Ubuntu – How to install Elementary’s Pantheon Mail client on Ubuntu (15.10)

I presume you are trying to install that package using sudo dpkg -i package, well, that normally leads to package dependency problems so normally I suggest the use of gdebi. If you have any problematic package remove it. You can check using sudo apt-get check. Now down to business:

sudo apt-get install gdebi-core

With that we have ready gdebi. Now if you use a 64-bit system you may like to install the 64-bit package, likewise with 32-bits.

Now here comes the funny stuff...

sudo gdebi graphviz_2.37.20140208.0545-1\~saucy_amd64.deb 
Reading package lists... Done
Building dependency tree        
Reading state information... Done
Building data structures... Done 
Building data structures... Done 
This package is uninstallable
Dependency is not satisfiable: libgd2-noxpm (>= 2.0.36~rc1~dfsg)|libgd2-xpm (>= 2.0.36~rc1~dfsg)

And here is where you stop. The reason is that the stable package depends on package that were dropped of Debian, ergo Ubuntu 13.10:

libgd2 (2.0.36~rc1~dfsg-6.1) unstable; urgency=low

  * Non-maintainer upload.
  * Support multi-arch: (closes: #652496)
    - Mark libgd2-xpm, libgd2-noxpm, libgd2-xpm-dev and libgd2-noxpm-dev
      as same.
    - Adjust d-shlibs and dh-buildinfo build-dependency.
  * Drop .la files.

 -- Bastian Blank   Sun, 13 May 2012 09:16:37 +0000

Those are dependencies of graphviz so they should change them to libgd2-xpm-dev and libgd2-noxpm-dev respectively. If that's the case, you should download the latest build instead 2.38 or later, which includes the correct dependencies.

I've managed to install elementary desktop by rebuilding ubuntu-extras-keyring locally on my system, like this:

mkdir somedir; cd somedir
sudo apt-get install -y debhelper
wget http://archive.ubuntu.com/ubuntu/pool/main/u/ubuntu-extras-keyring/ubuntu-extras-keyring_2010.09.27.{tar.gz,dsc}
tar -xf *.tar.gz
cd ubuntu-extras-keyring-2010.09.17
debuild -i -us -uc -b
sudo dpkg -i ../ubuntu-extras-keyring_2010.09.27_all.deb

After that, elementary-desktop will install, but will error out at the end because it depends on systemd-shim which is no longer needed nor wanted with 15.04 having a full SystemD implementation.

When it errors out, run

sudo dpkg --force-depends -r indicator-datetime
sudo apt-get purge unity-control-center unity-control-center-signon

and it should complete the installation.

I expect in the near future the Elementary folks will fix their repository to handle SystemD properly - Ubuntu 15.04 move to SystemD was done a few weeks before the official release and the Elementary guys probably didn't have time to adapt to that.

After installation, you can log out and see "Pantheon" in your display manager's session list, but if you try to log in you'd get just the blueprint paper styled Elementary "beta wallpaper". The problem is that the session starts Slingshot and Gala, but not WingPanel or Plank. Currently I'm using using Slingshot's ALT-F2 shortcut to open the launcher and run Plank and WingPanel manually (just type the name in all lowercase and hit ENTER).