The apt-get command
The Advanced Package Tool (APT) is a command-line tool that is used for easy interaction with the dpkg packaging system. APT is the ideal method used for managing software within Debian-based Linux distributions, such as Ubuntu. It manages dependencies effectively, maintains large configuration files, and properly handles upgrades and downgrades to ensure system stability. On its own, dpkg does not handle dependencies properly. apt-get performs installations, package searches, updates, and many other operations for packages available to your system. Keeping packages up to date is extremely important, as using out-of-date packages can lead to security issues on your system. The apt-get utility requires root privileges, similar to the dpkg utility.
First, before we make it perform in any software installation, it's always best practice to update the package database. We should run the apt-get update for this:
root@ubuntu:/home/philip/Downloads# apt-get update
Get:1 http://security.ubuntu.com/ubuntu xenial-security InRelease [107 kB]
Hit:2 http://us.archive.ubuntu.com/ubuntu xenial InRelease
Get:3 http://security.debian.org/debian-security wheezy/updates InRelease [54.0 kB]
Get:4 http://us.archive.ubuntu.com/ubuntu xenial-updates InRelease [109 kB]
Ign:3 http://security.debian.org/debian-security wheezy/updates InRelease
Get:5 http://us.archive.ubuntu.com/ubuntu xenial-backports InRelease [107 kB]
Get:6 http://security.debian.org/debian-security wheezy/updates/main amd64 Packages [589 kB]
Get:21 http://us.archive.ubuntu.com/ubuntu xenial-updates/multiverse amd64 DEP-11 Metadata [5,964 B]
Get:22 http://us.archive.ubuntu.com/ubuntu xenial-backports/main amd64 DEP-11 Metadata [3,328 B]
Get:23 http://us.archive.ubuntu.com/ubuntu xenial-backports/universe amd64 DEP-11 Metadata [5,096 B]
Fetched 6,189 kB in 6s (1,031 kB/s)
Reading package lists... Done
root@ubuntu:/home/philip/Downloads#
Based on the preceding output, the first section will be Hit, Get, Ign. Now, Hit means that there is no change in the package version, and Get means that there is a new version available. Then Ign means that the package is being ignored. There are various reasons why you would see Ign, ranging from a package being too recent to there being an error in retrieving the file. Usually, the errors are harmless.
Now, before we install an application, we can search for it using the apt-cache command. Let's say that we want to install a messenger application. We can do this in the following way:
root@ubuntu:/home/philip/Downloads# apt-cache search messenger
adium-theme-ubuntu - Adium message style for Ubuntu
totem-plugins - Plugins for the Totem media player
ayttm - Universal instant messaging client
banshee-extension-telepathy - Telepathy extension for Banshee
droopy - mini web server to let others upload files to your computer
dsniff - Various tools to sniff network traffic for cleartext insecurities
ekg2 - instant messenger and IRC client for UNIX systems
ekg2-api-docs - instant messenger and IRC client for UNIX systems - API documentation
ekg2-core - instant messenger and IRC client for UNIX systems - main program
yate-qt4 - YATE-based universal telephony client
yowsup-cli - command line tool that acts as WhatsApp client
empathy-skype - Skype plugin for libpurple messengers (Empathy-specific files)
pidgin-skype - Skype plugin for libpurple messengers (Pidgin-specific files)
pidgin-skype-common - Skype plugin for libpurple messengers (common files)
pidgin-skype-dbg - Skype plugin for libpurple messengers (debug symbols)
root@ubuntu:/home/philip/Downloads#
