Systemd Declaring a Service Dependency

Internal

• systemd Operations
• systemd Concepts

Overview

This example shows how to declare a dependency between httpd and network services - the system should not attempt to start httpd unless the network service are started, otherwise httpd won't find the network interfaces to bind to. For more details on concepts behind dependencies, see:

systemd dependencies

Procedure

Create a httpd systemd service configuration directory

This is only necessary if the unit file (ex: /usr/lib/systemd/system/httpd.service) does not already exits.

If it does not exist, create a directory:

/etc/systemd/system/httpd.service.d

Create a httpd systemd service configuration file that expresses the dependency

Create a /etc/systemd/system/httpd.service.d/http-extra.conf file with the following content:

[Unit]
Requires=network-online.target
After=network-online.target

⚠️ Wrong configurations used network.target. This is incorrect, it has to be network-online.target.

For more details on the structure of a systemd unit file, see the [Unit] section of a unit file.

Procedure 2

TODO: Document this, it worked expressing the haproxy dependency on named.

Declare the dependency directly on a service, in the dependent service unit file:

...
Requires=named.service
After=named.service
...

This also worked:

...
After=network-online.target sshd-keygen.service
Wants=sshd-keygen.service
...