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The same windows appear as I switch on the computer. Like if I had selected "Save session for future logins" though I don't. I remember launching some GUI apps with sudo, can it be the source of the problem?
How can I fix it?
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This depends on what UI/windowmanager setup you're currently using. You indicated xubuntu, which appears to already have been answered at Xubuntu reopens last session applications even though it shouldn't
If so, please be sure to give that person their updoot. :D
