Updates the list of available packages and their versions, but it does not install or upgrade any packages.
apt-get update
Upgrade :
Installs newer versions of the packages based on the updated list of available packages.
apt-get upgrade
After updating the lists, the package manager would know about available updates for the software already installed in a computer. This is why running update prior to upgrade is recommended.
Raiyan - No upgrade would be possible without first updating the package database; so it is no so much "recommended" as much as "necessary". I usually perform this action:
ReplyDeletesudo apt-get update && sudo apt-get upgrade
There are complexities involved in the apt-get upgrade command that could impact dependencies and recommended packages, but those may be depreciated by now ("dist-upgrade" and "full-upgrade" come to mind).