Jekyll can be run fairly easily on older (5.x and 6.x) versions of RHEL/CentOS, even though the stock versions of the necessary software are too old. The key is to use some simple supporting software to install what you need in a clean way.
The first handy tool is Ruby Version Manager, or RVM. Here’s a handy cheat sheet – use that to install RVM and the latest version of Ruby, set the installed Ruby as the default, and install the Jekyll gem.
Once that’s done, you may run into this error when trying to use Jekyll:
Liquid Exception: Failed to get header
Use the pyenv installer to get pyenv set up and running on your server, and have a look at the pyenv command reference to install an appropriate version of Python and set it as the default. Note: If you’re running RHEL/CentOS 5.x, you’ll have one more hurdle to cross before using pyenv, see this post for detailed instructions.
If you’d also like to set up your Jekyll site to update from a git push, I’ve detailed one workable approach in this post – if you do use it, just make sure you put the necessary RVM/pyenv environment set up stuff in the .bashrc file of the user the git push command runs as on the server.