PHP Class for running a script as daemon in Linux. The script is started in the background by itself, to stop the daemon use filename.xphp --stop.

Daemon.php

<?php

/**
 * Class for running a script as daemon in Linux. The script is started
 * in the background by itself, to stop the daemon use filename.xphp --stop.
 *
 * $d = new Library_Cmd_Daemon('daemon.pid');
 * $d->run(function() {
 *   while(1) {
 *       sleep(10);
 *   }
 * });
 *
 */
class Library_Cmd_Daemon
{
    /**
     * File path for the pid file-
     *
     * @var string
     */
    private $pid_file;

    /**
     * The Process ID.
     *
     * @var int
     */
    private $pid;

    /**
     * Flag to indicate if the process is in daemon mode
     */
    private $daemon_mode = false;

    /**
     * Constructor
     *
     * @return void
     */
    function __construct($pid_file)
    {
        $this->pid_file = $pid_file;
    }

    /**
     * Destructor
     *
     * @return void
     */
    function __destruct()
    {
        if ($this->daemon_mode) {
            $this->clearPID();
        }
    }

    /**
     * Method for running the background code.
     *
     * @param Closure $func The code to be run.
     *
     * @return void
     */
    function run($func)
    {
        $bgdaemon = $stop = false;
        foreach ($_SERVER['argv'] as $e) {
            switch ($e) {
            case '--bgdaemon':
                $bgdaemon = true;
                break;
            case '--stop':
                $stop = true;
                break;
            case '--status':
                print $this->isRunning() ?
                    "The daemon is running\n" : "The daemon is not running.\n";
                return;
            case '--help':
                print "Available parameters are: --status and --stop.\n";
                return;
            }
        }

        // Check that the process is running
        if (!$this->isRunning()) {
            $this->clearPID();
        }

        // Kill the process
        if ($stop) {
            $this->stop();
            return;
        }

        // Background daemon stuff.
        if ($bgdaemon) {
            $this->daemon_mode = true;
            // Save the pid for later use.
            file_put_contents($this->pid_file, getmypid());

            $func();
            return;
        }

        $args = array();
        foreach ($_SERVER['argv'] as $k => $v) {
            // Don't include the filename.
            if ($k === 0) {
                continue;
            }

            $args[] = $v;
        }
        $args_c = implode(' ', $args);

        // daemonize
        if (!$this->isRunning()) {
            system("({$_SERVER["SCRIPT_NAME"]} $args_c --bgdaemon) >/dev/null &");
        }

    }

    /**
     * Detects if the process is running or not.
     *
     * @return bool
     */
    public function isRunning()
    {
        $pid = (int)@file_get_contents($this->pid_file);
        if ($pid === 0) {
            return false;
        }

        if (posix_getsid($pid) === false) {
            return false;
        }

        if (!file_exists("/proc/$pid/")) {
            return false;
        }

        $this->pid = $pid;
        return true;
    }

    /**
     * Clears all the PID information from the obj and the disk.
     *
     * @return void
     */
    private function clearPID()
    {
        @unlink($this->pid_file);
        $this->pid = 0;
    }

    /**
     * Method for stopping the running daemon.
     *
     * @return void
     */
    private function stop()
    {
        if ($this->pid === 0) {
            return;
        }

        posix_kill($this->pid, 9);
        $this->clearPID();
    }
}