[pkg-dhcp-devel] Bug#792894: systemd unit files for isc-dhcp-server

[Terry Burton]

On 31 May 2016 at 14:53, Terry Burton <tez at terryburton.co.uk> wrote:
> On 27 May 2016 at 14:12, Marc Haber <mh+debian-bugs at zugschlus.de> wrote:
>> On Fri, May 20, 2016 at 02:03:08AM +0100, Terry Burton wrote:
<...snip...>
>>> A general problem that I've noticed which might cause us to modify the
>>> isc-dhcp-server.target approach is that the following commands will
>>> not have the expected effect:
>>>
>>> service isc-dhcp-server {start,stop,restart}
>>> systemctl {start,stop,restart} isc-dhcp-server
>>>
>>> (1) It doesn't appear as though you can invoke .target unit files
>>> using /usr/sbin/service. This'll drive some purists nuts!
>>
>> I think this is something on systemd upstream's agenda to make people
>> migrate to the new, vendor lock-in interface asap.
>>
>>> (2) Additionally, these commands as-is will actually invoke LSB
>>> compatibility and trigger the sys-v init script rather than the native
>>> isc-dhcp-server.target unit file.
>>
>> Ouch. I consider this a bug in Debian's systemd packaging.
>>
>>> (3) The packaging would need to do something ensure that the
>>> isc-dhcp-server init script (via LSB) and isc-dhcp-server.target unit
>>> are not both started at boot.
>>
>> If this is a common issue for packages shipping both a sysv init
>> script and systemd units, it's up to systemd in Debian to fix this IMO.
>
> .service overrides LSB cleanly whereas .target does not. .target seems
> to be a powerful mechanism for controlling groups of service units
> under a single unit of control but it's not clear (to me) that that is
> precisely the intention of the systemd folks... I'm see if I can raise
> consensus about this. If it is intended that target to works in this
> way then it is clear that /usr/sbin/service should be patched to allow
> .target to override LSB.

Okay, I've now seen this [1] which blesses target units as a mechanism
for multiple service unit control, and the related open issue
regarding propagation of reload actions from targets to services [2]
(which doesn't affect isc-dhcp-server).

So to make target units a first order citizen would require changes to
at init-system-helpers scripts [3] and systemd
(/lib/lsb/init-functions.d/40-systemd) [4].


[1] https://lists.freedesktop.org/archives/systemd-devel/2015-July/033628.html
[2] https://github.com/systemd/systemd/issues/710
[3] https://sources.debian.net/src/init-system-helpers/1.34/script/
[4] https://sources.debian.net/src/systemd/230-1/debian/extra/init-functions.d/40-systemd/