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Types and dialects of Linux

Linux Tips by Burleson Consulting

What is Linux?

Linux is an operating system loosely based on UNIX, a popular mainframe operating system which was originally developed in the 1960s by AT&T's Bell Laboratories.  This is why Linux is often referred to as a "UNIX-like" operating system.

Also see Oracle Linux distributions.

Just like Microsoft Windows, Linux controls the computer hardware, does it's best to keep all your devices playing nicely together and gives you an interface to run things on the computer.  Unlike Microsoft Windows there are several groups (some commercial, some non-profit) who make Linux operating systems.

A Short History of Linux

Having a little background on Linux helps to understand why things are the way they are. Originally written in 1991, Linux is a relatively young operating system compared to its UNIX counterparts that have their origins in the late 1960s. The Linux kernel, the core of any Linux operating system, was conceived, created, and named after Linus Torvalds.

Linus? intent was to create a free operating system for himself and other hobbyists. Soon after Linus announced his project, several other software developers started to contribute code to the Linux kernel
and port software to compile it to work with the Linux kernel.Interest in the project skyrocketed and many formal releases of Linux followed. Linux gained popularity as more tools and capabilities were introduced, especially among educational institutions.  

Today Linux has found applications from education to industry and in devices ranging from supercomputers to television remote controls.A fairly early version of the Linux kernel has been distributed under the GNU (General Public License)
that allows it to be used at no cost for free or commercial projects. Linus Torvalds still oversees code changes to the Linux kernel, but today Linux development goes far beyond the kernel.

The Linux kernel is typically packaged into a distribution, often referred to as a distro, of Linux to provide a full set of tools for a specific purpose. The tools shipped with a Linux distro vary quite a bit and include compilers, web servers, graphical interfaces and an array of command line tools. 

Of the hundreds of Linux distributions, only a few are appropriate for running Oracle databases and those are the ones that will be focused on in this book.Through the years, UNIX operating systems, e.g. Solaris, AIX, and HP/UX, have enjoyed considerable popularity with servers due to their stability and inherent ability to serve multiple users and multiple applications simultaneously.

Linux shares these features, but is referred to as a UNIX-like operating system as it is not certified as or necessarily completely compliant with the standard tools and interfaces defined within the Single Unix Specification.

Choosing the Right Linux for Oracle

A top-down approach is best for choosing the right Linux for your your application.  Start with the requirements of the software that will be used on the system, then consider the requirements of the appropriate database version, which is probably dictated by the application.There are three layers to be concerned with when configuring a system: the platform, which refers to the type and capability of the server hardware, the distribution (distro)of Linux, and the version. Oracle supports a small handful of options for each of these layers.

Choosing the best Hardware Platform for Oracle Linux

The first concern is the hardware platform
you intend to use. The most popular hardware platforms are the x86 and x86_64platforms that use hardware derived from the popular Intel series of PC processors.  The x86_64 platform represents hardware capable of more advanced 64-bit processing.  x86_64 has become popular in servers and is gaining popularity in desktop systems.
Note: Historically, 32-bit platforms were limited to addressing 4 GB of memory.  There are acceptable workarounds that allow the DBA to address up to 64 GB of memory, but 64-bit Linux can natively address these larger memory sizes and offers other performance advantages.

Older versions of Oracle that support Linux are on several other hardware platforms including PowerPC, Itanium and zSeries, but as of the writing of this book, Oracle 11g on Linux is only supported on the x86 and x86_64 hardware platforms.

The Linux kernel

The heart of a Linux system is a program called the kernel.  The kernel controls security, processors, memory, disk and everything else about the system.

The kernel is what allows multiple users to be on a Linux system at the same time running dozens, possibly even thousands of things at once without interfering with each other.  While we won't talk too much more about the kernel, it's just important to remember that it's there keeping everything in check.

The Many Breeds of Linux

You may have already noticed that there are a ton of different Linux versions out there.  Many meet only a very specific need while others compete in the mass market for servers and workstations.  Here are a couple of the Linux distributions which are popular right now:

Red Hat Enterprise Linux  - This is the commercial version of Linux used for the examples in this book.  It is a popular option for both servers and workstations because it is both feature-rich and well supported.

Fedora  - Sponsored by Red Hat, this community supported version of Linux is available for free.  The free price tag makes this a great version to work with if you don't have (or want to pay for) a license for Red Hat Enterprise Linux, but be careful, some applications which are Red Hat compatible may not work on Fedora.

Ubuntu  - Ubuntu is a Linux-based operating system which has recently gained some popularity.  It is easy to install and the desktop version comes with many of the applications you would want on your workstation.

Mileage May Vary

Because no two distributions are quite the same you may find that some commands and options may not work, or may not work as described on your variety of Linux.  The examples in this book were done on RedHat Linux.  Almost all will work on most flavors of Linux but even a different version of RedHat will vary some.

Installation of Linux varies from distribution to distribution.  If you do not already have a Linux system to work on you may want to download one of the versions mentioned above and install it on a spare machine.  Unless you are experienced at installing Linux I suggest you choose a machine you will not use for anything else.  It is quite possible (even easy) to erase your entire hard drive while installing Linux, so take an old system (it doesn't have to be too fast) that you don't need any of the data on and follow the instructions that come with your distribution to install Linux.

