Linux Mint 19 x64 with Cinnamon
Whenever I try to install a .deb by double clicking the file and clicking "Install Package" on the Package Installer popup, I get the following error:
There seems to be a programming error in aptdaemon, the software that allows you to install/remove software and to perform other package management related tasks.
org.freedesktop.DBus.Error.NoReply: Message recipient disconnected from message but without replying.
I can run apt update and upgrade just fine. I think something went wrong with an install I did awhile back using dpkg from the command line. I cannot find any details about how to fix this. Any ideas?
EDIT: I also can't install things from the Software Manager GUI. I've tried reinstalling both mintinstall, mintupdate, and gdebi but my situation has not changed after doing so. Can't uninstall through the GUI either.
EDIT 2: I've found that I can't open synaptic from the menu. If I run synaptic-pkexec from the command line I get the following output:
Error checking for authorization com.ubuntu.pkexec.synaptic: GDBus.Error:org.freedesktop.DBus.Error.NoReply: Message recipient disconnected from message bus without replying
Which leads me to think my problem might have to do with policykit but I don't know enough about policykit. policykit-desktop-privileges seems to an aid for users in the admin or sudo groups that run common tasks as sudo for them automatically. When I double click a deb file and the gdebi-gtk no problem arises until it would normally ask for my sudo password.
How do I troubleshoot potential issues with policykit?
EDIT 3: The problem seems to be rooted in Policy Kit so I've edited the question. I have a stable install of Linux Mint 19 x64 on my laptop and have been comparing my desktop's behavior to the laptop. On my laptop I run pkexec nano and the UI pops up asking for my password for sudo and running nano when I give the password. On my server, where I'm having the problem, when I run pkexec nano instead of the UI popup I expect, I get the same output I get when running synaptic-pkexec (except it says com.ubuntu.pkexec.exec instead of synaptic).
From some googling it seems that the default policy kit is supposed to be /usr/lib/policykit-1-gnome/polkit-gnome-authentication-agent-1. When I run the file I get:
** (polkit-gnome-authentication-agent-1:13684): WARNING **: 10:10:40.701: Unable to register authentication agent: GDBus.Error:org.freedesktop.PolicyKit1.Error.Failed: An authentication agent already exists for the given subject
I'm not sure if there's a way to find what is the current authentication agent. I do have a service called polkit that's active and doesn't seem to be throwing any errors. I've checked the log in /var/log/auth.log but it doesn't contain any errors. When I do the above pkexec nano the log prints the following:
Aug 9 10:14:44 MyComputerName polkitd(authority=local): Registered Authentication Agent for unix-session:c2 (system bus name :1.56 [/usr/lib/policykit-1-gnome/polkit-gnome-authentication-agent-1], object path /org/gnome/PolicyKit1/AuthenticationAgent, locale en_US.UTF-8)
This feels like polkit-gnome-authentication-agent-1 is active and running but apparently improperly.
I also find it weird that I can run sudo apt update and get prompted for my password properly (and it executes properly when given the password). I thought polkit would be in charge of that and it seems broken.
