Controlling Services With chkconfig
Many system 5 UNIX variants use scripts in the /etc/rcN.d/ directories to control which services should be started in the various runlevels. If, for instance, you wanted the secure shell daemon to run in runlevel 4, you would put a script named something like “S55sshd” in “/etc/rc4.d”. This script would usually accept the “start” “stop” and “restart” arguments, as well as the commands to perform these functions. When the system came up, it would execute “/etc/rc4.d/S55sshd start” when it transitioned into runlevel 4. On the way down, it would execute “/etc/rc4.d/S55sshd stop” as the system passed from runlevel 4 to runlevel 3. If you had made some changes to the sshd configuration file, and wanted to restart the service, you could manually execute “/etc/rc3.d/sshd restart” to kill and then restart the daemon.
Since this model involved having multiple copies of the same script in many different directories, Linux and others have adopted the standard of putting all service control scripts in “/etc/init.d/”, and using symbolic links to these scripts in the various “/etc/rcN.d/” directories. This allowed for the SGI IRIX innovation of the “chkconfig” command, which is command line tool that manages the symbolic links for you.
How to use “chkconfig” in Red Hat Enterprise Linux:
First, all your service control scripts need to be in the “/etc/init.d/” directory. They should reflect the name of the service they control. In our example, the file is named /etc/init.d/sshd”.
Secondly, they have a tag at the head of the script that looks something like this so that “chkconfig” understands that it can controll it:
# Basic support for IRIX style chkconfig
###
# chkconfig: 2345 55 25
# description: Manages the services you are controlling with the chkconfig command
###
The first set of numbers “2345″ is are the default runlevels for the service, and “55″ and “25″ represent the name of the “S” and “K” symbolic links, and the order in which the service will be started and stopped in the respective runlevel. You will need to change these last two numbers, making them unique.
Once these requirements are met, using the command is fairly simple. When we go into /etc/rc3.d, we see a file called “S55sshd”.
[root@calvin rc2.d]# cd /etc/rc3.d
[root@calvin rc2.d]# ls -al S55sshd
lrwxrwxrwx 1 root root 14 Nov 15 15:10 S55sshd -> ../init.d/sshd
We see this file is a symbolic link to “../init.d/sshd”. Let’s run the “chkconfig” command to turn sshd off.
[root@calvin init.d]# /sbin/chkconfig sshd off
[root@calvin init.d]# /sbin/chkconfig –list sshd
sshd 0:off 1:off 2:off 3:off 4:off 5:off 6:off
chkconfig --list sshd confirms that sshd has been disabled in all runlevels, and the symbolic link has been removed from all “/etc/rcN.d/” directories.
Let’s turn sshd back on:
[root@calvin init.d]# /sbin/chkconfig sshd on
[root@calvin rc2.d]# /sbin/chkconfig –list sshd
sshd 0:off 1:off 2:on 3:on 4:on 5:on 6:off
chkconfig --list sshd confirms that sshd has now been enabled in runlevels 2, 3, 4 and 5, and we see s symbolic link to “/etc/init.d/sshd” named “S55sshd” in “/etc/rc2.d/”, “/etc/rc3.d/”, “/etc/rc4.d/” and “/etc/rc5.d/”.
Let’s imagine now that we only want sshd to be enabled in runlevel 5. We run the following command to accomplish this:
[root@calvin rc2.d]# /sbin/chkconfig sshd –level 234 off
cd /etc/[root@calvin rc2.d]# /sbin/chkconfig –list sshd
sshd 0:off 1:off 2:off 3:off 4:off 5:on 6:off
chkconfig --list sshd confirms that sshd has been disabled in all runlevels except 5, and the “S55sshd” has been removed from “/etc/rc2.d/”, “/etc/rc3.d/” and “/etc/rc4.d/”.
There is, of course, more to it, but this should get you well on your way to happily managing your system services with “chkconfig”.
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13 Responses to “Controlling Services With chkconfig”
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Nice article Cliff.
Any insight on what the numbers on this line are for?
#chkconfig: 235 19 08
Sure… Good question.
The “chkconfig: 235″ section indicates the the default runlevels. For instance, if we ran “chkconfig sshd on”, it would be active in runlevels 2,3 and 5.
The “19″ and “08″ numbers indicate the order of startup and kill. This means that using this tag, the startup symbolic link would be named “S19sshd” and the symbolic link to kill the process would be named “K08sshd”.
Update:
I have changed “#chkconfig: 235 19 08″ in the story to “#chkconfig: 2345 55 25″ so that it works with the rest of the examples.
“#chkconfig: 235 19 08″ actually came from the VmWare script, but it was nicely crafted, making it easy to understand what it is doing.
I’ve also included a quick explanation of what these numbers mean.
Yeah, “chkconfig” is a nice management tool. Run level 4 is unused, so your example might confuse some n00bs (lol h4×0r!)
[...] That should pretty much do it. If you don’t have autofs configured to start up, you can use chkconfig to enable it. “/misc/backups” will now be mounted whenever a user or process attempts to access data on it, and it will be automatically disconnected after 120 seconds of inactivity. Last, but not least, you can always confirm that it is running with the “service” command: [...]
[...] Remember to use “chkconfig” to make sure “ntpd” is enabled to come up when the system starts. [...]
Thanks for the nice explanation of how-to do it.
what is the difference between run level 3 and run level 4 in linux.
Well, by default, runlevel 4 is unused. If you were to enter runlevel 4 on a new system, it would look exactly the same as runlevel 5. It is there, however, so you can controll custom items with it in case you find yourself needing a middle ground between runlevel 3 and 5. 3, of course is full multiuser mode without X, while 5 is full multiuser mode with X. You would use runlevel 4 if you still wanted X running, but not everything normally running in 5.
[...] asterisk service with chkconfig and service.) [...]
[...] script is chkconfig compatible, so call it the name of your new service and put it in [...]
[...] script is chkconfig compatible, so call it the name of your new service and put it in [...]
I’m starting openoffice as startup service according the follow url
http://little.bluethings.net/2008/05/30/automating-document-conversion-in-linux-using-jodconverterooo/
[root@suse ~]# sudo service openoffice start
openoffice: unrecognized service
What is this error?