socket activation services fail to start with no config file

[Andreas Hasenack]

sssd 2.2.x includes new socket activated services, specifically:
sssd-autofs.socket
sssd-nss.socket
sssd-pac.socket
sssd-pam-priv.socket
sssd-pam.socket
sssd-ssh.socket
sssd-sudo.socket

The sssd package in both ubuntu and debian does not ship a default sssd.conf file, something with which the main sssd service can cope with. These socket service, however, seem to obtain a fallback in-memory config file and complain like this when started:

Aug 01 12:49:07 eoan-sssd2 sssd_check_socket_activated_responders[3012]: The nss responder has
been configured to be socket-activated but it's still mentioned in the services' line in /etc/sssd/sssd.conf.

And fail to start:
root@eoan-sssd2:~# systemctl status sssd-nss.socket
● sssd-nss.socket - SSSD NSS Service responder socket
   Loaded: loaded (/lib/systemd/system/sssd-nss.socket; enabled;
vendor preset: enabled)
   Active: failed (Result: exit-code) since Thu 2019-08-01 12:49:07
UTC; 16min ago
     Docs: man:sssd.conf(5)
   Listen: /var/lib/sss/pipes/nss (Stream)

Mailing list thread:

https://<email address hidden>/thread/OQZ525APQFZLH75LGV6QV5X2PUH23PET/

Here is the output you get when installing the sssd package: https://pastebin.ubuntu.com/p/c5hzb6CrBh/