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Redhat Linux Runlevels

Redhat Linux Runlevels

By Tom Connelly

The order in which Linux starts system services is governed by what runlevel is assigned to the service in question. Some runlevels will boot or halt the system itself, while others control regular system services or even programs that the administrator installs and wants started at a particular time in the boot cycle. These runlevels are controlled with scripts that are defined by runlevel named directories in which they reside. The default runlevel for the system is set in the /etc/inittab file, but it can be overridden from the GRUB boot loader menu. Redhat Enterprise Linux has six runlevels.

Runlevel 0: Halt the system. When the system is sent to this runlevel, everything shuts down and the system is completely halted. If the computer’s BIOS supports it, the machine is powered off at the end of the process.

Runlevel 1: This is single user mode. In single user mode an administrator can do all sorts of maintenance, like backups, restores, and repairs. This is useful because no other users can be logged in and the system is not prone to having others change things, which is important when this sort of work is being done. Networking is not enabled so the network interfaces and infrastructure are offline.

Runlevel 2: In this runlevel, multiuser functionality is enabled with only some networking services enabled.

Runlevel 3: Multiuser mode is enabled with full networking functionality.

Runlevel 4: This runlevel is currently not used.

Runlevel 5: The X Windows graphical user interface system is enabled and the user is brought to a graphical login screen. After logging in, the user is taken to their graphical desktop as in all of the popular operating systems of today. Networking is fully enabled.

Runlevel 6: This is the reboot runlevel. It does what it says and reboots the system. You should never set the /etc/inittab default runlevel to number 6 for obvious reasons. Your system would be in an endless reboot loop.

Each runlevel has a bunch of scripts associated with it. Runlevel 3 scripts are located in the /etc/rc.d/rc3.d directory. The runlevel directories are rc0.d through rc6.d, and they are all located under the /etc/rc.d directory. Whatever the default runlevel is set to in the /etc/inittab file, the system will look in the appropriate runlevel directory and execute the scripts in numeric order, starting and killing services according to the scripts. The start scripts start with an “S” and the kill scripts with a “K”. The scripts in the runlevel directories are really just symbolic links to the real script files in the /etc/rc.d/init.d directory. The /etc/rc.d/ rc(number).d directory is hard linked to /etc/rc(number).d directory, so you can use the shorter one to get to the same place.

Knowing about Linux runlevels is an important part about knowing how to handle a Linux system, and the knowledge translates to UNIX systems as well. There will be minor and subtle differences, such as varying directory names and different boot loaders, but it is essentially the same framework.

Tom has worked for technology companies for 15+ years starting as a software quality assurance tech and migrating over to IT as a UNIX, Linux, and Windows systems operator and administrator. The Techbait technology and tech products portal is the place to be for geeks on the go. http://techbait.net

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Linux Training and Red Hat Certification

By John Kol Marsh

In today’s competitive IT world, knowledge of Linux can help shape the future of a person. Apart from knowledge in languages such as Java, C++,.net, PHP, knowledge of Linux can help in securing a very good career. Linux was created by Linus Torvalds. The source code of Linux which is called the Kernel is available for free on the internet. Anyone can download and develop it in a unique way. Many companies have already released their own versions of Linux. This makes it a very unique operating system. Every version of Linux is different from the other in one way or the other.

Linux is one of the preferred operating systems for corporate houses.

· One of the greatest advantages of using it is because it’s swift in multitasking. It is very stable in terms of crashing and rebooting. Many other operating systems have to be rebooted from time to time to run efficiently.

· As it is a free-operating system, the bugs are fixed within a very short span of time. If a bug is reported, many people will offer solution to the problem like a community based approach.

· It is secured operating system because of the fact that it is virus-free. This is because it does not recognize or run the virus or worms.

This makes it a perfect operating system for corporate and databases.

Linux training can help in gaining sufficient knowledge about Linux. It is different from the most popular operating system like Microsoft Windows. There are many variations in Linux and one of the most popular versions is Red Hat Linux.

In order that a person needs to fully understand and operate a Linux based system, he or she needs to have required knowledge and training. Red Hat Certification or RHCE Certification is the certificate which is given to those expert users who get through the Red Hat Training and Examinations. Red Hat Training includes Red Hat Essentials, System Administration, Security & Networking Administration, Red Hat Enterprise Linux Virtualization.

Now the question of which professional institute to choose arises. There are plenty of institutes that provide Red Hat Linux. But, one of the best Corporate Linux Training provider is Zonix Systems. Zonix systems has scaled up to the position of a leading Linux Corporate Training providers within a short span of time. The reasons are the course curriculum that they follow and the Team Members. The Team members include some of the best names in the Information Technology industry.

