The Software Center won't start anymore, how to fix it?

I have been using Ubuntu 13.04 for last 2 months. It was working properly but suddenly the Ubuntu Software Center has started hanging. Now it doesn't open. And every time I try to open it, I have to force quit it. So that I am not able to install the software that I need. What do I do?

Make sure software-center is not running.

First make sure the Software Center (process name software-center) is not running. Depending on how you've been forcing it to quit, a software-center process may or may not still be running in the background.

If you know how to make sure a process isn't running, you can skip the rest of this section.

You can use the GNOME System Monitor for this (type system monitor in the Unity dash and an icon for GNOME System Monitor will appear).

Or you can use killall from the Terminal (Ctrl+Alt+T):

killall software-center

Run it again and you should get:

software-center: no process found

If you don't see that, it's still running. In that case, run:

killall -KILL software-center

(Running that again will, in the same way, determine if it succeeeded)

The Software Center is not ordinarily run as root: instead, it uses polkit to perform specific actions as root. But if it is running as root, then you'll have to put sudo before a killall command for it to succeed.

Clear out both user-specific and systemwide configuration files and reinstall USC.

Open a Terminal window (Ctrl+Alt+T) if you don't already have one open. Run these commands to remove user-specific configuration files:

cd ~/.config
mv software-center software-center.old

(This actually moves the configuration rather than deleting it, but it prevents it from being used. It's unlikely you'll need to restore it, but there's no major disadvantage.)

Then reinstall the Software Center, removing systemwide configuration files:

sudo apt-get update
sudo apt-get --purge --reinstall install software-center

Some errors that could interfere with the Software Center starting or working properly could also keep those commands from working. In particular, if you see an error that says Unable to lock the administration directory, check out the answers here:

• Unable to lock the administration directory (/var/lib/dpkg/) is another process using it?

Then try running the Software Center again.

If that doesn't work...

...then more information will be needed. Run the Software Center itself in the Terminal:

software-center

That may reveal messages (errors or otherwise) that would help solve the problem. You can edit your question to include all the text from the Terminal.

(Other people with this problem should create or edit their own questions, of course.)

One possible cause of this problem might be if polkit is not running, or not working properly. If you don't see any helpful messages when you run software-center in the Terminal, you might try running it as root:

gksudo software-center

If you don't have the gksudo command, you can install it (it's provided by the gksu package), or use sudo -H instead of gksudo.

If that doesn't work and you need a workaround to install software until the problem iss solved, see:

• Are there alternatives to software center?

In particular, Synaptic works very differently from the Software Center and is quite likely to work even when the Software Center does not. Synaptic does not provide the means to install paid apps, though.