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What is Linux?

Linux is an operating system that can be downloaded free and "belongs" to an entire community of developers, not one corporate entity. In other words, anyone from professional software developers to hobbyist computer hackers can access and make changes to the Linux kernel—all the information about Linux is open and available to everyone. That's why Linux is known as "open source" or "free software," because there is nothing secret about this system. This freedom also allows companies to sell and distribute Linux on CD-ROM or by other means, although those companies must keep their code open to the public.

With more and more people looking for an alternative to Windows, Linux has recently grown in popularity and is quickly becoming a favorite among major corporations and curious desktop users. Not only does it give users a choice of operating systems, it also proves itself valuable with its power, flexibility, and reliability.

Basic Linux Commands
Linux Installation
Linux Files and File Permission
RAID and LVM (Backup)

Basic Linux Commands



Cat Sends file contents to standard output. This is a way to list the contents of short files to the screen. It works well with piping.
cd Change directory
cp Copy files
dd Disk duplicate. The man page says this command is to "Convert and copy a file", but although used by more advanced users, it can be a very handy command. The "if" means input file, "of" means output file.

df Show the amount of disk space used on each mounted filesystem.
less Similar to the more command, but the user can page up and down through the file. The example displays the contents of textfile.
ln Creates a symbolic link to a file.
locate A fast database driven file locator.
logout Logs the current user off the system.
ls List files
mv Move or rename files
pwd Show the name of the current working directory
shutdown Shuts the system down.
whereis Show where the binary, source and manual page files are for a command

Linux Installation

Workstation - For no or minimal networking. Only client services is installed, so if you use this installation, don't expect to telnet to your system since the service was not installed. Use this installation if you don't have a network card or will not want to provide any network services.

Server - Installs most packages.

Custom - Allows you to select the packages you want to install. This is the selection I normally make. If you are planning on providing services such as telnet, mail, or web services, do a server or custom install. I usually install all packages with the exception of foreign language how tos. Unless disk drive space is limited .

Partition sizes

Swap partition - The swap partition, I usually make 128Mb. The recommendation is that the swap partition be twice as large as RAM memory or greater. In the past Linux could not use swap partitions larger than 128MB but the size limitation depends on your system's architecture.

Native Partition - If you are setting up a computer you will be learning Linux on or installing several operating systems, you may want one Linux native partition per Linux install. If, however, you are setting up a dedicated high performance server, you may want to set up several Linux native partitions and install various parts of the operating system on separate ones similar to the following recommendation or some modification thereof:
/ - Root size of 100MB

Linux Files and File Permission

Linux files are setup so access to them is controlled. There are three types of access:

1. Read
2. Write
3. Execute

Each file belongs to a specific user and group. Access to the files is controlled by user, group, and what is called other. The term, other, is used to refer to someone who is not the user (owner) of the file, nor is the person a member of the group the file belongs to. When talking about setting permissions for "other" users to use, it is commonly referred to as setting the world execute, read, or write bit since anyone in the world will be able to perform the operation if the permission is set in the other category.

RAID and LVM (Backup)

RAID is usually defined as Redundant Array of Inexpensive disks. It is normally used to spread data among several physical hard drives with enough redundancy that should any drive fail the data will still be intact. Once created a RAID array appears to be one device which can be used pretty much like a regular partition. There are several kinds of RAID but I will only refer to the two most common here.

The first is RAID-1 which is also known as mirroring. With RAID-1 it's basically done with two essentially identical drives, each with a complete set of data. The second, the one I will mostly refer to in this guide isRAID-5 which is set up using three or more drives with the data spread in a way that any one drive failing will not result in data loss. The Red Hat website has a great overview of the RAID Levels.

There is one limitation with Linux Software RAID that a /boot partition can only reside on a RAID-1 array. Linux supports both several hardware RAID devices but also software RAID which allows you to use any IDE or SCSI drives as the physical devices. In all cases I'll refer to software RAID.

LVM stands for Logical Volume Manager and is a way of grouping drives and/or partition in a way where instead of dealing with hard and fast physical partitions the data is managed in a virtual basis where the virtual partitions can be resized. The Red Hat website has a great overview of the Logical Volume Manager. There is one limitation that a LVM cannot be used for the /boot.

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