Java™ Application Development on Linux - Dator

456Chapter 20Open Source Web <strong>Application</strong> Serversstatus_at() {status /usr/sbin/atd}case "$1" instart)start;;stop)stop;;reload|restart)restart;;condrestart)if [ -f /var/lock/subsys/atd ]; thenrestartfi;;status)status_at;;*)echo $"Usage: $0 {start|stop|restart|condrestart|status}"exit 1esacexit $?exit $RETVALThis script is from a RedHat Linux system. Those comments at the topare a magic incantation for the chkconfig program that ships with that distribution11 (and with Fedora Core). We’ll talk more about chkconfig in the nextsection.As you can see, the basic premise is that when a daemon is started, theprocess ID is saved into a file. If the “stop” option is passed, the PID is lookedup and the process is killed. That’s the basic idea. But wait! There’s more!Each runlevel has a directory of scripts. Let’s look at the contents of sucha directory (Example 20.3).11. The RedHat chkconfig program is conceptually similar to the one in the IRIX operatingsystem.