So how do you disable these services so that they are not started at boot time?
The answer to that depends on the type of Linux distribution you are using. True, many Linux distributions including Ubuntu bundle with them a GUI front end to accomplish the task which makes it easier to enable and disable the system services. But there is no standard GUI utility common across all Linux distributions. And this makes it worth while to learn how to enable and disable the services via the command line.
But one thing is common for all Linux distributions which is that all the start-up scripts are stored in the '/etc/init.d/' directory. So if you want to say, enable apache webserver in different run levels, then you should have a script related to the apache webserver in the /etc/init.d/ directory. It is usually created at the time of installing the software. And in my machine (which runs Ubuntu), it is named apache2. Where as in Red Hat, it is named httpd. Usually, the script will have the same name as the process or daemon.
Here I will explain different ways of enabling and disabling the system services.
1) Red Hat Method
Red Hat and Red Hat based Linux distributions make use of the script called chkconfig to enable and disable the system services running in Linux.
For example, to enable the apache webserver to start in certain run levels, you use the chkconfig script to enable it in the desired run levels as follows:
# chkconfig httpd --add# chkconfig httpd on --level 2,3,5This will enable the apache webserver to automatically start in the run levels 2, 3 and 5. You can check this by running the command:
# chkconfig --list httpdOne can also disable the service by using the off flag as shown below:
# chkconfig httpd off# chkconfig httpd --delRed Hat also has a useful script called service which can be used to start or stop any service. Taking the previous example, to start apache webserver, you execute the command:
# service httpd startand to stop the service...
# service httpd stopThe options being start, stop and restart which are self explanatory.
2) Debian Method
Debian Linux has its own script to enable and disable services across runlevels. It is called update-rc.d. Going by the above example, you can enable apache webserver as follows:
# update-rc.d apache2 defaults... this will enable the apache webserver to start in the default run levels of 2,3,4 and 5. Of course, you can do it explicitly by giving the run levels instead of the "defaults" keyword as follows:
# update-rc.d apache2 start 20 2 3 4 5 . stop 80 0 1 6 .The above command modifies the sym-links in the respective /etc/rcX.d directories to start or stop the service in the destined runlevels. Here X stands for a value of 0 to 6 depending on the runlevel. One thing to note here is the dot (.) which is used to terminate the set which is important. Also 20 and 80 are the sequence codes which decides in what order of precedence the scripts in the /etc/init.d/ directory should be started or stopped.
And to disable the service in all the run levels, you execute the command:
# update-rc.d -f apache2 removeHere -f option which stands for force is mandatory.
But if you want to enable the service only in runlevel 5, you do this instead:
# update-rc.d apache2 start 20 5 . stop 80 0 1 2 3 4 6 .3) Gentoo Method
Gentoo also uses a script to enable or disable services during boot-up. The name of the script is rc-update . Gentoo has three default runlevels. Them being: boot, default and nonetwork. Suppose I want to add the apache webserver to start in the default runlevel, then I run the command:
# rc-update add apache2 default... and to remove the webserver, it is as simple as :
# rc-update del apache2To see all the running applications at your runlevel and their status, similar to what is achieved by chkconfig --list, you use the rc-status command.
# rc-status --all4) The old fashioned way
I remember the first time I started using Linux, there were no such scripts to aid the user in enabling or disabling the services during start-up. You did it the old fashioned way which was creating or deleting symbolic links in the respective /etc/rcX.d/ directories. Here X in rcX.d is a number which stands for the runlevel. There can be two kinds of symbolic links in the /etc/rcX.d/ directories. One starts with the character 'S' followed by a number between 0 and 99 to denote the priority, followed by the name of the service you want to enable. The second kind of symlink has a name which starts with a 'K' followed by a number and then the name of the service you want to disable. So in any runlevel, at any given time, for each service, there should be only one symlink of the 'S' or 'K' variety but not both.
So taking the above example, suppose I want to enable apache webserver in the runlevel 5 but want to disable it in all other runlevels, I do the following:
First to enable the service for run level 5, I move into /etc/rc5.d/ directory and create a symlink to the apache service script residing in the /etc/init.d/ directory as follows:
# cd /etc/rc5.d/# ln -s /etc/init.d/apache2 S20apache2This creates a symbolic link in the /etc/rc5.d/ directory which the system interprets as - start (S) the apache service before all the services which have a priority number greater than 20.