Based on the preceding output, we can see that a wide range of messenger packages are available to be installed. If, for some reason, we wanted to see all the available packages, we could use the pkgnames option:
root@ubuntu:/home/philip/Downloads# apt-cache pkgnames | less
libdatrie-doc
libfstrcmp0-dbg
librime-data-sampheng
xxdiff-scripts
globus-xioperf
edenmath.app
libghc-ansi-wl-pprint-doc
libjson0
zathura-cb
root@ubuntu:/home/philip/Downloads#
We can see a variety of packages which we can install onto this system. We can also see a brief description of each package by specifying the correct package name:
root@ubuntu:/home/philip/Downloads# apt-cache search zathura-cb
zathura-cb - comic book archive support for zathura
root@ubuntu:/home/philip/Downloads# apt-cache search virtaal
virtaal - graphical localisation editor
root@ubuntu:/home/philip/Downloads# apt-cache search python-logbook
python-logbook - logging system for Python that replaces the standard library's module
python-logbook-doc - logging system for Python that replaces the standard library's module (doc)
root@ubuntu:/home/philip/Downloads#
Based on the preceding output, we can see the descriptions for various packages that we passed with the search option. We can also check the details of a package by using the show option:
root@ubuntu:/home/philip/Downloads# apt-cache show python-logbook
Package: python-logbook
Priority: optional
Section: universe/python
Source: logbook
Version: 0.12.3-1
Depends: python:any (<< 2.8), python:any (>= 2.7.5-5~)
Suggests: python-logbook-doc
Filename: pool/universe/l/logbook/python-logbook_0.12.3-1_all.deb
Size: 47896
MD5sum: 865ee97095b97f74e362ce3d93a26a9e
SHA1: 812b08f4e4e4dbcd40264a99fa4cd4dff4f62961
SHA256: 3091d5c491e54007da8b510a6f2e463b63f62364938c4f371406cb4511b6232c
Origin: Ubuntu
root@ubuntu:/home/philip/Downloads#
We can even filter this information to only look for dependencies. We should use the showpkg option for this:
root@ubuntu:/home/philip/Downloads# apt-cache showpkg python-logbook
Package: python-logbook
Versions:
0.12.3-1 (/var/lib/apt/lists/us.archive.ubuntu.com_ubuntu_dists_xenial_universe_binary-amd64_Packages) (/var/lib/apt/lists/us.archive.ubuntu.com_ubuntu_dists_xenial_universe_binary-i386_Packages)
Dependencies:
0.12.3-1 - python:any (3 2.8) python:any (2 2.7.5-5~) python-logbook-doc (0 (null))
Provides:
0.12.3-1 -
Reverse Provides:
root@ubuntu:/home/philip/Downloads#
We can also view the statistics for the cache on this system by using the stats option:
root@ubuntu:/home/philip/Downloads# apt-cache stats
Total package names: 73419 (1,468 k)
Total package structures: 113356 (4,988 k)
Normal packages: 84328
Total buckets in PkgHashTable: 50503
Unused: 11792
Used: 38711
Utilization: 76.6509%
Average entries: 2.92826
Longest: 15
Shortest: 1
Total buckets in GrpHashTable: 50503
Unused: 11792
Used: 38711
Utilization: 76.6509%
Average entries: 1.89659
Longest: 8
Shortest: 1
root@ubuntu:/home/philip/Downloads#
Now, we can download a package without installing it. For this, we can use the download option with apt-get:
root@ubuntu:/tmp# apt-get download zathura-cb
Get:1 http://us.archive.ubuntu.com/ubuntu xenial/universe amd64 zathura-cb amd64 0.1.5-1 [8,812 B]
Fetched 8,812 B in 0s (40.0 kB/s)
root@ubuntu:/tmp# ls | grep zathura
zathura-cb_0.1.5-1_amd64.deb
root@ubuntu:/tmp#
We can also install a package that has been downloaded. We need to specify the path with the apt-get command:
root@ubuntu:/tmp# apt-get install ./zathura-cb_0.1.5-1_amd64.deb
Reading package lists... Done
Building dependency tree
Reading state information... Done
You might want to run 'apt-get -f install' to correct these.
