How to use chkconfig command.

How To Use Chkconfig Command.

This guide will show you how to use the chkconfig command to control system services in Linux.

Modern Linux distributions come with the systemd initialization system that allows users to manage services with the systemctl command.

However, some older systems still use System V or Upstart. In that case, use the chkconfig command to list, start, and stop services, as well as enable or disable services from startup.

The chkconfig Command Syntax

The chkconfig command syntax looks like this:

chkconfig [options] [service] [subcommand]

The command works on its own but can also be used with:

• The –list, –level, –add, –del, and –override options specified before the service name. The options print the details or manage the service in question.

• The on, off, reset, or resetpriorities subcommands added after the service name. The subcommands change the startup info for the specified service.

The chkconfig Command Options.

However, executing the command with different options and subcommands enables users to manage services instead of only listing them. The table below shows the options and subcommands used with the chkconfig command:

The chkconfig Command Examples

The chkconfig command is the ultimate service managing tool for older Linux systems. The sections below outline common chkconfig examples.

List All Services

To list all services, execute the command without options or run:

chkconfig --list

Using –list with the chkconfig command displays the status of all available services in all runlevels. In case you want to sort services in alphabetical order, use the sort option:

chkconfig --list |sort

List All Enabled Services

To find all enabled services (in one or multiple runlevels), execute combine chkconfig –list with the grep command:

chkconfig --list | grep on

To find all disabled services (in one or multiple runlevels), run:

chkconfig --list | grep off

Furthermore, to narrow down the scope to the services on/off a particular runlevel, use:

chkconfig --list | grep --level <levels>:on

chkconfig --list | grep --level <levels>:off

For example, list all the services running in runlevel 5 with:

chkconfig --list | grep 5:on

On the other hand, to display all the services that are not running in runlevel 5, execute:

chkconfig --list | grep 5 :off

List a Particular Service

To show the startup configuration of a particular service in all runlevels, run chkconfig –list and specify the service.

chkconfig --list [service]

For example, check the status of the ntpd service in all runlevels with:

chkconfig --list ntpd

The output shows that the ntpd service is disabled on boot in any runlevel.

Enable a Service

Enable a service to start on boot with the chkconfig [service] on command. Next, confirm that the service is on using <strong>–list</strong>.

chkconfig [service] on
chkconfig --list [service]

The on option affects runlevels 2, 3, 4, and 5 and starts the ntpd service on boot on these runlevels. To enable a service on one or multiple runlevels only, run:

chkconfig  --level <levels> [service] on

For example, start the ntpd service on the third runlevel and verify the service’s configuration with:

chkconfig  --level 3 ntpd on
chkconfig --list ntpd

Similarly, to turn on the ntpd service in multiple runlevels in one go use:

chkconfig  --level 235 ntpd on
chkconfig --list ntpd

Disable a Service

Disable a service from starting at system boot with the chkconfig [service] off command:

chkconfig [service] off
chkconfig --list [service]

Even though the off variable also affects runlevels 2 to 5, users can specify in which runlevels to disable a service.

For instance, disable the ntpd service only in runlevel 3 and verify the results with:

chkconfig  --level 3 ntpd off
chkconfig --list ntpd

Add a Service 

Add a service to startup in all runlevels with the following command:

chkconfig --add [service]

For example, use the –add option to add ntpd to startup in all runlevels. Next, use –list to verify the service has been added:

chkconfig --add ntpd
chkconfig --list ntpd

The chkconfig command adds and configures the service as specified by the default values in the init script. For example, the ntpd service is disabled in every runlevel by default.

Remove a Service

Remove a service from startup in all runlevels with the –del option:

chkconfig --del [service]

The –del option removes the service from startup, but the service remains in the system. Therefore, to add the service back to startup, use the –add option again.

Reset Service Configuration

To reset the on/off status of a service in all runlevels as specified in the init script, execute:

chkconfig [service] reset

The output shows that ntpd returns to the default off status in all runlevels.

Conclusion

After reading this tutorial, you know how to use the chkconfig command to manage services in older versions of Linux.