If you do a long listing of the directory /etc/rc5.d in your system, you can find a lot of symlinks similar to the one below.
lrwxrwxrwx 1 root root 17 Mar 31 13:02 S20apache2 -> ../init.d/apache2Now if I start a service, I will want to stop the service while rebooting or while moving to single user mode and so on. So in those run levels I have to create the symlinks starting with character 'K'. So going back to the apache2 service example, if I want to automatically stop the service when the system goes into runlevel 0, 1 or 6, I will have to create the symlinks as follows in the /etc/rc0.d, /etc/rc1.d/, /etc/rc6.d/ directories.
# ln -s /etc/init.d/apache2 K80apache2One interesting aspect here is the priority. Lower the number, the higher is the priority. So since the starting priority of apache2 is 20 - that is apache starts way ahead of other services during startup, we give it a stopping priority of 80. There is no hard and fast rule for this but usually, you follow the formula as follows:
If you have 'N' as the priority number for starting a service, you use the number (100-N) for the stopping priority number and vice versa.
Basic premise:
/etc/inittab is a configuration file which describes which processes are started at bootup
The important config for startup programs launched is the run level: # The default runlevel is defined here
id:3:initdefault:.d/
Here Runlevel 3 is configured.
This means that services which Runlevel 3 is defined will be launched on startup.
All services that are enabled to run at startup for this level can be found in /etc/init.d/rc3.d Similarly, for other levels: rc0.d:
S20halt
rc1.d:
K02single K09splash K10fbset K21coldplug S01coldplug S12fbset S13kbd S13splash S20single
rc2.d:
K02gpm K07cups K10rpmconfigcheck K14splash_early K16syslog S01stqdaemon S07snmpd S09hprsm S13splash S17ivr
K04plweb K08hwscan K10running-kernel K15fazzt K17network S05network S07weblogic S12fbset S14hwscan S17splash_late
K05ivr K08xntpd K13cmanic K15informix K21coldplug S06syslog S08hpasm S12raw S14xntpd S18plweb
K05splash_late K09splash K13hprsm K15mms K21random S07fazzt S08resmgr S12rpmconfigcheck S15cups S20gpm
K06atd K10fbset K14hpasm K15snmpd S01coldplug S07informix S08splash_early S12running-kernel S16atd
K06cron K10raw K14resmgr K15weblogic S01random S07mms S09cmanic S13kbd S16cron
rc3.d:
K02gpm K06smb K09xinetd K12nfsboot K15informix S01random S08hpasm S12autofs S13splash S16cron
K04plweb K06squid K10autofs K13cmanic K15mms S01stqdaemon S08portmap S12fbset S13xinetd S16dhcpd
K05ivr K07cups K10fbset K13hprsm K15nmb S05network S08resmgr S12named S14hwscan S16hpsmhd
K05smbfs K07postfix K10named K13hpvca K15snmpd S06syslog S08splash_early S12orbacus S14nfsserver S16smb
K05splash_late K07rsyncd K10orbacus K13nfslock K15weblogic S07fazzt S09cmanic S12raw S14xntpd S16squid
K06atd K08hwscan K10raw K14hpasm K16syslog S07informix S09hprsm S12rpmconfigcheck S15cups S17ivr
K06autoyast K08nfsserver K10rpmconfigcheck K14portmap K17network S07mms S09hpvca S12running-kernel S15postfix S17smbfs
K06cron K08xntpd K10running-kernel K14resmgr K21coldplug S07nmb S09nfslock S12sshd S15rsyncd S17splash_late
K06dhcpd K09ct_intel K10sshd K14splash_early K21random S07snmpd S10nfs S13ct_intel S16atd S18plweb