The following packages have unmet dependencies:
openssh-server:i386 : Depends: openssh-client:i386 (= 1:6.0p1-4+deb7u7)
Recommends: ncurses-term:i386
Recommends: openssh-blacklist:i386 but it is not installable
Recommends: openssh-blacklist-extra:i386 but it is not installable
openssh-sftp-server:i386 : Breaks: openssh-server (< 1:6.5p1-5)
Breaks: openssh-server:i386 (< 1:6.5p1-5)
E: Unmet dependencies. Try using -f.
root@ubuntu:/tmp#
Now, sometimes you may run into the problem seen in the previous example. The easiest way to fix this would be to rerun the apt-get command with the -f option, leaving out the package name:
root@ubuntu:/tmp# apt-get -f install
Reading package lists... Done
Building dependency tree
Reading state information... Done
Correcting dependencies... Done
The following packages were automatically installed and are no longer required:
Do you want to continue? [Y/n] y
Preconfiguring packages ...
(Reading database ... 241439 files and directories currently installed.)
Preparing to unpack .../openssh-server_1%3a7.2p2-4ubuntu2.4_i386.deb ...
Unpacking openssh-server:i386 (1:7.2p2-4ubuntu2.4) over (1:6.0p1-4+deb7u7) ...
Processing triggers for ufw (0.35-0ubuntu2) ...
Processing triggers for systemd (229-4ubuntu21.2) ...
Processing triggers for ureadahead (0.100.0-19) ...
Processing triggers for man-db (2.7.5-1) ...
Setting up openssh-server:i386 (1:7.2p2-4ubuntu2.4) ...
Setting up tftp:i386 (0.17-18) ...
root@ubuntu:/tmp#
There we go! As we can see, the installation was successful. This is what is so great about the apt-get utility: it finds the dependencies that are needed and offers to install them to fix the problem being reported. We can also install multiple applications simultaneously. We simply place each package name on the same line, separated by a space:
root@ubuntu:/tmp# apt-get install virtaal vsftpd
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following packages were automatically installed and are no longer required:
libllvm3.8 libpango1.0-0 libpangox-1.0-0 libqmi-glib1 linux-headers-4.4.0-21 linux-headers-4.4.0-21-generic linux-image-4.4.0-21-generic
linux-image-extra-4.4.0-21-generic
Use 'sudo apt autoremove' to remove them.
The following additional packages will be installed:
javascript-common libglade2-0 libjs-jquery libjs-sph
Do you want to continue? [Y/n] y
Get:1 http://us.archive.ubuntu.com/ubuntu xenial/main amd64 libglade2-0 amd64 1:2.6.4-2 [44.6 kB]
Get:2 http://us.archive.ubuntu.com/ubuntu xenial/main amd64 javascript-common all 11 [6,066 B]
Get:3 http://us.archive.ubuntu.com/ubuntu xenial/main amd64 libjs-jquery all 1.11.3+dfsg-4 [161 kB]
Get:4 http://us.archive.ubuntu.com/ubuntu xenial/main amd64 libjs-underscore all 1.7.0~dfsg-1ubuntu1 [46.7 kB]
Get:5 http://us.archive.ubuntu.com/ubuntu xenial-updates/main amd64 libjs-sphinxdoc all 1.3.6-2ubuntu1.1 [57.6 kB]
Get:6 http://us.archive.ubuntu.com/ubuntu xenial-updates/main amd64 libpq5 amd64 9.5.13-0ubuntu0.16.04 [78.7 kB]
Setting up virtaal (0.7.1-1) ...
Setting up python-iniparse (0.4-2.2) ...
Setting up vsftpd (3.0.3-3ubuntu2) ...
Processing triggers for libc-bin (2.23-0ubuntu10) ...
Processing triggers for systemd (229-4ubuntu21.2) ...
Processing triggers for ureadahead (0.100.0-19) ...
root@ubuntu:/tmp#
Great! So, now you can see the power of the apt-get utility in action. We can also upgrade all of the packages that are currently installed by using the upgrade option:
root@ubuntu:/tmp# apt-get upgrade
Reading package lists... Done
Building dependency tree
Reading state information... Done
Calculating upgrade... Done
The following packages were automatically installed and are no longer required:
The following packages were automatically installed and are no longer required:
libllvm3.8 libpango1.0-0 libpangox-1.0-0 libqmi-glib1 linux-headers-4.4.0-21 linux-headers-4.4.0-21-generic linux-image-4.4.0-21-generic
linux-image-extra-4.4.0-21-generic
Use 'sudo apt autoremove' to remove them.
