It doesn't appear to be possible to run more than one local web server for a given project. This is annoying as it means shutting down one web server and firing up another when running acceptance tests. For example I'd like to be able to run the following and have it just work:

APP_ENV=dev symfony server:start  --port 1234 --no-tls --quiet &
APP_ENV=test symfony server:start  --port 1235 --no-tls --quiet &

Right now one of the servers starts and the other one either exits with an unhelpful error "Unable to start PHP-FPM" or just silently exits.