inportb

(This tutorial will work for any Debian-based system, including Ubuntu.)

If you’ve ever wanted to save a list of software installed on a Debian box so that you could reinstall them later or on a different machine, this is how you do it. I’ve recently had to reinstall my system from scratch, and the following may help you as well.

Generate the Package List

Let’s first save the current package selection states:

$ dpkg --get-selections | grep -v deinstall > packagelist

Now we have a compact list of installed packages in a file called “packagelist”. Let’s store this so that we could retrieve it from our other Debian installation. Or we could email it to ourselves using mailx:

$ cat packagelist | mailx -s “packagelist” user@example.com

Reinstall the Packages

To restore our packages, let’s first restore the package selection states:

$ sudo apt-get update
$ sudo apt-get dist-upgrade
$ sudo dpkg --set-selections < packagelist

Now let’s actually install it all:

$ sudo apt-get -u dselect-upgrade

Restore the System

What if we wanted to restore our system to an earlier state by installing everything that’s on our list and uninstalling everything that’s not? We can do that too, but we need to be careful because this may entail a radical change. Before restoring our package selection states, we’re going to deselect every package, thereby marking them for uninstallation:

$ sudo dpkg --clear-selections
$ sudo dpkg --set-selections < packagelist

Now, every package not on our list has been deselected and everything on our list has been selected. Let’s commit the changes:

$ sudo apt-get -u dselect-upgrade

If we wanted to remove the configuration files of the uninstalled packages, we’d do the following instead:

$ sudo apt-get -u dselect-upgrade --purge

Please don’t forget to restore the package selection states before running apt-get, or the whole system would be uninstalled.

I hope this tip proves to be helpful!