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I performed a fresh install of Lubuntu 12.04 with minimal desktop, as described here.

To clarify, I did a command-line install from the Lubuntu alternative install disc, then I did an apt-get install --no-install-recommends lubuntu-desktop.

Everything is working fine, except that Synaptic will not run from the menu entry in the panel. I am not prompted for a password, and no window of any sort appears after clicking the menu entry. I installed lxshortcut to see what the shortcut was running, and the command is synaptic-pkexec. If I type this command into the "Run" menu, I get the same behavior (or lack thereof).

I can get Synaptic to open up just fine by typing gksudo synaptic at the "Run" menu. Also, if I run "synaptic-pkexec" from the terminal, then I am prompted for my password within the terminal, and after that Synaptic opens normally.

Can someone please suggest the right way to get Synaptic working? I could just change the menu entry to "gksudo synaptic", but I'm guessing that it's set to synaptic-pkexec for a reason. I have a vague understanding that this pkexec business has something to do with PolicyKit, but I don't really know what PolicyKit is or how to tell if something is broken with it.

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This was a bug in Ubuntu 11.10, same exact scenario... it's discussed here - ubuntuforums.org/showthread.php?t=1827093 Maybe running an update would resolve it? –  Corey Whitaker Jul 10 '12 at 14:20
Can you start synaptic from terminal ? If you can't , enter output in here. –  alireza.m Jul 10 '12 at 14:20
Thanks for the link. According to that thread, the bug was fixed in synaptic-0.75.2ubuntu6. Running "apt-cache policy synaptic" says I have 0.75.9ubuntu1 installed. "apt-get update && apt-get dist-upgrade" says I'm fully up to date. –  ven42 Jul 10 '12 at 15:05
Try re-installing Synaptic. –  tijybba Jul 10 '12 at 15:41
Just tried "apt-get install --reinstall synaptic". The process completed successfully, but it did not change the behavior of synaptic. The problem still exists, I'm afraid. –  ven42 Jul 10 '12 at 15:49
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1 Answer

up vote 1 down vote accepted

It turns out that I needed to install the policykit-1-gnome package. Once I installed this package and rebooted, Synaptic worked normally.

I installed the complete Lubuntu desktop in a VM for comparison with my minimal installation, and that's how I discovered what was missing. According to the package description:

PolicyKit-gnome provides a D-Bus session bus service that is used to bring up authentication dialogs used for obtaining privileges.

Obviously, without the described functionality, I was never going to get a GUI authentication prompt to open Synaptic.

synaptic is a dependency of the lubuntu-desktop metapackage, so it was installed by default in my minimal installation. Shouldn't policykit-1-gnome be a dependency of lubuntu-desktop as well, since Synaptic won't work without it? Do you think I should report a bug?

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Excellent work tracking down the cause of the problem! And yes, I think you should report this as a bug. My Lubuntu systems installed from the Lubuntu desktop CD don't have this problem; they probably come with policykit-1-gnome installed separately from any other packages. It's set to manually installed (and I didn't install it myself). If you report a bug, please update your answer with the bug link. –  Eliah Kagan Jul 12 '12 at 0:23
I'm getting this exact same problem running a minimal install of ubuntu using standalone compiz session with Unity. Thing is, I have policykit-1-gnome installed, but its still not working. –  thelaststud Aug 17 '12 at 10:52
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