K06hpsmhd K09splash K12nfs K15fazzt S01coldplug S07weblogic S10nfsboot S13kbd S16autoyast S20gpm
rc4.d:
K06hpsmhd K13cmanic K13hprsm K13hpvca K14hpasm S08hpasm S09cmanic S09hprsm S09hpvca S16hpsmhd
rc5.d:
K04plweb K06squid K09xinetd K12nfsboot K15informix S01random S08hpasm S12autofs S13splash S16autoyast
K05ivr K07cups K10autofs K13cmanic K15mms S01stqdaemon S08portmap S12fbset S13xinetd S16cron
K05smbfs K07postfix K10fbset K13hprsm K15nmb S05network S08resmgr S12named S14hwscan S16dhcpd
K05splash_late K07rsyncd K10named K13hpvca K15snmpd S06syslog S08splash_early S12orbacus S14nfsserver S16hpsmhd
K06atd K07xdm K10orbacus K13nfslock K15weblogic S07fazzt S09cmanic S12raw S14xntpd S16smb
K06autoyast K08hwscan K10raw K14hpasm K16syslog S07informix S09hprsm S12rpmconfigcheck S15cups S16squid
K06cron K08nfsserver K10rpmconfigcheck K14portmap K17network S07mms S09hpvca S12running-kernel S15postfix S17ivr
K06dhcpd K08xntpd K10running-kernel K14resmgr K21coldplug S07nmb S09nfslock S12sshd S15rsyncd S17smbfs
K06hpsmhd K09ct_intel K10sshd K14splash_early K21random S07snmpd S10nfs S13ct_intel S15xdm S17splash_late
K06smb K09splash K12nfs K15fazzt S01coldplug S07weblogic S10nfsboot S13kbd S16atd S18plweb
rc6.d:
S20reboot
rcS.d:
S10boot.clock S13kbd S13splash S20single
All files that start with the letter K are kill services (they call the service script with stop as an argument)
All files that start with the letter S are start services (they call the service script with start as an argument)
All Kill scripts are run first then all the Start scripts.
Both the Kill and Start scripts are run in numerical order (ie. S01... is run before S02...)
In the Runlevel 3 directory /etc/init.d/rc3.d you'll notice that all the services listed are symbolic links to a script in the /etc/init.d dir: lrwxrwxrwx 1 root root 11 2006-11-09 10:48 S07weblogic -> ../weblogic
lrwxrwxrwx 1 root root 8 2006-11-09 10:48 S07snmpd -> ../snmpd
lrwxrwxrwx 1 root root 6 2006-11-09 10:48 S07nmb -> ../nmb
lrwxrwxrwx 1 root root 6 2006-11-09 10:48 S07mms -> ../mms
lrwxrwxrwx 1 root root 11 2006-11-09 10:48 S07informix -> ../informix
lrwxrwxrwx 1 root root 8 2006-11-09 10:48 S07fazzt -> ../fazzt
Let's take a closer look at one of these services scheduled to launch on startup S07weblogic -> ../weblogic
The chkconfig command allows you to manage services for startup.
To check the configuration of a service script found in /etc/init.d run the following command: chkconfig --list weblogic
weblogic 0:off 1:off 2:on 3:on 4:off 5:on 6:off
This means the weblogic service is enabled for Runlevel 2,3, and 5 (ie. found in rc2.d, rc3.d and rc5.d directories
The weblogic script starts weblogic up at boot time when the system starts up under the above runlevels
The script looks like the following: #!/bin/sh
#
# weblogic start and shutdown
#
# Copyright (c) Shoppers Drug Mart 2005
#
# Bootup and shutdown script
#
# /etc/init.d/weblogic
#
### BEGIN INIT INFO
# Provides: weblogic
# Required-Start: $network $nfs $informix
# Required-Stop:
# Default-Start: 2 3 5
# Default-Stop:
# Description: Start weblogic server
### END INIT INFO
trap "exit 255" 1 2 3 # ignore signals
ADMIN_HOME=/apps/appserver/prod/asAdmin
case $1 in
'start')
echo "Starting weblogic..."
