php-pcntlHow to create a daemon using PCNTL fork in PHP?

Creating a daemon using PCNTL fork in PHP is a simple process. The following example code will create a daemon that will run in the background and output a message every 5 seconds:

<?php

declare(ticks = 1);

pcntl_signal(SIGCHLD, SIG_IGN);

$pid = pcntl_fork();

if ($pid == -1) {
    die('could not fork');
} else if ($pid) {
    // parent process
    exit();
} else {
    // child process
    while (true) {
        echo "I'm a daemon\n";
        sleep(5);
    }
}

Output example

I'm a daemon
I'm a daemon
I'm a daemon
...

The code consists of the following parts:

1. declare(ticks = 1): This sets the number of ticks that PHP will wait before running signal handlers.

2. pcntl_signal(SIGCHLD, SIG_IGN): This tells PHP to ignore the SIGCHLD signal, which is sent when a child process terminates.

3. pcntl_fork(): This creates a child process.

4. if ($pid == -1): This checks if the fork failed.

5. else if ($pid): This is the parent process.

6. else: This is the child process.

7. while (true): This creates an infinite loop.

8. echo "I'm a daemon\n": This outputs a message.

9. sleep(5): This pauses the loop for 5 seconds.

Helpful links

• PHP: pcntl_fork - Manual
• PHP: pcntl_signal - Manual

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