On Linux, if the system crashes and Skype does not exit normally, you may receive the following error when you next try to launch Skype:

Another Skype instance may exist.

The brute force method to recover from this is to simply completely remove your .Skype directory.  However, if you do this, you will lose any Skype preferences, as well as any call history, stored voicemails, etc.  For many folks, this is not a problem, and removing the .Skype directory is the easiest way to get back online.  However, in my case, I like having all my Skype information, so this was not an option.

There are several documents on the web which recommend the following:

rm $HOME/.Skype/shared.lck $HOME/.Skype/<user>/config.lck

where <user> is replaced with your Skype username. If you try these steps and are still receiving the same error, try the following procedure:

First, make sure that skype is NOT running:

ps -ef | grep skype

Verify that skype is not running in the resulting list of processes. If it is running, make sure you choose the "Quit" option from the skype menu - simply closing the window is not adequate.

Once you are sure Skype is not running, move your current Skype installation aside:

mv $HOME/.Skype $HOME/.Skype.saved

Next, launch Skype as you normally would. You should be presented with the license agreement and then be able to login.

Note: This login may take from 30-60 seconds to complete.

If you were able to successfully login, now do a normal exit from Skype. You have now created a "valid" .Skype configuration.

As before, verify that Skype is not running:

ps -ef | grep skype

If you are certain that Skype is, once again, not running then remove the new user information:

cd $HOME/.Skype
ls

You should see:

<user> shared.lck shared.xml

where <user> is your Skype username. Now remove the newly create user information:

rm -rf <user>

again where you replace <user> in the above command with your Skype username that was shown in the previous step.

Now copy your original Skype user directory from your saved Skype settings:

cp -pr $HOME/.Skype.saved/<user> $HOME/.Skype

again where you replace <user> in the above command with your Skype username.

You should now be able to launch Skype normally, with all your settings restored!

I hope this tip helps someone!