For SL6/CentOS6 install the EPEL repo and yum install git-annex. 

I was waiting for my backups to be done hence this article, as I was using
_git-annex_ to manage my files and I decided I needed to have
git-annex on a SL5 based machine. SL5 is just an opensource
clone/recompile of RHEL5.

I haven't tried to install the newer versions of Haskell Platform and
GHC in a while on SL5 to install git-annex. But the last time I checked
when GHC7 was out, it was a pain to install GHC on SL5.

However I have discovered that someone has gone through the trouble of
packaging up GHC and Haskell Platform for RHEL based distros.

* <http://justhub.org/download> - Packaged GHC and Haskell Platform
  RPM's for RHEL based systems.

I'm primarily interested in installing _git-annex_ on SL5 based
systems. The installation process goes as such...

First install GHC and Haskell Platform (you need root for these
following steps)

    $ wget http://sherkin.justhub.org/el5/RPMS/x86_64/justhub-release-2.0-4.0.el5.x86_64.rpm
    $ rpm -ivh justhub-release-2.0-4.0.el5.x86_64.rpm
    $ yum install haskell

The RPM's don't place the files in /usr/bin, so you must add the
following to your .bashrc (from here on you don't need root if you
don't want things to be system wide)

    $ export PATH=/usr/hs/bin:$PATH

Once the GHC packages are installed and are in your execution path, using
cabal to build git-annex just makes life easier, it
should install all the needed dependancies. See "minimal build with cabal
and stackage" in [[fromsource]] for instructions.