# 7. PID 1 and signals

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`docker stop` - and Kubernetes, on pod deletion - sends SIGTERM to PID 1, waits (10 s for Docker,
`terminationGracePeriodSeconds` for Kubernetes), then SIGKILLs. Spring Boot's graceful shutdown only
runs if the JVM receives that SIGTERM.

[`pid1-and-signals.txt`](output/pid1-and-signals.txt):

```
layered-jre            PID 1: java -jar application.jar                                  docker stop:   244 ms  exit code: 143  graceful-shutdown log lines: 1
shell-form             PID 1: /bin/sh -c java -jar /app/app.jar                          docker stop: 10160 ms  exit code: 137  graceful-shutdown log lines: 0
shell-form-alpine      PID 1: java -jar /app/app.jar                                     docker stop:   219 ms  exit code: 143  graceful-shutdown log lines: 1
shell-form-wrapper     PID 1: /bin/sh -c echo "starting revision $(date +%s)" && java -j docker stop: 10176 ms  exit code: 137  graceful-shutdown log lines: 0
```

- **Exec form** (`["java", "-jar", ...]`): the JVM is PID 1, SIGTERM arrives, graceful shutdown
  runs, exit code 143, a quarter of a second.
- **Shell form on `eclipse-temurin:25-jre`**: `/bin/sh` is dash (`/usr/bin/dash`). dash stays
  resident as PID 1 and does not forward SIGTERM. Docker waits the full 10 s and SIGKILLs: exit 137,
  no graceful shutdown, in-flight requests cut off.
- **The same shell form on the Alpine image works**, because `/bin/sh` there is BusyBox ash, which
  replaces itself with the last command of a `-c` string. The same Dockerfile line behaves
  differently depending on the base image - which is how "it works on my image" arguments start.
- **Any shell form with more than one command** keeps the shell as PID 1 regardless.

If you need a wrapper script, end it with `exec java ...`. Distroless removes the question: with no
`/bin/sh`, a shell-form `ENTRYPOINT` cannot even start.