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Services and Daemons

indexterm:[services configuration] Maintaining security on your system is extremely important, and one approach for this task is to manage access to system services carefully. Your system may need to provide open access to particular services (for example, `httpd` if you are running a web server). However, if you do not need to provide a service, you should turn it off to minimize your exposure to possible bug exploits.

This chapter covers the configuration of the services to be run when a system is started, and provides information on how to start, stop, and restart the services on the command line using the systemctl utility.

Keep the system secure

When you allow access for new services, always remember that both the firewall and SELinux need to be configured as well. One of the most common mistakes committed when configuring a new service is neglecting to implement the necessary firewall configuration and SELinux policies to allow access for it. For more information, refer to the 29 Security Guide.

Configuring Services

To allow you to configure which services are started at boot time, Fedora is shipped with the systemctl command line tool.

Do not use the ntsysv and chkconfig utilities

Although it is still possible to use the ntsysv and chkconfig utilities to manage services that have init scripts installed in the /etc/rc.d/init.d/ directory, it is advised that you use the systemctl utility.

Enabling the irqbalance service

To ensure optimal performance on POWER architecture, it is recommended that the irqbalance service is enabled. In most cases, this service is installed and configured to run during the 29 installation. To verify that irqbalance is running, type the following at a shell prompt:

systemctl status irqbalance.service

Enabling the Service

To configure a service to be automatically started at boot time, use the systemctl command in the following form:

systemctl enable service_name.service

The service will be started the next time you boot the system. For information on how to start the service immediately, refer to Running the Service.

Příklad 1. Enabling the httpd service

Imagine you want to run the Apache HTTP Server on your system. Provided that you have the httpd package installed, you can enable the httpd service by typing the following at a shell prompt as root:

~]# systemctl enable httpd.service

Disabling the Service

To disable starting a service at boot time, use the systemctl command in the following form:

systemctl disable service_name.service

The next time you boot the system, the service will not be started. For information on how to stop the service immediately, refer to Stopping the Service.

Příklad 2. Disabling the telnet service

In order to secure the system, users are advised to disable insecure connection protocols such as Telnet. You can make sure that the telnet service is disabled by running the following command as root:

~]# systemctl disable telnet.service

Running Services

The systemctl utility also allows you to determine the status of a particular service, as well as to start, stop, or restart a service.

Do not use the service utility

Although it is still possible to use the service utility to manage services that have init scripts installed in the /etc/rc.d/init.d/ directory, it is advised that you use the systemctl utility.

Checking the Service Status

To determine the status of a particular service, use the systemctl command in the following form:

systemctl status service_name.service

This command provides detailed information on the service’s status. However, if you merely need to verify that a service is running, you can use the systemctl command in the following form instead:

systemctl is-active service_name.service

Příklad 3. Checking the status of the httpd service

Enabling the httpd service illustrated how to enable starting the httpd service at boot time. Imagine that the system has been restarted and you need to verify that the service is really running. You can do so by typing the following at a shell prompt:

~]$ systemctl is-active httpd.service
active

You can also display detailed information about the service by running the following command:

~]$ systemctl status httpd.service
httpd.service - LSB: start and stop Apache HTTP Server
          Loaded: loaded (/etc/rc.d/init.d/httpd)
          Active: active (running) since Mon, 23 May 2011 21:38:57 +0200; 27s ago
         Process: 2997 ExecStart=/etc/rc.d/init.d/httpd start (code=exited, status=0/SUCCESS)
        Main PID: 3002 (httpd)
          CGroup: name=systemd:/system/httpd.service
                  ├ 3002 /usr/sbin/httpd
                  ├ 3004 /usr/sbin/httpd
                  ├ 3005 /usr/sbin/httpd
                  ├ 3006 /usr/sbin/httpd
                  ├ 3007 /usr/sbin/httpd
                  ├ 3008 /usr/sbin/httpd
                  ├ 3009 /usr/sbin/httpd
                  ├ 3010 /usr/sbin/httpd
                  └ 3011 /usr/sbin/httpd

To display a list of all active system services, use the following command:

systemctl list-units --type=service

This command provides a tabular output with each line consisting of the following columns:

UNIT — A systemd unit name. In this case, a service name.
LOAD — Information whether the systemd unit was properly loaded.
ACTIVE — A high-level unit activation state.
SUB — A low-level unit activation state.
JOB — A pending job for the unit.
DESCRIPTION — A brief description of the unit.

Příklad 4. Listing all active services

You can list all active services by using the following command:

~]$ systemctl list-units --type=service
UNIT                      LOAD   ACTIVE SUB     JOB DESCRIPTION
abrt-ccpp.service         loaded active exited      LSB: Installs coredump handler which saves segfault data
abrt-oops.service         loaded active running     LSB: Watches system log for oops messages, creates ABRT dump directories for each oops
abrtd.service             loaded active running     ABRT Automated Bug Reporting Tool
accounts-daemon.service   loaded active running     Accounts Service
atd.service               loaded active running     Job spooling tools
[output truncated]

In the example above, the abrtd service is loaded, active, and running, and it does not have any pending jobs.

Running the Service

To run a service, use the systemctl command in the following form:

systemctl start service_name.service

This will start the service in the current session. To configure the service to be started at boot time, refer to Enabling the Service.

Příklad 5. Running the httpd service

Enabling the httpd service illustrated how to run the httpd service at boot time. You can start the service immediately by typing the following at a shell prompt as root:

~]# systemctl start httpd.service

Stopping the Service

To stop a service, use the systemctl command in the following form:

systemctl stop service_name.service

This will stop the service in the current session. To disable starting the service at boot time, refer to Enabling the Service.

Příklad 6. Stopping the telnet service

Disabling the telnet service illustrated how to disable starting the telnet service at boot time. You can stop the service immediately by running the following command as root:

~]# systemctl stop telnet.service

Restarting the Service

To restart a service, use the systemctl command in the following form:

systemctl restart service_name.service

Příklad 7. Restarting the sshd service

For any changes in the /etc/ssh/sshd_config configuration file to take effect, it is required that you restart the sshd service. You can do so by typing the following at a shell prompt as root:

~]# systemctl restart sshd.service

Additional Resources

Installed Documentation

systemctl(1) — The manual page for the systemctl utility.

Related Books

29 Security Guide: A guide to securing Fedora. It contains valuable information on how to set up the firewall, as well as the configuration of SELinux.

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