Well, I need to make an LED lights through a button via PHP , use Fedora 22. Well, can do the programs in the Arduino IDE , and run them without problems , but when I access the port /dev/ttyACM0 with PHP he simply says he has no permission to access it , since I performed several operations via terminal, give permissions, and more. Could anyone help me step by step of how to do a simple communication with PHP and Arduino through the serial port ? Thank you all and forgive me for the mistakes I used the translator. 
You need to give the executing user of the php scripts permission to the serial devices.
I am not sure about fedora, with ubuntu however, you just add your php user (www-data) to the group dialout.