I try to execute it manually in terminal, but output error is:

/usr/lib/polkit-kde-authentication-agent-1

New PolkitAgentListener 0x55fbb15fdca0
Adding new listener PolkitQt1::Agent::Listener(0x7f34780396c0) for 0x55fbb15fdca0
Listener online
"Cannot create unix session: No session for pid 2809"

• (process:2809): CRITICAL **: 12:20:33.145: polkit_agent_listener_register_with_options: assertion 'POLKIT_IS_SUBJECT (subject)' failed
  "Cannot register authentication agent!"
  Authentication agent result: false
  Couldn't register listener!

i am guessing that none of the parabola devs have a system setup with KDE, much less openrc+KDE - this could take some experimenting

off-hand, i can say that you probably only want to have one polkit package installed - i probably does not matter which one (at least that is my experience with the ones ive used such as gnome-polkit and lxpolkit)

I am seeing similar errors, which may be related, in Mate (x86) with OpenRC. I have tried running two different polkit agents (Mate and Gnome) from the terminal and they both give similar errors:

(polkit-mate-authentication-agent-1:24207): dbind-WARNING **: 07:13:53.904: Couldn't register with
accessibility bus: Did not receive a reply. Possible causes include: the remote application did
not send a reply, the message bus security policy blocked the reply, the reply timeout expired, or 
the network connection was broken.
Cannot register authentication agent: GDBus.Error:org.freedesktop.PolicyKit1.Error.Failed: Cannot 
determine user of subject

Looks like it may be related to this question that looks like it was posted on Stack Exchange by Megver83 ~3 years ago. Maybe he knows something about it?

i have seen problems when there are two different polkits
installed - make sure that you have only one installed and reboot

i will assign this to megver to get his attention

Well, I was kind of noob in those times. I posted the solution as a comment:

I could solve my problem by using a display manager that supports consolekit (e. g. sddm-consolekit, lxdm-consolekit, mdm-nosystemd)

Nowadays, it means that you need to use a DM that supports elogind. In my case, I use sddm-elogind (I'll update it and move it to [nonsystemd] in some moment)

does LXDM have a problem with elogind? - seeing as LXDE is the default DE, we need to make sure that keeps working - i have actually joined the LXDE dev team recently, so i should be able to get important changes upstream with little trouble

bill-auger wrote:

does LXDM have a problem with elogind? - seeing as LXDE is the default DE, we need to make sure that keeps working - i have actually joined the LXDE dev team recently, so i should be able to get important changes upstream with little trouble

You mean the default DE of the graphical ISOs? that means nothing, plus, the OpenRC version starts a root session, so it doesn't need polkit

i was not asking about the ISOs - i wanted to be sure that and installed openrc/LXDE system does not have the same problem as this ticket - do we need a lxdm-elogind package ?

Thanks for your replies on this. I am currently using lightdm on my x86. I will firstly try the polkit agents in LXDE and see if I encounter similar issues. Then, I will try sddm-elogind with Mate and see if it helps.

Logging in to LXDE via lightdm, I straightaway get a popup error window saying:

GDBus.Error:org.freedesktop.PolicyKit1.Error.Failed: Cannot determine user of subject

If I try to run /usr/lib/polkit-gnome/polkit-gnome-authentication-agent-1 in a terminal, I get the same error as before. Also, if I open virt-manager (which needs polkit), it can't connect to Qemu.

I installed sddm-elogind and got it working. However, I have to report that in Mate I am still seeing the same error with the Gnome polkit agent.

bill-auger wrote:

i was not asking about the ISOs - i wanted to be sure that and installed openrc/LXDE system does not have the same problem as this ticket - do we need a lxdm-elogind package ?

I'd have to test an LXDE + OpenRC installation some day, hopefully soon

Megver83 so, polkit agent authentication is working for you on your OpenRC system?

Btw, here is a link to the bug report I have opened on the elogind github page.

Update: I have now resolved the issue I was having, thanks to some advice from one of the elogind devs (see the previously-linked github issue). For me, the problem was the PAM configuration files for the display manager. I changed some of the lines in /etc/pam.d/sddm-greeter and system-login as he suggested (substituting 'session optional pam_elogind.so' and disabling the systemd ones) and now the polkit agents can authenticate.

I'll be happy to provide the files or more details of what I did, if needed. SO glad I finally managed to resolve this ...