Zonix Systems has teamed up with Red Hat to provide training and Red Hat Certifications. Zonix Systems also provides case study analysis which is a very practical approach in learning the subject.

Zonix Systems is not just a training institute, but it is also provides Linux Support/ Consulting Services and Linux Based Mail Server as well. These Linux Support/ Consulting Services and Linux Based Mail Server services are much needed by Corporate Companies which need advice on implementing and enhancing their operating systems. This Linux training center is located in Noida, and Delhi, India.
Buy the Red Hat Linux Certification Study Guide today!

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Are You Getting Sick Of Microsoft Windows? It’s Time To Give Ubuntu Linux A Whirl
By Alan Oliver

About 18 months ago, I had another disastrous crash on my PC that caused me to lose a host of photos, music and documents. Luckily I had a backup of most of my documents on an external disk. So I wasn’t too concerned by this. I had experienced many crashes on Windows before and usually I was able to recover most of my documents and restore the system back to normal without too much effort.

This time was different however and to my horror, I discovered that Windows had somehow corrupted my external disk as well. I had lost everything and was pretty angry about it.

I tried a number of data recovery programs but most of the files wore gone. Forever. What a disaster! At that point I decided that I would look for another alternative to windows and I thought I would give Linux another try.

RedHatA few years earlier I had experimented with RedHat Linux but had no real success with it as it had problems detecting my usb keyboard and mouse. Which was obviously a bit of a non-starter for me. I knew that big advances were being made in the Linux world so I decided to do a bit of research.

Linux is an operating system that is free. That is, it can be downloaded and copied and distributed without a fee. It is free in a deeper sense too. Most of the software is written under a license called the “GPL” which effectively means that source code is available to everyone for each and every component of the Linux Operating System. If you have access to the source code for a piece of software then you can change the program to fix bugs and make it better. Once you do this you are under obligation to make your new source code available to others.
This has worked extremely well and Linux is being developed by programmers all over the world to make it better and better. The progress is amazing!

In my research I discovered a website: distrowatch.com. This website keeps a list of the most popular distributions of Linux. A distribution is a collection of Linux software that together makes an operating system. Each distribution contains different software and has a different focus. There are so many to try… Fedora, Mandrake, Puppy, PCLinuxOS, Debian, Knoppix, and the most popular, Ubuntu Linux.

ubuntu128x130I downloaded the ISO of Ubuntu Linux from the Ubuntu website http://www.ubuntu.com/ and burned it to cd (an ISO file is cd image that can be recreated using a cd burning tool such as Nero). I placed the cd in my drive and booted up my computer.

I was astounded!

Within 10 minutes my computer was running Ubuntu Linux without even having to install it! This was a “Live-CD” and it can be used without installing to hard disk – it can be run from a cd without affecting your computer at all.

All my hardware was detected and within minutes I was surfing the web using Firefox and getting my email using Evolution, chatting to friends in messenger and yahoo chat using Gaim, writing documents and opening spreadsheets in Open Office and listening to Internet Radio with RythmBox.

I was delighted with the easy to use and gorgeous looking desktop. I decided to install it straight away and since then I haven’t looked back.

There is an abundance of free open source software just waiting for you to experience. The package management system – Synaptic, allows you to search repositories of software and download them. The quality of a lot of the software is incredible.

Linux is written from the ground up to be a secure operating system. This means that you won’t have to worry about getting viruses, spyware or any other kind of malware. My system is as stable as a rock.
Of course, there are downsides to running Linux. The main one is that there is a learning curve that can be quite steep. It is not windows so If you are trying to get something working, your windows knowledge will not help you.
You might need to troubleshoot problems using the Command Line Interface – similar to windows DOS, but many times more powerful.

Fortunately, help is at hand on the incredibly friendly and helpful forums at ubuntuforums.org
I have been running Ubuntu Linux now for 18 months and can’t see any reason now to return to windows. Once you get past the mind set of using closed source software a whole new world opens up before you and you realise that amazing things are possible with linux.

I hope you found this article helpful and I hope it inspires you to try out Ubuntu Linux as I did. You won’t regret trying it.

Here are some resources:

distrowatch.com

Distrowatch – News on the latest Linux distributions.

ubuntu.com

Ubuntu – Download the Ubuntu Linux operating system for your computer

ubuntuforums.com

Ubuntu Forums – Go here for help and advice

wikipedia.org/wiki/Linux

Linux on Wikipedia

order linux on cd from frogshape!

http://www.frogshape.com

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