The standard start/stop scripts are located in /etc/init.d or for older linux versions /etc/rc.d/init.d.
Stop proftpd: /etc/init.d/proftpd stop
Start proftpd: /etc/init.d/proftpd start
If you run cPanel there is a restart script located at /scripts/restartsrv.
To restart proftpd run /scripts/restartsrv proftpd
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