All about Linux: Enabling and disabling services during start up in GNU/Linux
In any Linux distribution, some services are enabled to start at boot up by default. For example, on my machine, I have pcmcia, cron daemon, postfix mail transport agent … just to name a few, which start during boot up. Usually, it is prudent to disable all services that are not needed as they are potential security risks and also they unnecessarily waste hardware resources. For example, my machine does not have any pcmcia cards so I can safely disable it. Same is the case with postfix which is also not used.
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 2,3,5
This 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 httpd
One can also disable the service by using the off flag as shown below:
# chkconfig httpd off
# chkconfig httpd –del
Red 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 start
and to stop the service…
# service httpd stop
The options being start, stop and restart which are self explanatory.