I'm trying to use the -c option of twistd like this : twistd web --wsgi bar.app -c foo.cer -k privkey.pem --https=4433 I'm pointing it at a cert with perms like this "-rw-r--r-- 1 root root" but twistd complains about a permission error . I'm puzzled ... surely twistd only needs to read that file ? Thanks .