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Service Scripts: /etc/init.d

Most server software using RPM Red Hat packages will automatically install the startup scripts and create the needed links in the appropriate

rc

N

.d directories, where N is the runlevel number. Startup scripts, though, can be used for any program you may want run when your system starts up. To have such a program start automatically, you first create a startup script for it in the

/etc/rc.d/init.d directory, and then create symbolic links to that script in the

/etc/rc.d/rc3.d and

/etc/rc.d/rc5.d directories. A shutdown link (K) should also be placed in the

rc6.d directory used for runlevel 6 (reboot).

Service Script Functions

A simplified version of the startup script

httpd uses on Red Hat systems is shown in a later section. You can see the different options, listed in the

/etc/rc.d/init.d/httpd example, under the

case statement:

start ,

stop ,

status ,

restart , and

reload . If no option is provided (

* ),the script use syntax is displayed. The

httpd script first executes a script to define functions used in these startup scripts. The

daemon function with

httpd actually executes the

/usr/sbin/httpd server program.

echo -n "Starting httpd: "
daemon httpd
echo
touch /var/lock/subsys/httpd

The

killproc function shuts down the daemon. The lock file and the process ID file (

httpd.pid ) are then deleted:

 killproc httpd
echo
rm -f /var/lock/subsys/httpd
rm -f /var/run/httpd.pid

The

daemon ,

killproc , and

status functions are shell scripts defined in the

function s script, also located in the

inet.d directory. The

functions script is executed at the beginning of each startup script to activate these functions. A list of these functions is provided in Table 20-4.

. /etc/rc.d/init.d/functions

Service Script Tags

The beginning of the startup script holds tags used to configure the server. These tags, which begin with an initial

# symbol, are used to provide runtime information about the service to your system. The tags are listed in Table 20-5, along with the startup functions. You enter a tag with a preceding

# symbol, the tag name with a colon, and then the tag arguments. For example, the

processname tag specifies the name of the program being executed, in this example

httpd :

# processname: httpd

If your script starts more than one daemon, you should have a

processname entry for each. For example, the Samba service starts up both the

smdb and

nmdb daemons.

# processname: nmdb

The end of the tag section is indicated by an empty line. After this line, any lines beginning with a

# are treated as comments. The

chkconfig line lists the default runlevels that the service should start up on, along with the start and stop priorities. The following entry lists runlevels 3, 4, and 5 with a start priority of 85 and a stop of 15:

# chkconfig: 345 85 15

For the description, you enter a short explanation of the service, using the \ symbol before a newline to use more than one line.

# description: Apache Web server

With

config tags, you specify the configuration files the server may use. In the case of the Apache Web server, there may be three configuration files:

# config: /etc/httpd/conf/access.conf
# config: /etc/httpd/conf/httpd.conf
# config: /etc/httpd/conf/srm.conf

The

pidfile entry indicates the file where the server's process ID is held.

Service Script Example

As an example, a simplified version of the Web server startup script,

/etc.rc.d/init.d/httpd

, is shown here. Most scripts are much more complicated, particularly when determining any arguments or variables a server may need to specify when it starts up. This script has the same name as the Web server daemon,

httpd :

#!/bin/sh
#
# Startup script for the Apache Web Server
#
# chkconfig: 35 85 15
# description: Apache is a World Wide Web server. # It is 
used to serve HTML files and CGI.
# processname: httpd
# pidfile: /var/run/httpd.pid
# config: /etc/httpd/conf/access.conf
# config: /etc/httpd/conf/httpd.conf
# config: /etc/httpd/conf/srm.conf
# Source function library.
. /etc/rc.d/init.d/functions
# See how we were called.
case "$1" in
start)
echo -n "Starting httpd: "
daemon httpd
echo
touch /var/lock/subsys/httpd
;;
stop)
killproc httpd
echo
rm -f /var/lock/subsys/httpd
rm -f /var/run/httpd.pid
;;
status)
status httpd
;;
restart)
$0 stop
$0 start
;;
reload)
echo -n "Reloading httpd: "
killproc httpd -HUP
echo
;;
*)
echo "Usage: $0 {start|stop|restart}"
exit 1
esac
exit 0

Installing Service Scripts

The RPM packaged versions for an Internet server include the startup script for that server. Installing the RPM package installs the script in the

/etc/rc.d/init.d directory and creates its appropriate links in the runlevel directories, such as

/etc/rc.h/rc3.d . If you decide, instead, to create the server using its source code files, you can then manually install the startup script. If no startup script exists, you first make a copy of the

httpd script— renaming it—and then edit the copy to replace all references to

httpd with the name of the server daemon program. Then place the copy of the script in the

/etc/rc.d/init.d directory and make a symbolic link to it in the

/etc/rc.d/rc3.d directory. Or you could use redhat-config-services to create the link in the

/etc/rc.d/rc3.d directory. Select File | Refresh Services. When you start your system now, the new server is automatically started up, running concurrently and waiting for requests.