I have the following issue with a fresh arch-linux installation: in KDE/plasma with SDDM neither su or sudo work. I tried to use them in both konsole and xterm. What does also not work is authentication after the screen locker starts (this means I cannot unlock the screen). Initial login with SDDM works. (So to "unlock" the session I have to restart the SDDM service).

If I switch to another session (using CTRL-F2, etc.) I can use su and sudo as expected there.

What I have tried so far is reinstalling 'pambase' and 'pam' and check the configuration for /etc/pam.d/system-auth:


auth      required  pam_unix.so     try_first_pass nullok
auth      optional  pam_permit.so
auth      required  pam_env.so

account   required  pam_unix.so
account   optional  pam_permit.so
account   required  pam_time.so

password  required  pam_unix.so     try_first_pass nullok sha512 shadow
password  optional  pam_permit.so

session   required  pam_limits.so
session   required  pam_unix.so
session   optional  pam_permit.so

And of course also /etc/pam.d/sddm:


auth        include     system-login
account     include     system-login
password    include     system-login
session     include     system-login

What might be interessting is the output of journalctl after calling su:

Apr 28 14:42:30 zenbook su[7401]: pam_unix(su:auth): authentication failure; logname=myuser uid=1000 euid=0 tty=pts/2 ruser=myuser rhost=  user=
Apr 28 14:42:32 zenbook su[7401]: FAILED SU (to root) myuser on pts/2

Or after calling 'sudo nano':

Apr 28 15:06:29 zenbook sudo[7542]: pam_unix(sudo:auth): authentication failure; logname=myuser uid=1000 euid=0 tty=/dev/pts/2 rfuser=myuser rhos
Apr 28 15:06:43 zenbook sudo[7542]: myuser : 3 incorrect password attempts ; TTY=pts/2 ; PWD=/home/myuser ; USER=root ; COMMAND=/usr/bin/nano

I don't know what further information would be helpful to resolve this issue. I would be happy to provide more information if required.

Note: I have also asked the question on the arch forum without getting a reply so far.


So far I think it is related to SDDM because I have the same issue for example in Enlitenment when run with SDDM. If I start however an X11 session without SDDM su and sudo work without problems.

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