What is a shell?

All the commands we run in this book are run in a Linux shell.  A shell in Linux is the software which allows you, a human, interact with the inner workings of the UNIX operating system.  Because of the shell we get to use commands that resemble our natural language (though sometimes only just barely) to control the behavior of the computer.  There are other types of shells in computing, but this is the only type we're concerned with for this book.

Beyond the ability to use somewhat intuitive commands individually, the shell also gives us the ability to combine these commands into shell scripts.  A shell script can contain one command or hundreds and the commands could be nearly anything you could do from within the shell.

The bash shell

There are, of course, many kinds of shells.  Each has its strengths and weaknesses but we're mostly concerned with the Bourne-Again Shell (bash) which is the default for users in Linux.

If you think your shell may not be bash don't worry.  We'll talk about how to change it later, but for now you can change it temporarily simply by typing bash.

Getting to the shell

You can access a Linux shell in several different ways.  You may access the shell by sitting at a Linux computer where the shell is displayed on screen or you may use a secure protocol to enter a shell on a system thousands of miles away.

In some environments you may use a telnet client or, more likely a secure ssh client to connect to a Linux machine.  This will depend largely on how you your machine and your environment is set up.  If you are connecting remotely through one of these clients you should talk with the person who set the machine up to find out how to connect.

Once you're at the Linux command line almost everything works the same whether you're at the keyboard of the system you work on or at a workstation half way around the world.

A few quick tips

Here are a few things that it might help you to know from the beginning.  They may seem out of place here, but will make more sense as we get into using Linux.

No news is good news

One thing you will have to get used to is that when you run many common Linux commands if things go right you will not get any feedback.  There are very few Linux commands which will tell you "Operation completed successfully."  More likely they will tell you nothing unless something goes wrong.  So basically don't worry if you don't get any feedback from Linux.  It'll give you an error if there's a problem.

Tab completion

One feature of the bash shell that we will be using is the ability to complete partially typed commands and file names with the tab key.  If you type in enough of the command or file to uniquely identify what you're looking for, then press tab Linux will complete the file or command.  Try it out once we get started.  It can save you a lot of typing.

Repeating recent commands with the up arrow

If you want to repeat a recently executed command, or even repeat it with a slight modification, the bash shell will allow you to recall it using the up arrow.  The up and down arrows will allow you to go back and forth through your recently typed commands to recall them for execution.  This can be very useful if you make a typo and don't want to retype the entire command again.

Getting More Help

While we will cover a lot of ground in this book you may find topics here which you want to learn more about.  Linux provides a couple resources available right at the command line to give you more information on commands.

Man Pages

Whenever detailed help is needed with command syntax or with command options, the manual (man) command can be used to display all of the information about the specified command. The information will be displayed one screen at a time. Pressing the space bar will advance the next screen. At the end of the display, the Q command can be used to quit.

The man command should be followed by the name of the command with which help is needed, as shown in the following example:

$ man w 

W(1)                          Linux User's Manual                         W(1)
       w - Show who is logged on and what they are doing. 

       w - [husfV] [user]


       w  - displays  information  about the users currently on the machine, and
       their processes.  The header shows, in this order,  the  current  time,
       how  long  the  system  has  been running, how many users are currently
       logged on, and the system load averages for the past 1, 5, and 15 minutes.

The  following entries are displayed for each user: login name, the tty name,
the remote host, login time, idle time, JCPU, PCPU, and the  command line
of their current process.

The  JCPU  time  is the time used by all processes attached to the tty.  It does
not include past background jobs, but  does  include  currently running background jobs.

The  PCPU  time  is  the time used by the current process, named in the "what" field.

Command Line Options



Don't print the header. 


Ignores the username while figuring out the current process and cpu times. To demonstrate this, do a "su" and do a "w" and a "w -u". 


Use the short format.  Don't print the login time, JCPU or PCPU times.


Toggle printing the from (remote hostname) field.  The default as released is for the from field to not be printed, although your system administrator or distribution maintainer may have compiled a version in which the from field is shown by default.



Display version information. 


Show information about the specified user only.



              information about who is currently logged on

        /proc  process information

The man pages can be a bit confusing but they will often contain options which are not covered in this book.  Be careful when using a new option for any command.


In situations where users are unsure which command should be used for a particular function, the info command can be used. The info subsystem contains information about all of the commands and utilities available within the system. The info system even gives tips for navigating within the info subsystem. The info command is entered to simply invoke the info subsystem.

The info subsystem even offers the capability of entering information about any commands, scripts, etc. for documentation purposes.

Get the Complete Details on
Linux System Management for Oracle DBAs  

The landmark book "Linux for the Oracle DBA: The Definitive Reference" provides comprehensive yet specific knowledge on administering Oracle on Linux.   A must-have reference for every DBA running or planning to run Oracle on a Linux platform.

Buy it for 30% off directly from the publisher.




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