going on. And just as documented

Environment=SOMEVAR

does not work. Neither does

Environment="SOMEVAR=$SOMEVAR"

At least there is no surprise there.

DefaultEnvironment in system.conf does export this variable to
everybody. Do I need to do that?

The documentation on DefaultEnvironment also makes no mention of
passing variables already set in PID1 on to other processes. It seems
to be about adding new variables, just as Environment and
EnvironmentFile in the service units.

Any idea how I can run trigger a script that see SOMEVAR as seen by PID1?

Thanks,
Tobias