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Archive for March 17th, 2008

Hang on Fedora boot: Problem of starting sendmail service

Posted by icecafe on March 17, 2008

I. Problem description: 

when i changed the network setting for the ethernet. I figured that it hangs out at starting sendmail.

This is realted to domainname and hostname. While checking for sendmail service, if the system have unresolvable hostname and domainname it hangs up there.

I was having hostname: localhost, and domainname: localdomain. But i changed to my choice. so the system hangs up due to my unresovable host and domain name.

Once you face this problem, boot in the interactive mode, and give yes for all option other than “starting sendmail”. then go to network settings. Make sure you change the hostname to “localhost”, and domainname to “localdomain”. Also make sure the ip address and dns are correct. This setting is for home user.

If you are in a specific domain say “xyz.net”, then get the hostname from the admin and change this setting. Then save it and reboot in the regular way. that shd work. This is the right solution for that reason.
II. Solutions:

To disable sendmail from loading on startup you can do the following as root user.

1. Verify it’s running (Run level 5 is the one you really care about if you do graphical login)

$ chkconfig –list sendmail

2. Disable it

$ chkconfig sendmail off

3. Verify it’s turned off

$ chkconfig –list sendmail

OR:

Follow this to disable sendmail:

1.Get to the bootloader screen where you come to the Fedora Core 6 screen where you hit Enter and proceed and Linux starts booting up.

2.Select the menu and hit “a”.

3.Now hit spacebar and type “single” and hit “Enter”

4.Linux will boot up into and eventually give you something like bash#

5.Type chkconfig sendmail off and hit enter

6.Hit Ctrl + D till Linux reboots

< From Internet: http://www.linuxquestions.org/questions/fedora-35/fedora-core-6-halts-after-installation-and-restart-510248/&gt;

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Managing Services in Fedora

Posted by icecafe on March 17, 2008

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.

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

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