Scala sbt "(run-main-0) ... Nonzero exit code" in CI

sbt ran your main method and the program threw or exited non-zero. The (run-main-0) prefix marks the forked run thread; the real cause is the exception printed just above the sbt summary.

What this error means

sbt run fails with "[error] (run-main-0) <Exception>" followed by a stack trace, then "[error] Nonzero exit code returned from runner: 1".

sbt

[error] (run-main-0) java.lang.RuntimeException: DATABASE_URL is not set
[error] java.lang.RuntimeException: DATABASE_URL is not set
[error]   at com.example.Main$.main(Main.scala:11)
[error] Nonzero exit code returned from runner: 1

Common causes

The program threw at runtime

Compilation succeeded but main hit a runtime error - a missing env var, a failed connection, an unhandled exception.

The application called exit with a non-zero code

Code reached sys.exit(1) or a framework returned a failure status, which sbt surfaces as a nonzero runner exit.

How to fix it

Read the exception above the summary

Scroll up to the (run-main-0) line and its stack trace.
Fix the runtime cause it names (set the env var, handle the failure).
Re-run sbt run to confirm it exits zero.

Provide required runtime configuration

Supply the environment the program expects so main does not throw on startup.

.github/workflows/ci.yml

env:
  DATABASE_URL: postgres://localhost:5432/app_test

How to prevent it

Validate required configuration at startup with clear messages.
Set runtime env vars the application needs in the CI step.
Distinguish compile failures from runtime failures by reading the prefix.