Information: Finding the GCLID in your Apache server logs
In the process of setting up Autotagging, I found I was unable to locate the GCLID parameter in the HTTP_REFERER. As such, I believed the GCLID was not being passed to my website.
I was wrong.
After an absurd amount of time on the phone with the incredibly helpful Adwords team, I found that Apache, for whatever reason, drops the GCLID parameter from the HTTP_REFERER field when it logs the data. This, of course, seemed to me to be a problem at Google, not at my server.
Upon very careful inspection (on the 10th attempt) I discovered the GCLID parameter IS reaching the logs, just not in the HTTP_REFERER field. It is available in the QUERY_STRING field and the REQUEST_URI field.
Examples are below:
Re: Information: Finding the GCLID in your Apache server logs
This is true. the gclid is only found in the query string. I'm surprised folks on the AdWords team couldn't tell you that on the first call.
The referrer data is not reliable for identifying AdWords traffic. Look for the presence of the gclid value in the query string instead.
Best of Luck!