Which file contains the environment variables for systemd services?

The file that contains the environment variables for systemd services is not actually a service unit file like "foobar.service."

Instead, environment variables for systemd services are typically specified in "environment.conf" or similar configuration files associated with systemd. These files allow administrators to set environment variables that can be accessed by services managed by systemd.

For systemd units, these environment variables can also be configured directly within the service unit files themselves by using directives such as Environment= or by specifying an environment file with the EnvironmentFile= directive.

In this context, it's important to recognize that service unit files (like "foobar.service") primarily define how a specific service should be started, stopped, and managed, rather than serving as a centralized configuration for environment variables.