Managing Services in Fedora

Mauriat Miranda (http://www.mjmwired.net/contact/)

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Published: 28 February 2006 (updated: 28 February 2006)

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Introduction

This guide is to show how to control services in Fedora Core linux. Explanations included are services, runlevels, setting services, and controlling services.

Service

A service (often called a daemon) is a specific application that runs in the background and is usually non-interactive. They can be used for anything, including hardware, network access, monitoring, logging, etc. All operating systems use some set of services to automate actions.

Runlevel

A runlevel is a mode of operation that is used to group certain sets of daemons based on some purpose or restricted use. For the Fedora/Redhat based Linux systems, the primary runlevels in Fedora are:

• runlevel 1: Single-User Mode
• runlevel 2: Multi-User Mode
• runlevel 3: Multi-User Mode with Networking
• runlevel 5: X11 (runlevel 3 + X Window System "the GUI").

Typically most users run with the X-server in runlevel 5, and many servers without X-servers run in runlevel 3. Usually runlevel 1 has no services running.

To determine what runlevel you are using, run:

# /sbin/runlevel

To determing what runlevel your system will start at the next boot, run:

# cat /etc/inittab | grep :initdefault: id:5:initdefault:

Similarily you can edit the file /etc/inittab and change the initdefault value at line ~18.

To switch runlevels, you can run the following, replace RUNLEVEL with the appropriate number (3, 5, etc.):

# /sbin/init RUNLEVEL

Note: When switching FROM runlevel 5 to another runlevel, you might accidentally kill your X-server and entire GUI. Always make sure you are at a text console (CTRL-ALT-F1,F2,F3,F4) before switching runlevels.

To force a runlevel at boot without modifying /etc/inittab, you pass a number to end of the kernel from the Grub menu. At boot, higlight the option you wish to boot and before hitting <Enter>, hit <E>. Go to the end of the kernel line and add a 3 or 5. Then hit <Enter> and boot (<B> to boot).

Enable/Disabling Services

Every service must be set to either be "On" (enabled) or "Off" (disabled) for every runlevel.

To see what services are enabled for each runlevel, run:

# /sbin/chkconfig --list

To control which services are enabled for a runlevel, run system-config-services in the GUI or ntsysv at the command line. (Previous Fedora releases may have serviceconf instead of system-config-services).

To manually enable a specific service use chkconfig. The following command turns crond daemon for both runlevel 3 *AND* 5.

# /sbin/chkconfig --level 35 crond on

The --level could be 1, 2, 3, 4, 5 or any combination of the numbers. The on option can also be off. Running man chkconfig is useful.

Controlling Services

Regardless of how a service is enabled a runlevel or if it is defaulted to "On" or "Off", every service can be started or stopped and managed at runtime.

To see what services you have running run:

# /sbin/service --status-all

To individually control a single service, use service. For example:

# /sbin/service crond status crond (pid 1604) is running...

The status option can be replace with start, stop, status, reload, restart and sometimes other options also. For example:

[root@charon ~]# service crond Usage: /etc/init.d/crond {start|stop|status|reload|restart|condrestart} [root@charon ~]# service crond stop Stopping crond: [ OK ] [root@charon ~]# service crond start Starting crond: [ OK ] [root@charon ~]# service crond restart Stopping crond: [ OK ] Starting crond: [ OK ]

All services located in the directory: /etc/init.d/ can be controlled this way. An alternate form of control would be:

# /etc/init.d/crond status

Virtually all of the above functionality. Is available through the GUI, using system-config-services. However there are times when problems with the GUI (X-server) may prevent you from controlling your services. Hence understanding the commands are very helpful.

reference:

http://www.mjmwired.net/resources/mjm-fedora-manage-services.html