Debian – How to Check if a Virtual Package is Installed

aptdebiandependenciespackage-management

Some packages, have a Provides: header. For example, the package postfix on Debian Wheezy has Provides: mail-transport-agent.

The package mail-transport-agent which doesn't exist physically is considered as a "virtual" package.

How can I know, on a Debian based system, if a given virtual package is "installed" (or "provided")? Can I list every "provided" virtual package?

Hint: to list every existing virtual package, installed or not, do: aptitude search "~v"

Best Answer

To list packages providing mail-transport-agent: 

$ aptitude search '~Pmail-transport-agent'
p   citadel-mta                     - complete and feature-rich groupware server
p   courier-mta                     - Courier mail server - ESMTP daemon        
p   dma                             - lightweight mail transport agent          
p   esmtp-run                       - user configurable relay-only MTA - the reg
p   exim4-daemon-heavy              - Exim MTA (v4) daemon with extended feature
p   exim4-daemon-light              - lightweight Exim MTA (v4) daemon          
p   masqmail                        - mail transport agent for intermittently co
p   msmtp-mta                       - light SMTP client with support for server 
p   nullmailer                      - simple relay-only mail transport agent    
i   postfix                         - High-performance mail transport agent     
p   sendmail-bin                    - powerful, efficient, and scalable Mail Tra
p   ssmtp                           - extremely simple MTA to get mail off the s
p   xmail                           - advanced, fast and reliable ESMTP/POP3 mai

Make that aptitude search '~Pmail-transport-agent ~i' to only list installed packages (if any).

To list all virtual packages provided by currently installed packages: 

aptitude search '~Rprovides:~i ~v'

See the aptitude manual for an explanation of the search patterns.

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