So,I made my Ubuntu Live 16 GB Flash Drive. I plug it in,booting from it. Everything is ruing OK. I download any .deb package and open it with Ubuntu Software Manager as I'd usually do with a fresh install of Ubuntu. When I press Install in the opened Ubuntu Software window,it goes a bit of orange then shows "Waiting to install" on the left-sided ruing tasks,and then it goes back to the previous Install button in the Software window as I've just opened the .deb package,while the "Waiting to install" icon is on the bar as it never has gone from there in the meantime. Even if I finally manage to install the .deb,the related app won't be there as I search it.
