No, pkexec per default does not start a graphical application for security reasons. If you want to start a graphical application with pkexec, you need a policy in /usr/share/polkit-1/actions.
But, nowadays, it mostly isn't necessary to start a graphical application with elevated privileges, because there are better alternatives. On *buntu 18.04, synaptic does have a policy => https://packages.ubuntu.com/bionic/amd64/synaptic/filelist You can start it with synaptic-pkexec. The same command is used in /usr/share/applications/synaptic.desktop If it does not work and you have a policy, please check, that the PolicyKit Authentication Agent is running (lxsession-default-apps in section autostart) and logout/login. I don't understand, how "su -l $other_user" is related to this bug report? -- You received this bug notification because you are a member of Ubuntu Touch seeded packages, which is subscribed to policykit-1 in Ubuntu. https://bugs.launchpad.net/bugs/1288786 Title: pkexec does not launch graphical authentication Status in policykit-1 package in Ubuntu: Confirmed Bug description: Installed Trusty Tahr Lubuntu Beta1 version and added xubuntu desktop. In buth desktops, I tried to launch synaptic to install some packages. If I try to launch from menu, nothing seems to happen. From a terminal, I ran pkexec "/usr/sbin/synaptic" and saw that it asks for password in the terminal window, instead of popping up an authentication window like previous Ubuntu version did. That was why I saw no authentication request when launching from menu.. I have a workaround)launching from Terminal window), but this should be fixed before release. ralph@minnie:~$ cat /etc/lsb-release DISTRIB_ID=Ubuntu DISTRIB_RELEASE=14.04 DISTRIB_CODENAME=trusty DISTRIB_DESCRIPTION="Ubuntu Trusty Tahr (development branch)" ralph@minnie:~$ pkexec --version pkexec version 0.105 Thanks To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/policykit-1/+bug/1288786/+subscriptions -- Mailing list: https://launchpad.net/~touch-packages Post to : firstname.lastname@example.org Unsubscribe : https://launchpad.net/~touch-packages More help : https://help.launchpad.net/ListHelp