Checking if process still running?

Question

Hello,

As a way to build a poor-man's watchdog and make sure an application is restarted in case it crashes (until I figure out why), I need to write a PHP CLI script that will be run by cron every 5mn to check whether the process is still running.

Based on this page, I tried the following code, but it always returns True even if I call it with bogus data:

function processExists($file = false) {
    $exists= false;
    $file= $file ? $file : __FILE__;

    // Check if file is in process list
    exec("ps -C $file -o pid=", $pids);
    if (count($pids) > 1) {
    $exists = true;
    }
    return $exists;
}

#if(processExists("lighttpd"))
if(processExists("dummy"))
    print("Exists\n")
else
    print("Doesn't exist\n");

Next, I tried this code...

(exec("ps -A | grep -i 'lighttpd -D' | grep -v grep", $output);)
print $output;

... but don't get what I expect:

/tmp> ./mycron.phpcli 
Arrayroot:/tmp> 

FWIW, this script is run with the CLI version of PHP 5.2.5, and the OS is uClinux 2.6.19.3.

Thank you for any hint.

---

Edit: This seems to work fine

exec("ps aux | grep -i 'lighttpd -D' | grep -v grep", $pids);
if(empty($pids)) {
        print "Lighttpd not running!\n";
} else {
        print "Lighttpd OK\n";
}

Answer 1

You can try this, which combines bits of those two approaches:

function processExists($processName) {
    $exists= false;
    exec("ps -A | grep -i $processName | grep -v grep", $pids);
    if (count($pids) > 0) {
        $exists = true;
    }
    return $exists;
}

If that doesn't work, you may want to just try running the ps command on your system and seeing what output it gives.

Answer 2

I'd use pgrep to do this (caution, untested code):

exec("pgrep lighttpd", $pids);
if(empty($pids)) {

    // lighttpd is not running!
}

I have a bash script that does something similar (but with SSH tunnels):

#!/bin/sh

MYSQL_TUNNEL="ssh -f -N -L 33060:127.0.0.1:3306 tunnel@db"
RSYNC_TUNNEL="ssh -f -N -L 8730:127.0.0.1:873 tunnel@db"

# MYSQL
if [ -z `pgrep -f -x "$MYSQL_TUNNEL"` ] 
then
    echo Creating tunnel for MySQL.
    $MYSQL_TUNNEL
fi

# RSYNC
if [ -z `pgrep -f -x "$RSYNC_TUNNEL"` ]
then
    echo Creating tunnel for rsync.
    $RSYNC_TUNNEL
fi

You could alter this script with the commands that you want to monitor.

Answer 3

i have a function to get the pid of a process...

function getRunningPid($processName) {
    $pid = 0;
    $processes = array();
    $command = 'ps ax | grep '.$processName;
    exec($command, $processes);
    foreach ($processes as $processString) {
        $processArr = explode(' ', trim($processString));
            if (
            (intval($processArr[0]) != getmypid())&&
            (strpos($processString, 'grep '.$processName) === false)
        ) {
            $pid = intval($processArr[0]);
        }
    }
    return $pid;
}

Answer 4

If you're doing it in php, why not use php code:

In the running program:

define('PIDFILE', '/var/run/myfile.pid');

file_put_contents(PIDFILE, posix_getpid());
function removePidFile() {
    unlink(PIDFILE);
}
register_shutdown_function('removePidFile');   

Then, in the watchdog program, all you need to do is:

function isProcessRunning($pidFile = '/var/run/myfile.pid') {
    if (!file_exists($pidFile) || !is_file($pidFile)) return false;
    $pid = file_get_contents($pidFile);
    return posix_kill($pid, 0);
}

Basically, posix_kill has a special signal 0 that doesn't actually send a signal to the process, but it does check to see if a signal can be sent (the process is actually running).

And yes, I do use this quite often when I need long running (or at least watchable) php processes. Typically I write init scripts to start the PHP program, and then have a cron watchdog to check hourly to see if it's running (and if not restart it)...