Can an script like: exec("/usr/local/bin/php /home/realrank/public_html/fork/do.php a abc> /dev/null &"); exec("/usr/local/bin/php /home/realrank/public_html/fork/do.php a abc> /dev/null &"); exec("/usr/local/bin/php /home/realrank/public_html/fork/do.php a abc> /dev/null &"); exec("/usr/local/bin/php /home/realrank/public_html/fork/do.php a abc> /dev/null &"); exec("/usr/local/bin/php /home/realrank/public_html/fork/do.php a abc> /dev/null &"); make the server to hang-up and become unavaible?!
It really depends on what do.php does. What I do to avoid potential problems is to avoid spawning threads within scripts. Anything "special" that I need to do in the background is done via a cron job. The job runs regularly (every 1 to 5 minutes) with a check at the beginning to ensure the script is not currently running.