Ubuntu 14.04 and higher

Open GIMP, and go to Windows > Single-Window Mode

Ubuntu 12.04

Single-Window Mode is only available since GIMP 2.8+. You will have to install GIMP 2.8 from a ppa if you want Single-Window Mode. Just follow the next instructions:

1. Add the GIMP PPA. Open the terminal and copy/paste the following command: sudo apt-add-repository ppa:otto-kesselgulasch/gimp && sudo apt-get update
2. Update GIMP using Update Manager or apt-get.
3. Open GIMP, and go to Windows > Single-Window Mode

Now you have a single window! For example, my GIMP main menu:

Here is how to compile the deskew plugin for Gimp. It is largely trouble free, but I will note certain important things as I go along. This should work across all Gimp 2.x versions; it has been tested successfully on Gimp versions 2.6 and 2.8.

Firstly, you need the Gimp development files, and the most important one is libgimp2.0-dev as it contains the header files necessary for compiling plugins for gimp.

sudo apt-get install libgimp2.0-dev

I already had the other gimp development files installed, as I had run sudo apt-get build-dep gimp, but you shouldn't need them for this one plugin.

Now pull the code from git with:

git clone git://github.com/prokoudine/gimp-deskew-plugin.git

Then cd to the gimp-deskew-plugin folder and run

./autogen.sh

I would normally specify --prefix=/usr here, as we don't want the plugin installed in /usr/local, however it doesn't install correctly in the /usr hierarchy, but I will explain how to overcome that later.

Now, run make and the plugin executable is compiled in a few seconds.

As running sudo make install doesn't quite get it to where we want it (even with specifying a prefix earlier), it is necessary in this case to manually copy the one executable to the Gimp plugins folder:

Cd to ~/gimp-deskew-plugin/src and run

sudo cp deskew /usr/lib/gimp/2.0/plugins

The plugin is now accessible from Gimp > Layer > Transform > Deskew.