====== Ubuntu - Packages - List all packages installed on the system ======

Issue the command:

<code bash>
dpkg -l
</code>

Depending on the amount of packages on your system, this can generate a large amount of output.  Pipe the output through grep to see if a specific package is installed:

<code bash>
dpkg -l | grep apache2
</code>

Replace apache2 with any package name, part of a package name, or other regular expression.

----

<code bash>
dpkg --get-selections | grep -v deinstall
</code>