For those of you who run a local server using MAMP or MAMP Pro to develop WordPress themes or plugins, or just have a local version of your site to test before making any changes on a live environment (which I highly recommend), after installing OS X Yosemite, the application might throw an error stating that it failed to start Apache.
Thers is an easy fix for that. Just go to your Applications -> MAMP -> bin -> apache2 -> bin folder, find envvars file and rename it to _envvars.
You can now start MAMP and there should be no issues starting Apache.
Why should you run a local web server if you are not a developer? You just don't wanna mess with your live site by testing out new themes, styles or plugins. The installation of a local server is simple and you can have a clone of your site locally so you can make sure that any changes you make will not have a negative impact on your website. Don't know how to do it and need a tutorial for this? Just let me know in the comments section below and I'll prepare one for you.