Create run.sh script and systemd service

 run.service

New file
@@ -0,0 +1,13 @@
[Unit]
Description=TTSS update service
After=network.target

[Service]
Type=simple
Restart=always
RestartSec=1
User=www-data
ExecStart=/usr/bin/php /path/to/run.sh

[Install]
WantedBy=multi-user.target

 run.sh

New file
@@ -0,0 +1,16 @@
#!/bin/sh

DIRNAME=$(dirname "$0")
cd "${DIRNAME}"

(
flock -n 200 || exit 1

while true
do
    php download.php
    sleep 4
done

) 200>./lock