Linux has some special attributes associated with all files. Often in X Windows when you check the properties of any file (by right clicking on it and viewing its properties) you would get to see 3 special attributes besides the common read/write/execute rights for the owner/group/others . The 3 extra attributes are known as SUID, SGID and Sticky Bits
Continue reading ‘What are the SUID, SGID and the Sticky Bits?’

This article explains 2 simple commands that most people want to know when they start using Linux. They are finding the size of a directory and finding the amount of free disk space that exists on your machine. The command you would use to find the directory size is ‘ du ‘. And to find the free disk space you could use ‘ df ‘.

All the information present in this article is available in the man pages for du and df. In case you get bored reading the man pages and you want to get your work done quickly, then this article is for you.

Continue reading ‘How to find – Size of a directory & Free disk space’

Linux is basically a multi-user system. But nowadays there has been an increase in the usage of Linux as an OS for single user home computers as well. But since it was originally meant to be a multi-user OS, a lot of things that would be necessary in a multi-user system are built into the Linux core. One such thing is file / directory permissions.

In Linux every file present on the disk has associated permissions with it. These permissions decide on who and in what manner these files should be used. The rest of this article explains these file / directory permissions in details.

Continue reading ‘Understanding file permissions and modifying them using chmod’

In Linux the command line interpreter is known as the shell. Whatever you type at the command line is understood and interpreted by a program and then that program gives you an output after executing your command. This program that understands what you type is called the shell.

Linux comes with quite a few shells such as Bourne Shell, Bourne Again Shell, C Shell, Korn Shell, etc. The default shell for Redhat Linux is ‘ bash ‘ which is very popular since being the default, most users start by learning bash. I shall talk about the bash shell only in this article.

Windows users would be familiar with a program called which had to be present for the OS to boot. is the Windows equivalent of the Linux shell. Continue reading ‘How to set Shell Environment Variables (bash shell)’

This article deals with 2 issues which are many a times used with each other. The first one is about wildcards and the other one is the use of special characters while typing commands at the shell prompt.

I call this a Special Guide since the information in this article helps you with many of your commands and is not restricted to any particular application as such. Thus reading this article is a must for all Linux users.

In Linux whenever you are not sure about the name of a file and you want to do something with files such as either search for them or copy them or delete some files based on some knowledge you have about the filenames then you can use Wildcards. Wildcards are basically an indicator to the shell that some particular part of the filename is not known to you and the shell can insert a combination of characters in those places and then work on all the newly formed filenames. This concept would be clear by the end of this article

Continue reading ‘Wildcards, Quotes, Back Quotes and Apostrophes in shell commands ( * ? [] ” ` ‘)’

In this second article, Harold continues with his fast paced, excellent introduction to Bash Programming. This time he explains how to perform arithmetic operations in your bash scripts. He also explains how to define functions in your programs. Finally he concludes with an introduction to advanced concepts such as reading user inputs in your bash scripts, accepting arguments to the scripts, trapping signals and also understanding return values of programs.

This is definitely much more than you must have expected… Once you read this you would no longer be a beginner.. you would already be on your way to master Bash programming!! Continue reading ‘A Quick Introduction to Bash Programming – Part 2’

Bash programming is a topic that can be dealt with in a couple of pages or hundreds of pages. Harold Rodriguez explains Bash programming in this 2 Part tutorial. His slick and excellent style of writing has enabled him to cover all the essential features of bash programing in a few pages.

If you have never programmed in Bash before, this is the best place to begin. In case you have a little knowledge of bash, then too you could have a look.. a lot of interesting scripts have been explained by Harold. Continue reading ‘A Quick Introduction to Bash Programming – Part 1’


Each file in Linux inherits a set of properties.  One vital set of properties is the file’s permissions.  Permissions determine what any particular user (or group of users) is able to do that file.  File permissions help prevent unwanted deletion and safeguard your data.  In order to use Linux’s file permissions, you need to understand Linux’s categories of users and groups.

Categories of Users

You are asked to enter a login name and password when you first log into Linux.  When we talk of a user, we refer to the account issuing commands to the operating system at the time and not to the actual person operating the computer.  As soon as Linux authenticates your login name and password you “become” that user and operate using that user account.

Users belong to one or more groups. (The SuperUser allocates Users to particular groups.)  Each user has a default group. Continue reading ‘About File Permissions’

By Alex Garner.

How do I know what size to make my disk partitions?

This is one of the more often asked questions I hear. Usually the answer is “It depends”, so here is my experience with partitioning Linux boxes for various applications over the last few years.

First of all it helps to know exactly what the file systems are all used for and where stuff goes. A good reference for this sort of thing is in the Linux Documentation Project’s “System Administrator’s Guide” or SAG. You can find a good bit of info on the file system here

Alternatively, if you have a copy of “A Practical Guide to Linux”, then check out page 74. Continue reading ‘Disk Partitioning’


This document explains how to set your computer’s clock from Linux, how to set your timezone, and other stuff related to Linux and how it does its time-keeping.

Your computer has two timepieces; a battery-backed one that is always running (the “hardware”, “BIOS”, or “CMOS” clock), and another that is maintained by the operating system currently running on your computer (the “system” clock). The hardware clock is generally only used to set the system clock when your operating system boots, and then from that point until you reboot or turn off your system, the system clock is the one used to keep track of time.

On Linux systems, you have a choice of keeping the hardware clock in UTC/GMT time or local time. The preferred option is to keep it in UTC because then daylight savings can be automatically accounted for. The only disadvantage with keeping the hardware clock in UTC is that if you dual boot with an operating system (such as DOS) that expects the hardware clock to be set to local time, the time will always be wrong in that operating system. Continue reading ‘Linux, Clocks, and Time’

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