PHP Process ID and unique

php

Solution

From php.net/getmypid

with little modification to disable non cli access.

script can be executed using `/usr/bin/php script.php`.

Additionally use `nohup /usr/bin/php script.php > nohup.out &` to launch a nohup process in background.

#!/usr/bin/php 
<?php 

if ( PHP_SAPI !== 'cli' ) {
    die( "Cmd line access only!\n" );
}

define( 'LOCK_FILE', "/var/run/".basename( $argv[0], ".php" ).".lock" );  // can also use /tmp
if( isLocked() ) die( "Already running.\n" ); 

# The rest of your script goes here.... 
echo "Hello world!\n"; 
sleep(30); 

unlink( LOCK_FILE ); 
exit(0); 

function isLocked() 
{ 
    # If lock file exists, check if stale.  If exists and is not stale, return TRUE 
    # Else, create lock file and return FALSE. 

    if( file_exists( LOCK_FILE ) ) 
    { 
        # check if it's stale 
        $lockingPID = trim( file_get_contents( LOCK_FILE ) ); 

       # Get all active PIDs. 
        $pids = explode( "\n", trim( `ps -e | awk '{print $1}'` ) ); 

        # If PID is still active, return true 
        if( in_array( $lockingPID, $pids ) )  return true; 

        # Lock-file is stale, so kill it.  Then move on to re-creating it. 
        echo "Removing stale lock file.\n"; 
        unlink( LOCK_FILE ); 
    } 

    file_put_contents( LOCK_FILE, getmypid() . "\n" ); 
    return false; 

} 
?>

Problem

I want to run a php script on background and store its PID on database. So that I can check if the particular script running or not (later). We can use `getmypid` to get current PID. But as per the PHP manual Process IDs are not unique, thus they are a weak entropy source. We recommend against relying on pids in security-dependent contexts. ...and I cannot rely on PID. My second idea is to store the process created time to the database. How can I get the current script created time? And later how can I compare with tasklist to check whether the particular script is running or not? I am running on a shared host, windows/linux environment.

Original source