Jak funguje apt-get

Příkaz

sudo apt-get update

It updates the available software list on your computer.

Your computer has a list (like a catalog) that contains all the available software that the Ubuntu servers have available. But the available software and versions might change, so a "update" will hit the server and see what software is available in order to update its local lists (or catalogs).

Note that update is diferent from upgrade. Update, as mentioned above, will fetch available software and update the lists while upgrade will install new versions of software installed on your computer (actual software updates).

To actually upgrade your software (not "update" the lists), you execute the command

sudo apt-get upgrade

which is usually executed after an "update".

Více o něm v What does "sudo apt-get update" do?.