systemd: Stop dependent service when main service crashes

user_8929185 0
Viewed 5039

(systemd version 229)

I have a primary service A, and a secondary service B. The primary A can run by itself. But service B cannot run correctly by itself: it needs A to be running (technically B can run, but this is what I want systemd to prevent). My goal: If A is not running, B should not run. Given that A and B are running, when A stops or dies/crashes, then B should be stopped.

How do I achieve this?

I get close by adding [Unit] items to b.service, using 

Requisite=A.service
After=A.service

The result of the above is that

  • B won't start unless A is running (good).
  • B is stopped when A is stopped (good).
  • However, if I kill A, service B continues to run (bad).

How can I fix this last behavior? Neither PartOf nor BindsTo seems to do the trick, but perhaps I don't have the right incantation of combinations of options? Its not clear to me from the man pages what options can be combined.

systemd.unit man page: https://www.freedesktop.org/software/systemd/man/systemd.unit.html Related: Systemctl dependency failure, stop dependent services

systemctl systemd service linux
3 Answers

To achieve your 3rd objective make use of PartOf keyword.

In B.service you need to add dependency on A under [Unit] section as below

[Unit]
..
..
PartOf=A.service

With this, whenever A is killed B shall also stop.

user_74495400

If you start Service A with Type=notify you may be able to achieve something if you terminate A with SIGINT or SIGTERM, you can actually handle that and send a message on $NOTIFY_FD to systemd, but that option is still not possible with SIGKILL. It's a bit involved but might be able to achieve what you want.

You should also consider making A Restart=always. This will at-least make sure that A will remain available and B won't keep giving out errors. When you kill A (outside systemd), there's no way for systemd to know that A was killed - especially if you do so with kill -9 (SIGKILL cannot be handled). . So one of the best way to handle that will be to make Service A, Restart=always.

user_28450440

You can use, Requires= or PartOf= or BindTo=

see this article for detail of their usage

user_78955030
Related