Can you tell me differences between the following sysvinit /sbin/service command:
service httpd restart
service httpd condrestart
service httpd reload
init is a program for Linux an Unix-based systems to spawns all other processes. It runs as a daemon and has PID 1. The boot loader starts the kernel and the kernel starts init. A Linux or Unix based system can be started up into various runlevels. The /etc/init.d/ directory stores various shell scripts which can be used for:
- Load kernel drivers ( modules ).
- Check and mount file systems.
- Setup network.
- Mount remote file systems (such as nfs).
- Start web server and other services.
You can use the following syntax to control various services:
# /etc/init.d/NAME start|stop|restart|status|reload|condrestart
OR
# /sbin/services NAME start|stop|restart|status|reload|condrestart
Where,
- start : Start a service (such as Apache by typing ‘service httpd start’)
- stop : Stop a service (such as Apache by typing ‘service httpd stop’).
- restart : Restart (stop and then start) a service (such as Apache by typing ‘service httpd restart’) .
- status : Find out whether a service is currently running or not (such as Apache by typing ‘service httpd status’) .
- reload : Reloads the config file without interrupting pending operations(reload Apache web server after the config file changes using ‘service httpd reload’) .
- condrestart : Restarts if the service is already running (such as Apache by typing ‘service httpd condrestart).
Service command is used to run a System V init script. Usually all system V init scripts are stored in /etc/init.d directory and service command can be used to start, stop, and restart the daemons and other services under Linux.
Sample Session With service Command
Open a terminal and type the following commands:
Where,
- Start a httpd server.
- Restart a httpd server.
- Stop a httpd server.
- Find a status of httpd server.
- Start a httpd server.
- Find a status of httpd server.
- Edit /etc/httpd/conf/httpd.conf file and reload the server.
- Restarts if the httpd service is already running.
- See Apache error log file.
Sample SysVInit Script
The service script can define arbitrary commands. In this example ‘service httpd graceful’ provides additional options to httpd server:
#!/bin/bash # # httpd Startup script for the Apache HTTP Server # # chkconfig: - 85 15 # description: The Apache HTTP Server is an efficient and extensible \ # server implementing the current HTTP standards. # processname: httpd # config: /etc/httpd/conf/httpd.conf # config: /etc/sysconfig/httpd # pidfile: /var/run/httpd/httpd.pid # ### BEGIN INIT INFO # Provides: httpd # Required-Start: $local_fs $remote_fs $network $named # Required-Stop: $local_fs $remote_fs $network # Should-Start: distcache # Short-Description: start and stop Apache HTTP Server # Description: The Apache HTTP Server is an extensible server # implementing the current HTTP standards. ### END INIT INFO # Source function library. . /etc/rc.d/init.d/functions if [ -f /etc/sysconfig/httpd ]; then . /etc/sysconfig/httpd fi # Start httpd in the C locale by default. HTTPD_LANG=${HTTPD_LANG-"C"} # This will prevent initlog from swallowing up a pass-phrase prompt if # mod_ssl needs a pass-phrase from the user. INITLOG_ARGS="" # Set HTTPD=/usr/sbin/httpd.worker in /etc/sysconfig/httpd to use a server # with the thread-based "worker" MPM; BE WARNED that some modules may not # work correctly with a thread-based MPM; notably PHP will refuse to start. # Path to the apachectl script, server binary, and short-form for messages. apachectl=/usr/sbin/apachectl httpd=${HTTPD-/usr/sbin/httpd} prog=httpd pidfile=${PIDFILE-/var/run/httpd/httpd.pid} lockfile=${LOCKFILE-/var/lock/subsys/httpd} RETVAL=0 STOP_TIMEOUT=${STOP_TIMEOUT-10} # The semantics of these two functions differ from the way apachectl does # things -- attempting to start while running is a failure, and shutdown # when not running is also a failure. So we just do it the way init scripts # are expected to behave here. start() { echo -n $"Starting $prog: " LANG=$HTTPD_LANG daemon --pidfile=${pidfile} $httpd $OPTIONS RETVAL=$? echo [ $RETVAL = 0 ] && touch ${lockfile} return $RETVAL } # When stopping httpd, a delay (of default 10 second) is required # before SIGKILLing the httpd parent; this gives enough time for the # httpd parent to SIGKILL any errant children. stop() { echo -n $"Stopping $prog: " killproc -p ${pidfile} -d ${STOP_TIMEOUT} $httpd RETVAL=$? echo [ $RETVAL = 0 ] && rm -f ${lockfile} ${pidfile} } reload() { echo -n $"Reloading $prog: " if ! LANG=$HTTPD_LANG $httpd $OPTIONS -t >&/dev/null; then RETVAL=6 echo $"not reloading due to configuration syntax error" failure $"not reloading $httpd due to configuration syntax error" else # Force LSB behaviour from killproc LSB=1 killproc -p ${pidfile} $httpd -HUP RETVAL=$? if [ $RETVAL -eq 7 ]; then failure $"httpd shutdown" fi fi echo } # See how we were called. case "$1" in start) start ;; stop) stop ;; status) status -p ${pidfile} $httpd RETVAL=$? ;; restart) stop start ;; condrestart|try-restart) if status -p ${pidfile} $httpd >&/dev/null; then stop start fi ;; force-reload|reload) reload ;; graceful|help|configtest|fullstatus) $apachectl $@ RETVAL=$? ;; *) echo $"Usage: $prog {start|stop|restart|condrestart|try-restart|force-reload|reload|status|fullstatus|graceful|help|configtest}" RETVAL=2 esac exit $RETVAL |