Arch Linux

lafleur

Member

Registered: 2018-10-12

Posts: 1

systemd --user and pam - understanding the interaction

Hello everybody - my first question on this forum ! I made an effort for the title, could'nt figure anything more explicitely synthetic (ahem).

I am happily using my Arch system for quite some time now, and trying to understand it a bit better.

I noticed that systemd ships in Arch with a default /etc/pam.d/systemd-user, said to be used by systemd --user. This file sources /etc/pam.d/system-login, which I understand as "systemd --user gets started as a normal user login". In the latter file, there's a line that says

-session optional pam_system.so

Moreover, pam_system's man page says

On login, this module [...] ensures the following :
  [...]
  An instance of the system service user@.service, which runs the systemd user manager instance, is
           started.

Isn't it precisely systemd --user that is mentioned here ? In this case, how come this system doesn't loop forever at login, pam calling systemd --user, systemd --user calling pam, and so on ?

Any insights are welcome !