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

[Simon McVittie]

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.

-- 
Simon McVittie
Collabora Ltd. <http://www.collabora.com/>