I had issues with processes locking up. This script checks for processes and kills them if they are older than a certain time.
Its uses some functions you'll need to define or remove, like slog() which I use for logging, and is_running() which checks if this script is already running so you can add it to cron without running multiple copies.
Hope this helps someone 
Jack.
#!/usr/bin/php
<?
if (is_running()) die();
slog("monitor started",2);
while(true){
check_process("convert"); // kill convert processes over 5 minutes old (default)
check_process("bash",1440); // kill bash processes over 1440 minutes old
check_process("qmail-smtpd",30); // kill qmail-smtpd processes over 30 minutes old
sleep(300);
}
function cmd($cmd){
$fp = popen($cmd, 'r');
$ret="";
while ($read = fread($fp, 2096)) $ret = $ret.$read;
pclose($fp);
return $ret;
}
function kill_pid($pid){
slog("kill_pid: killing [$pid]",2);
posix_kill($pid,1);
}
function check_process($cmd,$max_runtime=5) {
$now = getdate();
$h = $now['hours'];
$m = $now['minutes'];
$nowtime = ($h*3600)+($m*60);
$x = cmd("ps h -fC $cmd");
if ($x){
$x = explode("\n",$x);
foreach($x as $l){
if ($l){
while (strstr($l," ")) $l = str_replace(" "," ",$l);
list($owner,$pid,$ppid,$c,$stime,$tty,$s,$time,$cmd) = explode(" ",$l);
if (!strstr($stime,":")) {
slog("check_process: $cmd : STIME [$stime] - more than a day old",2);
kill_pid($pid);
} else {
slog("check_process: $cmd : check runtime");
list($sh,$sm) = explode(":",$stime);
$runtime = ($sh*3600)+($sm*60);
$diff = ($nowtime - $runtime)/60;
if ($diff>$max_runtime){
slog("check_process: $cmd : STIME [$stime] now [$h:$m] - over $max_runtime minutes since start",2);
kill_pid($pid);
} else slog("check_process: $cmd : STIME [$stime] now [$h:$m] - running $diff/$max_runtime minutes",2);
}
}
}
} else slog("check_process: $cmd : no processes",2);
}
?>