The following packages have been kept back:
libegl1-mesa libgbm1 libgl1-mesa-dri libwayland-egl1-mesa libxatracker2
The following packages will be upgraded:
apt apt-transport-https apt-utils base-files cups cups-bsd cups-client cups-common cups-core-drivers cups-daemon cups-ppdc
63 upgraded, 0 newly installed, 0 to remove and 5 not upgraded.
Need to get 67.1 MB/160 MB of archives.
After this operation, 1,333 kB disk space will be freed.
Do you want to continue? [Y/n] y
root@ubuntu:/tmp#
Some output was omitted for brevity.
We can also remove some packages that were previously used, to ensure a particular package was installed correctly. In our case, if we rerun the upgrade option, we should see this:
root@ubuntu:/tmp# apt-get upgrade
Reading package lists... Done
Building dependency tree
Reading state information... Done
Calculating upgrade... Done
The following packages were automatically installed and are no longer required:
libllvm3.8 libpango1.0-0 libpangox-1.0-0 libqmi-glib1 linux-headers-4.4.0-21 linux-headers-4.4.0-21-generic linux-image-4.4.0-21-generic
linux-image-extra-4.4.0-21-generic
Use 'sudo apt autoremove' to remove them.
The following packages have been kept back:
libegl1-mesa libgbm1 libgl1-mesa-dri libwayland-egl1-mesa libxatracker2
0 upgraded, 0 newly installed, 0 to remove and 5 not upgraded.
root@ubuntu:/tmp#
We should use the autoremove option, as suggested, to free up some disk space:
root@ubuntu:/tmp# apt-get autoremove
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following packages will be REMOVED:
libllvm3.8 libpango1.0-0 libpangox-1.0-0 libqmi-glib1 linux-headers-4.4.0-21 linux-headers-4.4.0-21-generic linux-image-4.4.0-21-generic
linux-image-extra-4.4.0-21-generic
0 upgraded, 0 newly installed, 8 to remove and 5 not upgraded.
After this operation, 339 MB disk space will be freed.
Do you want to continue? [Y/n] y
(Reading database ... 244059 files and directories currently installed.)
Removing libllvm3.8:amd64 (1:3.8-2ubuntu4) ...
Removing libpango1.0-0:amd64 (1.38.1-1) ...
Removing libpangox-1.0-0:amd64 (0.0.2-5) ...
done
Processing triggers for libc-bin (2.23-0ubuntu10) ...
root@ubuntu:/tmp#
We can also free up disk space by using the clean option:
root@ubuntu:/tmp# apt-get clean
root@ubuntu:/tmp#
As we can see, the command ran very quickly.
We can also remove an application by using the remove option. This would remove the application but not the configuration:
root@ubuntu:/tmp# apt-get remove virtaal
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following packages were automatically installed and are no longer required:
javascript-common libglade2-0 libjs-jquery libjs-sphinxdoc libjs-underscore libpq5 libtidy-0.99-0 python-babel python-babel-localedata
python-bs4 python-cairo python-chardet python-dateutil python-diff-match-patch python-egenix-mxdatetime python-egenix-mxtools
python-enchant python-gi python-glade2 python-gobject python-gobject-2 python-gtk2 python-html5lib python-iniparse python-levenshtein
python-lxml python-pkg-resources python-psycopg2 python-pycurl python-simplejson python-six python-tz python-utidylib python-vobject
python-xapian translate-toolkit
Use 'sudo apt autoremove' to remove them.
The following packages will be REMOVED:
virtaal
0 upgraded, 0 newly installed, 1 to remove and 5 not upgraded.
After this operation, 3,496 kB disk space will be freed.
Do you want to continue? [Y/n] y
root@ubuntu:/tmp#
We would then run the autoremove option to clean up unnecessary packages.