I want to downgrade laravel to version 4.0 as i'm facing lots of issue with the current version. There is no guide on the internet. What is the procedure to downgrade laravel in ubuntu?
It depends.
If you started with a L4.0 installation, upgraded it to L4.1, you should be able to git cherry-pick your commits to undo the update.
If you started with L4.1 then you should carefully examine the differences between https://github.com/laravel/laravel/tree/v4.1.18 and https://github.com/laravel/laravel/tree/v4.0.9
Watch all the files that changed in the upgrade guide and download the older files from github.
Don't forget to update your composer.json to have this in the required object:
"laravel/framework": "4.0.*",
Then run composer update --no-scripts.