Ubuntu – Is “sudo apt-get update” mandatory before every package installation

aptupdates

I know what the purpose of the update command is, and I was just wondering if i must use it before any package installation I perform. What if I have not update for too long and install some critical packages? Also, is there any occasion that there is no need to do that?

Best Answer

Your copy of Ubuntu has a private copy of the list of packages that are in Ubuntu's repositories. When you install a package, apt-get reads the list and determines the URL of the package to download (which typically contains package version information).

apt-get update updates the package lists. If you don't do it before an installation, apt-get might complain that it cannot find the package in the repository, because it computed the URL based on an old version of the list (which listed an older version of the package).

Of course, apt-get update is necessary after you have changed the repositories, because the system needs to download the list for the new repositories.

It is essential before upgrading the installed packages, because the system cannot know whether the repo has a new version of a package, unless it has an up-to-date copy of the package list.

There is no reason not to run apt-get update before installing a package. However, it is not necessary, if you know that no new version of that package and of its dependencies have been made available on the mirrors since the last apt-get update. A special case of this is when the package lists are up to date, which is after a reasonably short time since the last apt-get update; this means that all packages on the mirror are the same version as they were.

The package list changes whenever a package is upgraded on the mirror. It is impossible to predict how often it changes, in general, without reference to a specific issue or bug report, or without following the development of that Ubuntu release.

Related Question