The Application Server

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<?php
$sock = socket_create(AF_INET, SOCK_DGRAM, SOL_UDP);
socket_bind($sock, '0.0.0.0', 10000);

for (;;) {
    socket_recvfrom($sock, $message, 1024, 0, $ip, $port);
	echo "received: " . $message;
    $reply = str_rot13($message);
    socket_sendto($sock, $reply, strlen($reply), 0, $ip, $port);
}

Let’s start it:

php server.php

And test it in another terminal:

$ nc -u 127.0.0.1 10000
Hello, world!
Uryyb, jbeyq!

Turning Application Server into a Service

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create service file named rot13.service

sudo vim /lib/systemd/system/rot13.service
or
sudo vim /etc/systemd/system/rot13.service

add the following contents

[Unit]
Description=ROT13 demo service
After=network.target
StartLimitIntervalSec=0

[Service]
Type=simple
Restart=always
RestartSec=1
User=username
ExecStart=/usr/bin/env php /path/to/server.php
ExecStop=/path/to/stop/script

[Install]
WantedBy=multi-user.target

• User - username that runs the application
• ExecStart - path to start script
• ExecStop - path to stop script

load systemd service

sudo systemctl daemon-reload

now you can run the systemd commands:

systemctl enable rot13
systemctl disable rot13
systemctl start rot13
systemctl stop rot13
systemctl restart rot13
systemctl status rot13

Going further

• https://www.freedesktop.org/software/systemd/man/systemd.service.html

  List indent undo

  • Systemd - Creating .service Files - Going Further