Automatically enable systemd services installed using deb?

Actually, you don't need to add anything in override_dh_auto_install.

You need --with systemd (without the dash between with and systemd) in the rules and the package dh-systemd installed.

I've worked around the problem by calling dh_systemd_enable (to make the service run by default) and dh_systemd_start (to actually start it after installation) manually from the override_dh_auto_install target in rules, so it looks like this:

%:
    dh $@ --with-systemd

override_dh_auto_install:
    dh_auto_install
    dh_systemd_enable || true
    dh_systemd_start || true

I ran into this issue as well. It turns out that dh_systemd_enable has certain expectations about the content of a foo.service file.

You can see this in lines 187-215 of deb-systemd-helper.

In particular, ensuring that the foo.service file has an [Install] section and has at least an Alias field where the alias does NOT equal foo.service will cause the call to deb-systemd-helper enable to detect the needed service. If you want the service to be automatically started adding WantedBy=multi-user.target is also needed.

Below is a lightly modified version of my foo.service file:

[Unit]
Description=foo service, foos
After=bar.service
Requires=bar.service

[Service]
ExecStart=/path/to/my/script/foo
Restart=always
RestartSec=5

[Install]
Alias=foo
WantedBy=multi-user.target

I was able to determine this by enabling a couple debug flags and adding debug statements in the deb-systemd-helper perl script. On an Ubuntu 16.04 system I found it here: /usr/bin/deb-systemd-helper.

So repeatedly running the following and adding debug statements got me to the bottom of the problem.

$ sudo DPKG_MAINTSCRIPT_PACKAGE=1 _DEB_SYSTEMD_HELPER_DEBUG=1 deb-systemd-helper enable foo.service