How to restart a service if its dependent service is restarted

Question

A service (say bar.service) is dependent on another service (say foo.service), like below

bar's service file:

[Unit] After=foo.service Requires=foo.service ... 

If foo.service is restarted (either manually or due to a bug), how can bar.service be automatically restarted as well?

Answer 1

You can use PartOf.

[Unit] After=foo.service Requires=foo.service PartOf=foo.service 

From the systemd.unit man page:

PartOf=

Configures dependencies similar to Requires=, but limited to stopping and restarting of units. When systemd stops or restarts the units listed here, the action is propagated to this unit. Note that this is a one-way dependency — changes to this unit do not affect the listed units.