[systemd-devel] Possible confusion with socket activation and daemon own configuration

[Francis Moreau]

On 09/08/2015 07:48 PM, Simon McVittie wrote:
> On 08/09/15 13:55, Francis Moreau wrote:
>> On 09/08/2015 12:09 PM, Richard Maw wrote:
>>> I understood that the common configuration for socket activated sshd was to
>>> have a sshd.service for if you want it to always be running, and a pair of
>>> sshd at .service and sshd.socket.
>>
>> Ah no, with this design starting sshd.service should do the right thing
>> but that's because there're 2 different service unit files:
>> sshd at .service and sshd.service.
> 
> As far as I understand it, this duplication is present to give the
> sysadmin a choice between two ways to run sshd, depending on this
> particular ssh server's requirements.
> 
> If ssh access is frequently used or needs to work quickly (for instance
> as the primary way to log in and fix things), enabling sshd.service
> means it will start "eagerly", on boot. Debian and its derivatives
> enable this by default (if sshd is installed).
> 
> If ssh access is infrequently used, a sysadmin can disable sshd.service
> and enable sshd.socket instead. That means sshd will be started
> on-demand, which will take a bit longer (particularly if the reason to
> log in is that the server has hit performance problems), but reduces
> resource consumption until then. This would be appropriate if the reason
> for providing ssh access is as a rarely-used "developer console"
> analogous to Android's adb, for instance.
> 

Yes that's my understanding too.

But I guess that some services can't be instanciated for each request
and in this case, there can be only one service unit, I think. And if
it's the case starting the service in on-demand mode will prevent to
start the service unit file by its own (ie. not using the socket unit file).

Thanks.