`nginx -t` creates the file /run/nginx.pid if it doesn't exist. `nginx -t` is
executed by ExecStartPre (in nginx.service) and creates /run/nginx.pid with the
correct SELinux context. However, when manually running `nginx -t` from the
cmdline, the SELinux transition for systemd services doesn't occur and
/run/nginx.pid is created with the wrong SELinux context. A workaround is to
make sure that the PID file is removed before starting nginx.
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