While working on the instructions for compiling MonoDevelop from source, I relied heavily on the dpkg and apt-cache commands to tell me what was already installed vs what packages were available in the repository. After completing that article it occurred to me that I should explain how to show what packages are currently installed… so here we are.

The command we need to use is dpkg –get-selections, which will give us a list of all the currently installed packages.

$ dpkg --get-selections
adduser                                         install
alsa-base                                       install
alsa-utils                                      install
apache2                                         install
apache2-mpm-prefork                             install
apache2-utils                                   install
apache2.2-common                                install
apt                                             install
apt-utils                                       install

The full list can be long and unwieldy, so it’s much easier to filter through grep to get results for the exact package you need. For instance, I wanted to see which php packages I had already installed through apt-get:

dpkg --get-selections | grep php
libapache2-mod-php5                             install
php-db                                          install
php-pear                                        install
php-sqlite3                                     install
php5                                            install
php5-cli                                        install
php5-common                                     install
php5-gd                                         install
php5-memcache                                   install
php5-mysql                                      install
php5-sqlite                                     install
php5-sqlite3                                    install
php5-xsl                                        install

For extra credit, you can find the locations of the files within a package from the list by using the dpkg -L command, such as:

dpkg -L php5-gd
/.
/usr
/usr/lib
/usr/lib/php5
/usr/lib/php5/20060613
/usr/lib/php5/20060613/gd.so
/usr/share
/usr/share/doc
/etc
/etc/php5
/etc/php5/conf.d
/etc/php5/conf.d/gd.ini
/usr/share/doc/php5-gd

Now I can take a look at the gd.ini file and change some settings around…

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Lowell is the founder and CEO of How-To Geek. He’s been running the show since creating the site back in 2006. Over the last decade, Lowell has personally written more than 1000 articles which have been viewed by over 250 million people. Prior to starting How-To Geek, Lowell spent 15 years working in IT doing consulting, cybersecurity, database management, and programming work.
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