Using ubuntu apt-get package manager to install, remove packages, upgrade ubuntu / How to keep ubuntu always updated and clean

Update ubuntu package list

 $ sudo apt-get update

update is used to resynchronize the package index files from their sources. The indexes of available packages are fetched from the location(s) specified in /etc/apt/sources.list. For example, when using a Debian archive, this command retrieves and scans the Packages.gz files, so that information about new and updated packages is available. An update should always be performed before an upgrade or dist-upgrade. Please be aware that the overall progress meter will be incorrect as the size of the package files cannot be known in advance.

Upgrade all installed packages in current ubuntu distribution

 $ sudo apt-get upgrade

upgrade is used to install the newest versions of all packages currently installed on the system from the sources enumerated in /etc/apt/sources.list. Packages currently installed with new versions available are retrieved and upgraded; under no circumstances are currently installed packages removed, or packages not already installed retrieved and installed. New versions of currently installed packages that cannot be upgraded without changing the install status of another package will be left at their current version. An update must be performed first so that apt-get knows that new versions of packages are available.

Upgrading all softwares in current ubuntu distribution (smart way)

 $ sudo apt-get dist-upgrade

dist-upgrade in addition to performing the function of upgrade, also intelligently handles changing dependencies with new versions of packages; apt-get has a “smart” conflict resolution system, and it will attempt to upgrade the most important packages at the expense of less important ones if
necessary. The dist-upgrade command may therefore remove some packages. The /etc/apt/sources.list file contains a list of locations from which to retrieve desired package files. See also apt_preferences(5) for a mechanism for overriding the general settings for individual packages.

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Install new package in ubuntu

 $ sudo apt-get install package_name

install is followed by one or more packages desired for installation or upgrading. Each package is a package name, not a fully qualified filename (for instance, in a Debian system, apt-utils would be the argument provided, not apt-utils_1.2.26_amd64.deb). All packages required by the package(s) specified for installation will also be retrieved and installed. The /etc/apt/sources.list file is used to locate the desired packages. If a hyphen is appended to the package name (with no intervening space), the identified package will be removed if it is installed. Similarly a plus sign can be used to designate a package to install. These latter features may be used to override decisions made by apt-get’s conflict resolution system.

Remove individual package

 $ sudo apt-get remove package_name

remove is identical to install except that packages are removed instead of installed. Note that removing a package leaves its configuration files on the system.

 $ sudo apt-get autoremove

autoremove is used to remove packages that were automatically installed to satisfy dependencies for other packages and are now no longer needed.

Remove package and its all configuration files

 $ sudo apt-get purge package_name/string

purge is identical to remove except that packages are removed and purged (any configuration files are deleted too).

Remove all downloaded but not installed packages

 $ sudo apt-get clean

clean clears out the local repository of retrieved package files. It removes everything but the lock file from /var/cache/apt/archives/ and /var/cache/apt/archives/partial/.

 $ sudo apt-get autoclean

Like clean, autoclean clears out the local repository of retrieved package files. The difference is that it only removes package files that can no longer be downloaded, and are largely useless. This allows a cache to be maintained over a long period without it growing out of control.

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