Checking if process still running?

Question

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

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)...