At the lowest level of the Debian package management system is the dpkg command. This command can be tricky for novice Linux users, so the Advanced Package Tool, apt-get, a front-end program to the dpkg tool, makes management of packages even easier.
Note
A front-end program is a program that users can see and interact with.
Follow Along
Many of the package management commands require administrative access, so they will be prefaced with the sudo command. Use netlab123 as the password when prompted.
Installing Packages
Package files are commonly installed by downloading them directly from repositories located on Internet servers. The Debian repositories contain more than 65,000 different packages of software. Before installing a package, it is good practice to use the refresh the list of available packages using the apt-get update command.
sudo apt-get update
sysadmin@localhost:~$ sudo apt-get update [sudo] password for sysadmin: Ign file: amd64/ InRelease Ign file: amd64/ Release.gpg Ign file: amd64/ Release Reading package lists... Done
To search for keywords within these packages, you can use the apt-cache search command.
apt-cache search [keyword]
The keyword that is used should match part of the name or description of the package that is to be located. Multiple keywords can be used to further clarify the search; for example, the search term web server would provide better results than web or server.
To find packages associated with the cow keyword:
sysadmin@localhost:~$ apt-cache search cow cowsay - configurable talking cow
Once you've found the package that you want to install, you can install it with the apt-get install command:
sudo apt-get install [package]
sysadmin@localhost:~$ sudo apt-get install cowsay [sudo] password for sysadmin: Reading package lists... Done Building dependency tree Reading state information... Done Suggested packages: filters The following NEW packages will be installed: cowsay 0 upgraded, 1 newly installed, 0 to remove and 0 not upgraded. Need to get 0 B/18.5 kB of archives. After this operation, 90.1 kB of additional disk space will be used. Selecting previously unselected package cowsay. (Reading database ... 24313 files and directories currently installed.) Preparing to unpack .../cowsay_3.03+dfsg1-6_all.deb ... Unpacking cowsay (3.03+dfsg1-6) ... Processing triggers for man-db (2.6.7.1-1ubuntu1) ... Setting up cowsay (3.03+dfsg1-6) ...
Consider This
The cowsay command is a configurable talking cow! Use a word or phrase as an argument:
sysadmin@localhost:~$ cowsay 'NDG Linux Unhatched' _____________________ < NDG Linux Unhatched > --------------------- \ ^__^ \ (oo)\_______ (__)\ )\/\ ||----w | || ||
We recommend enclosing the argument in single quotes to prevent the shell from interpreting special characters.
Updating Packages
The apt-get install command can also update a package, if that package is installed and a newer version is available. If the package is not already on the system, it would be installed; if it is on the system, it would be updated.
Updating all packages of the system should be done in two steps. First, update the cache of all packages available with apt-get update. Second, execute the apt-get upgrade command and all packages and dependencies will be updated.
apt-get update
apt-get upgrade
sysadmin@localhost:~$ sudo apt-get update [sudo] password for sysadmin: Ign file: amd64/ InRelease Ign file: amd64/ Release.gpg Ign file: amd64/ Release Reading package lists... Done sysadmin@localhost:~$ sudo apt-get upgrade Reading package lists... Done Building dependency tree Reading state information... Done Calculating upgrade... Done 0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
Removing Packages
The apt-get command is able to either remove or purge a package. The difference between the two is that purging deletes all package files, while removing deletes all but the configuration files for the package.
An administrator can execute the apt-get remove command to remove a package or the apt-get purge command to purge a package completely from the system.
apt-get remove [package]
apt-get purge [package]
For example, to purge cowsay completely, execute the following command. Enter Y when prompted:
sysadmin@localhost:~$ sudo apt-get purge cowsay Reading package lists... Done Building dependency tree Reading state information... Done The following packages will be REMOVED: cowsay* 0 upgraded, 0 newly installed, 1 to remove and 0 not upgraded. After this operation, 90.1 kB disk space will be freed. Do you want to continue? [Y/n] y (Reading database ... 24377 files and directories currently installed.) Removing cowsay (3.03+dfsg1-6) ... Processing triggers for man-db (2.6.7.1-1ubuntu1) ...
