Here’s how I backported the Ubuntu package for CMake 2.8.5 to natty, making it available in a Launchpad PPA. Instead of using apt-get source, debuild and dput manually I opted for the handy script backportpackage, which can be found in the ubuntu-dev-utils package.

It’s actually quite easy to backport an existing package using the standard developer tools – once you find out exactly how to do it, that is. Here’s my little HOWTO.

And beware: rarely things go well as in this case. Sometimes the package specification needs to be modified to make it work (for instance, packaging CMake 2.8.5 for lucid is not trivial at all, but that’s another story).

Launchpad

Launchpad (among other things) is a good platform for generating and publishing Ubuntu and Debian packages. It allows users to set up private package repositories (PPAs) and hosts a farm of build servers as well.

You first need to set up an account (for free) at this URL, as described here.

In order to create your first PPA, you’ll need to import your PGP key to Launchpad and sign the Ubuntu Code of Conduct. There is a nice tutorial on WikiHow if you like pictures.

So far so good. You can now create your first PPA by following the link on your home page, which is something like https://launchpad.net/~username. I would suggest to pick a meaningful short name for the URL (I chose backports for this one) instead of just ppa.

Setting up your system

Your local Ubuntu box needs to be configured (only once) before trying to backport packages. First install some prerequisites:

$ sudo apt-get install cowbuilder ubuntu-dev-tools

Then create the base folder which will be used to setup the chrooted environment in which the package will be built:

$ mkdir -p ~/pbuilder/
$ sudo cowbuilder --create --distribution natty --components "main restricted universe multiverse" --basepath=$HOME/pbuilder/natty-base.cow

If you have more than one PGP key in your local keyring (I do), you may also want to specify which one to use when signing packages. Just list your keys with gpg --list-keys, and copy the key id to /etc/devscripts.conf under the debsign stanza:

DEBSIGN_KEYID=FDCCCD6E

Last problem to avoid: the personal package builders cowbuilder and pbuilder must be allowed to preserve the environment when called using sudo. Create the file /etc/sudoers.d/pbuilders using the command

$ sudo visudo -f /etc/sudoers.d/pbuilders

and put the following two lines into it:

Cmnd_Alias PBUILDERS = /usr/sbin/pbuilder, /usr/sbin/cowbuilder
ALL ALL=(ALL) SETENV: PBUILDERS

All done. Let’s backport the package (finally).

Building and uploading the package

We’ll work in a temporary directory, so first create it.

$ mkdir -p ~/backports/cmake/natty

Now cd into it:

$ cd ~/backports/cmake/natty

You should test the package build before the submission to Launchpad; it can be done by running backportpackage with the -b option:

$ BASEPATH=~/pbuilder/natty-base.cow DEBEMAIL=bcandrea@gmail.com DEBFULLNAME="Andrea Bernardo Ciddio" backportpackage -B cowbuilder -b -s oneiric -d natty -w . cmake

A brief explanation of the options:

• BASEPATH=~/pbuilder/natty-base.cow: this tells cowbuilder where to find the base image for the chroot
• DEBEMAIL=bcandrea@gmail.com DEBFULLNAME="Andrea Bernardo Ciddio": those values will appear in the generated Debian package
• -B cowbuilder: select cowbuilder to create the package (pbuilder is the default)
• -b: build the package completely and generate .deb files
• -s oneiric -d natty: source and destination codenames, respectively
• -w .: use the current path as a local build directory

Now that everything seems to be working, the package can be uploaded to our freshly created PPA:

$ DEBEMAIL=bcandrea@gmail.com DEBFULLNAME="Andrea Bernardo Ciddio" backportpackage -s oneiric -d natty -u ppa:bcandrea/backports cmake

References

How-To: PPA with CMake! - A useful tutorial about PPAs (it’s not about packaging CMake itself, tough)

Personal Package Archives - Everything you always wanted to know about PPAs, but were too afraid to ask

Ubuntu packaging guide - The ultimate source of information about Ubuntu packages