Use systemd service and timer to upload katello tracer

[sbernhard]

Instead of using cron, use systemd service and timer to upload the katello tracer. This is modern solution which is also supported by SUSE Micro distribution (which does not deliver a cron daemon)

[sbernhard]

Requires Katello/katello-host-tools#171 to be merged first.

[adamruzicka]

With cron, you just drop a file to a location and you're done. With systemd timers, you drop the unit definitions, but you then have to enable them. How would that be handled?

[sbernhard]

I'm not sure as I'm not yet able to fully test this but I have expected that the %systemd_post macro does enable the service. Need to verify this.

[dgoetz]

Yes, but you need also the timer installed and enabled so katello-tracer-upload.{service,timer} would be the shortest option. The macros install the unit with the preset, so enabled/disabled depends on this.

[sbernhard]

AFAIK, only the timer need to activated. I adapted the spec file accordingly. but actually, I can only fully test it if Katello/katello-host-tools#171 is merged.
See https://documentation.suse.com/en-us/sle-micro/6.0/html/Micro-systemd-working-with-timers/index.html and

[ogajduse]

[test rpm]

[ianballou]

katello-host-tools 4.6.0 is ready for packaging https://github.com/Katello/katello-host-tools/releases/tag/4.6.0

[sbernhard]

Packaging done @ianballou

[ogajduse]

I checked how Fedora packages (logrotate, plocate, fstrim) handle systemd timers in their specs, and have a few notes.

[ogajduse]

%systemd_preun already expands to systemctl disable --now when $1 == 0 (via systemd-update-helper remove-system-units). The manual call duplicates the same operation. Safe to remove the if block:

%preun tracer
%pkg_systemd_preun katello-tracer-upload.timer

[ogajduse]

Fedora convention is to pass both units so both get proper lifecycle handling:

%post tracer
%pkg_systemd_post katello-tracer-upload.service katello-tracer-upload.timer

%preun tracer
%pkg_systemd_preun katello-tracer-upload.service katello-tracer-upload.timer

%postun tracer
%pkg_systemd_postun katello-tracer-upload.service katello-tracer-upload.timer

For reference, logrotate does: %systemd_post logrotate.{service,timer}
https://src.fedoraproject.org/rpms/logrotate/blob/rawhide/f/logrotate.spec#_91

[ogajduse]

Suggested change

	%if 0%{?suse_version}
	%define pkg_systemd_post() %service_add_post %{*}
	%define pkg_systemd_preun() %service_del_preun %{*}
	%define pkg_systemd_postun() %service_del_postun %{*}
	%else
	%define pkg_systemd_post() %systemd_post %{*}
	%define pkg_systemd_preun() %systemd_preun %{*}
	%define pkg_systemd_postun() %systemd_postun %{*}
	%endif
	%if 0%{?suse_version}
	%define pkg_systemd_post() %service_add_post %{*}
	%define pkg_systemd_preun() %service_del_preun %{*}
	%define pkg_systemd_postun() %service_del_postun %{*}
	%define pkg_systemd_postun_with_restart() %service_del_postun %{*}
	%else
	%define pkg_systemd_post() %systemd_post %{*}
	%define pkg_systemd_preun() %systemd_preun %{*}
	%define pkg_systemd_postun() %systemd_postun %{*}
	%define pkg_systemd_postun_with_restart() %systemd_postun_with_restart %{*}
	%endif

On Fedora, %systemd_postun expands to literally nothing (verified from /usr/lib/rpm/macros.d/macros.systemd). This means on package upgrade ($1 >= 1), the timer won't be restarted to pick up changes.

# From /usr/lib/rpm/macros.d/macros.systemd on Fedora 43:

%systemd_postun() \
%{expand:%%{?__systemd_someargs_%#:%%__systemd_someargs_%# systemd_postun}} \
%{nil}

%systemd_postun_with_restart() \
%{expand:%%{?__systemd_someargs_%#:%%__systemd_someargs_%# systemd_postun_with_restart}} \
if [ $1 -ge 1 ] && [ -x "/usr/lib/systemd/systemd-update-helper" ]; then \
    # Package upgrade, not uninstall \
    /usr/lib/systemd/systemd-update-helper mark-restart-system-units %{?*} || : \
fi \
%{nil}

Compare with plocate which uses %systemd_postun_with_restart — that calls systemd-update-helper mark-restart-system-units, which sets a Markers=+needs-restart flag on the unit. The actual restart is then performed by a transfiletriggerin from the systemd package, which runs systemd-update-helper system-reload-restart (daemon-reload + systemctl reload-or-restart --marked) whenever files in /usr/lib/systemd/system/ are added or updated.

For the SUSE compat wrapper this would need a corresponding %service_del_postun_with_restart or equivalent — worth checking if SUSE has one, or whether a manual systemctl try-restart is needed there.

Two real-world examples from Fedora rawhide:

plocate (src):

%postun
%systemd_postun_with_restart plocate-updatedb.service plocate-updatedb.timer

util-linux / fstrim (src):

%postun
%systemd_postun_with_restart fstrim.timer
%systemd_postun fstrim.service

Note util-linux uses _with_restart on the timer but plain %systemd_postun (no-op) on the service — they want the timer restarted on upgrade but don't care about restarting the one-shot service itself. Reasonable pattern for katello-tracer-upload too since it's also a one-shot triggered by timer.

[ogajduse]

Same as for the above postun macro

Suggested change

	%postun tracer
	%pkg_systemd_postun katello-tracer-upload.timer
	%endif
	%postun tracer
	%pkg_systemd_postun_with_restart katello-tracer-upload.timer
	%pkg_systemd_postun katello-tracer-upload.service
	%endif

SUSE %service_del_postun may already do restart (their macros may behave differently from Fedora). If so, the SUSE wrapper for _with_restart mapping to plain %service_del_postun is correct. But needs someone with SUSE access to verify.