Upgrade Path from 2.1.0

I'm working with a client who has a custom application which was written using CodeIgniter v 2.1.0 and they want to upgrade the CodeIgniter environment as well as the PHP version that the application is sitting on (5.6.37) and the MySQL MariaDB (10.2.17).

Can I do a jump straight to 3.1.9 or do I need to go to 3.0.x first (doing all of the associated activities mentioned in the Release Notes) and then consider further upgrading the technical environment?

Any suggestions/hints/things to look out for when dealing with a system which has been neglected for this amount of time?

Thanks for any and all assistance.

Use the Upgrade guides. You also need to update other dependencies, if you are using a library.
https://www.codeigniter.com/userguide3/i...ading.html

1. BACKUP
2. BACKUP AGAIN!
3. Replace system folder from 2.0 to 3.1.9
4. Follow all steps from 2.1.0 to 3.1.9
5. Run application

Personally I upgraded from 2.x into 2.2.3 first, but it depends on the size of the application.

Use the Upgrade guides. You also need to update other dependencies, if you are using a library.
https://www.codeigniter.com/userguide3/i...ading.html

1. BACKUP
2. BACKUP AGAIN!
3. Replace system folder from 2.0 to 3.1.9
4. Follow all steps from 2.1.0 to 3.1.9
5. Run application

Personally I upgraded from 2.x into 2.2.3 first, but it depends on the size of the application.

Thank you for the response, I totally agree about backups. I wondered if slow and steady was the better idea. It's a fairly large application (a custom CRM system) so I have some concerns regarding changes related to depreciated coding structures and changes to naming conventions. I'm trying to work out the best way to attack this so it is done in a controlled fashion, doesn't take until the ants take over the earth and doesn't drive me crazy ;-)

You can jump straight to 3.1.9, BUT you will need to go through each version's Release Notes and do each of the "Steps".

Obviously, make a complete backup before starting!

The first upgrade guide is the most important and has the largest set of steps. Pay particular attention to the Step 1 in those instructions. You can ignore Step 1 in all the subsequent upgrade guides because you have already installed the most recent "system" directory.

You will also want to use the following files from version 3.1.9 right from the start
index.php
config/mimes.php
config/constants.php

If the session library is using the database driver then do Step 2 of this guide when you get to Step 6 of Upgrading from 2.2.x to 3.0.x.

You are probably going to have to go through all the changes before even trying to run the upgraded site.

It has been a while since I've done an upgrade from v2 but I have done a few. It's not really that hard. Just be sure you understand each and every "Step".

In my mind Step 10 of Upgrading from 2.2.x to 3.0.x was the one that resulted in the most code rewriting.

You can jump straight to 3.1.9, BUT you will need to go through each version's Release Notes and do each of the "Steps".

Obviously, make a complete backup before starting!

The first upgrade guide is the most important and has the largest set of steps. Pay particular attention to the Step 1 in those instructions. You can ignore Step 1 in all the subsequent upgrade guides because you have already installed the most recent "system" directory.

You will also want to use the following files from version 3.1.9 right from the start
index.php
config/mimes.php
config/constants.php

If the session library is using the database driver then do Step 2 of this guide when you get to Step 6 of Upgrading from 2.2.x to 3.0.x.

You are probably going to have to go through all the changes before even trying to run the upgraded site.

It has been a while since I've done an upgrade from v2 but I have done a few. It's not really that hard. Just be sure you understand each and every "Step".

In my mind Step 10 of Upgrading from 2.2.x to 3.0.x was the one that resulted in the most code rewriting.

Thank you for taking the time to reply and provide so much clear information. 

I thought that I may have to do this fairly slowly to ensure it works correctly, but at least at the end of it we'll have something beautiful and shiny and up to date and I shouldn't have to do many updates for a while 

...but at least at the end of it we'll have something beautiful and shiny and up to date and I shouldn't have to do many updates for a while 

Not until they want to upgrade to version 4 anyway.