Ubuntu Wiki

• Launchpad Entry: https://launchpad.net/distros/ubuntu/+spec/command-not-found-magic

• Created: Date(2005-11-04T23:14:14Z) by MichaelVogt

• Contributors: MichaelVogt, GustavoNiemeyer, DanielBurrows

• Packages affected: bash

Summary

The "command not found" message is not very helpful. If e.g. the unzip command is not found but it's available in a package, it would be very interesting if the system could tell that the command is currently not available, but installing a package would provide it.

Rational

Because ubuntu ships only with a single CD some commands that power-users expect are not installed (e.g. gcc, make).

Use cases

• John sees a tutorial of how to unzip a package using the unzip command, and tries to follow it. The needed package is not installed, so he gets a dialog saying that installing the mentioned package is needed.

Design

Bash has a "command_not_found" handler that is called in the interactive mode when a command is not found. The first argument is the command that is not found. We hook a custom python script into it that has a database (gdbm or similar) with the available commands as keys and some information (like a list of packages it is in) as value. This lookup needs to be fast. This information is assembled from various sources:

• from the Content-$arch file
• from a "by-hand" file to include additonal stuff (like acroread)

• a mirror with deb that are scanned for update-alternatives commands in

  • postinst

Implementation

The command_not_found handler is in bash, no code for the python script has been written yet..