On a SharePoint 2013 farm we recently had search throw errors consistently being unable to crawl and index content. Looking into the crawl logs, I saw the error “The filtering process has been terminated”. Doing a quick search on Bing led me to this post for SharePoint 2010. It is in German, but if you translate it the gist of it is to make sure the service account has full control to the Temp directory. So I went in to all of my search servers and granted full control on the c:temp directory to wss_wpg as well as wss_admin_wpg. I think only the former group is necessary, however, and full control is probably a bit much. Write permission should be sufficient.
After making that change and restarting the search services on all servers, I was able to get the farm to perform a successful crawl.
I don’t normally post content that others already cover, but I thought this was worthy since I didn’t see anyone else run into this with 2013. I also thought it important to point out the requirement to restart the services, as I found some forum posts that didn’t state that need.