The preferred way to report a bug is with the ubuntu-bug command. The ubuntu-bug tool gathers information about the system useful to developers in diagnosing the reported problem that will then be included in the bug report filed on Launchpad. Bug reports in Ubuntu need to be filed against a specific software package, thus the name of the package that the bug occurs in needs to be given to ubuntu-bug:

ubuntu-bug PACKAGENAME

For example, to file a bug against the openssh-server package, you would do:

ubuntu-bug openssh-server

You can specify either a binary package or the source package for ubuntu-bug. Again using openssh-server as an example, you could also generate the report against the source package for openssh-server, openssh:

ubuntu-bug openssh

The ubuntu-bug command will gather information about the system in question, possibly including information specific to the specified package, and then ask you what you would like to do with collected information:

ubuntu-bug postgresql

*** Collecting problem information

The collected information can be sent to the developers to improve the
application. This might take a few minutes.
..........

*** Send problem report to the developers?

After the problem report has been sent, please fill out the form in the
automatically opened web browser.

What would you like to do? Your options are:
  S: Send report (1.7 KiB)
  V: View report
  K: Keep report file for sending later or copying to somewhere else
  C: Cancel
Please choose (S/V/K/C):

The options available are:

The software package that provides the ubuntu-bug utility, apport, can be configured to trigger when applications crash. This is disabled by default, as capturing a crash can be resource intensive depending on how much memory the application that crashed was using as apport captures and processes the core dump.

Configuring apport to capture information about crashing applications requires a couple of steps. First, gdb needs to be installed; it is not installed by default in Ubuntu Server Edition.

sudo apt-get install gdb

See Package Management for more information about managing packages in Ubuntu.

Once you have ensured that gdb is installed, open the file /etc/default/apport in your text editor, and change the enabled setting to be 1 like so:

# set this to 0 to disable apport, or to 1 to enable it
# you can temporarily override this with
# sudo service apport start force_start=1
enabled=1

# set maximum core dump file size (default: 209715200 bytes == 200 MB)
maxsize=209715200

Once you have completed editing /etc/default/apport, start the apport service:

sudo start apport

After an application crashes, use the apport-cli command to search for the existing saved crash report information:

apport-cli

*** dash closed unexpectedly on 2010-03-11 at 21:40:59.

If you were not doing anything confidential (entering passwords or other
private information), you can help to improve the application by
reporting
the problem.

What would you like to do? Your options are:
  R: Report Problem...
  I: Cancel and ignore future crashes of this program version
  C: Cancel
Please choose (R/I/C):

Selecting Report Problem will walk you through similar steps as when using ubuntu-bug. One important difference is that a crash report will be marked as private when filed on Launchpad, meaning that it will be visible to only a limited set of bug triagers. These triagers will review the gathered data for private information before making the bug report publicly visible.