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docs(gateway): warn against custom ExecStopPost kill drop-in (restart loop) (#53903)

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A user-added systemd drop-in like ExecStopPost=/bin/kill -9 $MAINPID fires
on every stop, including clean restarts — it SIGKILLs the freshly spawned
gateway before it stabilizes and Restart=always respawns it, producing an
infinite restart loop (issue #23272). The unit Hermes installs already shuts
down cleanly via KillMode=mixed + KillSignal=SIGTERM with Restart=always +
RestartForceExitStatus, so no extra kill is needed. Document this as a danger
callout in the gateway service-management section.
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Teknium 2026-06-27 19:04:29 -07:00 • committed by GitHub
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website/docs/user-guide/messaging/index.md
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@ -435,6 +435,10 @@ journalctl -u hermes-gateway -f
Use the user service on laptops and dev boxes. Use the system service on VPS or headless hosts that should come back at boot without relying on systemd linger.
:::danger Don't add a custom `ExecStopPost` kill drop-in
The unit Hermes installs already shuts the gateway down cleanly with `KillMode=mixed` + `KillSignal=SIGTERM`, and uses `Restart=always` with `RestartForceExitStatus` so updates and `/restart` respawn correctly. Do **not** add a systemd drop-in such as `ExecStopPost=/bin/kill -9 $MAINPID` — `ExecStopPost` fires on *every* stop, including clean restarts, so it `SIGKILL`s the freshly spawned instance before it stabilizes and `Restart=always` immediately respawns it. The result is an infinite restart loop (and, on Telegram, a flood of restart messages). If you've added such a drop-in, remove it: `systemctl --user edit hermes-gateway` (or `sudo systemctl edit hermes-gateway` for a system service) and delete the `ExecStopPost` line, then `systemctl --user daemon-reload`.
:::
:::tip Headless VMs: user service + linger avoids root prompts
A system service needs root for every restart — including the automatic gateway restart at the end of `hermes update`. When `hermes update` runs as a non-root user, it tries passwordless `sudo systemctl`; if that's unavailable, it skips the restart and prints the manual `sudo systemctl restart hermes-gateway` command (it never blocks on an interactive password prompt).