#
# have the system run out of /appserver/prod/asAdmin/
#
# start weblogic as asuser
#
su asuser -c "cd ${ADMIN_HOME}/utils; ./startServer.ksh ALL >${ADMIN_HOME}/logs/boot.log 2>&1" &
;;
'stop')
echo "Stopping weblogic..."
su asuser -c "cd ${ADMIN_HOME}/utils; ./stopServer.ksh ALL >${ADMIN_HOME}/logs/stop.log 2>&1"
;;
*)
echo "Usage: $0 {start|stop}"
;;
esac
anything you put in /etc/rc.d starting with rc. is run at startup. The file has to be executable also. Here is the content of script that was installed by default in my /etc/rc.d/rc.httpd
#!/bin/sh
#
# /etc/rc.d/rc.httpd
#
# Start/stop/restart the Apache web server.
#
# To make Apache start automatically at boot, make this
# file executable: chmod 755 /etc/rc.d/rc.httpd
#
case "$1" in
'start')
/usr/sbin/apachectl start ;;
'stop')
/usr/sbin/apachectl stop ;;
'restart')
/usr/sbin/apachectl restart ;;
*)
echo "usage $0 start|stop|restart" ;;
esac
As you can see, it is very alike but with a little more options. (restart is very useful).
NAME
chkconfig - updates and queries runlevel information for system services
SYNOPSIS
chkconfig --list [name]
chkconfig --add name
chkconfig --del name
chkconfig [--level levels] name
chkconfig [--level levels] name
DESCRIPTION
chkconfig provides a simple command-line tool for maintaining the /etc/rc[0-6].d directory hierarchy by relieving system administrators of the task of directly manipulating the numerous symbolic links in those directories.
This implementation of chkconfig was inspired by the chkconfig command present in the IRIX operating system. Rather than maintaining configuration information outside of the /etc/rc[0-6].d hierarchy, however, this version directly manages the symlinks in /etc/rc[0-6].d. This leaves all of the configuration information regarding what services init starts in a single location.
chkconfig has five distinct functions: adding new services for management, removing services from management, listing the current startup information for services, changing the startup information for services, and checking the startup state of a particular service.
When chkconfig is run without any options, it displays usage information. If only a service name is given, it checks to see if the service is configured to be started in the current runlevel. If it is, chkconfig returns true; otherwise it returns false. The --level option may be used to have chkconfig query an alternative runlevel rather than the current one.
If one of on, off, or reset is specified after the service name, chkconfig changes the startup information for the specified service. The on and off flags cause the service to be started or stopped, respectively, in the runlevels being changed. The reset flag resets the startup information for the service to whatever is specified in the init script in question.
By default, the on and off options affect only runlevels 2, 3, 4, and 5, while reset affects all of the runlevels. The --level option may be used to specify which runlevels are affected.
Note that for every service, each runlevel has either a start script or a stop script. When switching runlevels, init will not re-start an already-started service, and will not re-stop a service that is not running.
OPTIONS
--level levels
Specifies the run levels an operation should pertain to. It is given as a string of numbers from 0 to 7. For example, --level 35 specifies runlevels 3 and 5.
--add name
This option adds a new service for management by chkconfig. When a new service is added, chkconfig ensures that the service has either a start or a kill entry in every runlevel. If any runlevel is missing such an entry, chkconfig creates the appropriate entry as specified by the default values in the init script. Note that default entries in LSB-delimited 'INIT INFO' sections take precedence over the default runlevels in the initscript.
--del name
The service is removed from chkconfig management, and any symbolic links in /etc/rc[0-6].d which pertain to it are removed.
--list name
This option lists all of the services which chkconfig knows about, and whether they are stopped or started in each runlevel. If name is specified, information in only display about service name.
RUNLEVEL FILES
Each service which should be manageable by chkconfig needs two or more commented lines added to its init.d script. The first line tells chkconfig what runlevels the service should be started in by default, as well as the start and stop priority levels. If the service should not, by default, be started in any runlevels, a - should be used in place of the runlevels list. The second line contains a description for the service, and may be extended across multiple lines with backslash continuation.
For example, random.init has these three lines:
# chkconfig: 2345 20 80
# description: Saves and restores system entropy pool for \
# higher quality random number generation.
This says that the random script should be started in levels 2, 3, 4, and 5, that its start priority should be 20, and that its stop priority should be 80. You should be able to figure out what the description says; the \ causes the line to be continued. The extra space in front of the line is ignored.
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