freepbx-tftp-server/configs/freepbx-tftp-server.service

[Unit]
Description=FreePBX tftp server
After=network.target

[Service]
Type=simple
Restart=on-failure
RestartSec=10

WorkingDirectory=/opt/freepbx-tftp-server
ExecStart=/opt/freepbx-tftp-server/freepbx-tftp-server -workdir=/tftpboot

[Install]
WantedBy=multi-user.target