Migrating from Joomla 1.5 to Joomla 2.5

Introduction
1. Transferring content
2. Transferring extensions:
  2.1. jDownloads and jComments
  2.2. Template, editor, and other extensions
Epilogue

Upd: Русская версия статьи: Миграция с Joomla 1.5 на Joomla 2.5. Предисловие.

It took 4.5 months from the time of writing an article, where I tried to talk about choosing a version of CMS Joomla! and reasonability of transfer from old versions to new ones. During this time, Joomla 1.5 has ceased to please me completely, especially since the sites running this version started make problems - in particular, one of them had been hacked twice. 3.0 has been continuing to expand, third party developers has been actively creating extensions for it, but I still stopped at 2.5, which had time to study and appreciate very positively. The site, which you are reading now, moved from 1.5.22 to 2.5.8 at the beginning of December 2012, and at the end of February 2013 I upgraded it to 2.5.9. Another site, the one that hacked when it was at 1.5, had been transfered directly to 2.5.9 in mid-February. At both - normal flight.

The migration process I will attempt to describe in detail was formed as a result of processing large amounts of information from the web, as well as a number of attempts to reduce it to a minimum of manual work. For example, at the first step of the migration - use the jUpgrade utility - I was trying to transfer extensions along the core content, but because of their total incompatibility with the new version, the new site became messed up, and its performance was close to zero. So I decided to move only content at first, then to install extensions separately and on each to determine, how to easily and quickly restore its customary settings and data.

So please keep in mind that it will be enough of handwork. The described scenario does not provide for the transfer of a dozen sites by pressing a couple of buttons, and, I am afraid, such way does not exist at present time. But it is guaranteed to lead to the obtaining of fully functioning site running 2.5 while preserving of the content and most settings from your old site of 1.5.

A small disclaimer:

All that I am describing I have myself successfully done not once. However, if inattentively follow the instructions, you can corrupt all that is possible. So before you start - backup files and databases! Also, I would advise you to save intermediate results, ensure that a failure does not have to roll back to the beginning of the process. I've done everything on my local web server, thoroughly tested and only then uploaded to hosting. I am recommending to go the same way.