My Linux Guide (Page 3)

Linux Kernel Initialization

Kernel initialization ————————- .kernel detects the attached devices in the system & loads thier drivers into RAM. .mounts root filesystem into read-only memory mode. .Then initializes the ‘init’ process for further processing init=it is the first process that is started at the boot time. –init initialization /etc/inittab – main

Systems Administrator

Linux Boot process, system initialization

System Initialization & Services –> Boot sequence i. BIOS initialization ii. Boot Loader initialization iii. Kernel initailization iv. init initialization Power on –> BIOS —-> BOOT LOADER(MBR) –> KERNEL–>init Kernel- Monolithik kernel -Boot Loader i. Grub (Grand Unified Boot loader) (latest) ii. LILO (Linux Loader) (old)

Linux Installation Guide

Hardware: redhat.com/HCL (information about redhat supported hardware) http://www.xfree86.org (to check graphics compatibility e.g. VGA card, monitor) http://www.redhat.com/support/errata /bug-fixes Redhat supported architechre * RHEL supports the following cpu architechures .intel’s x86 arch. . interl’s Itanium ,, . AMD64 . IBM’s s/390,

Vi & String Processing

String processing with regular expressions

String Processing with regular expression * Regular Expression . Regular expression is a pattern matching engine. . It is used by different tools like vi, grep, sed, awk etc. * Modifiers . It determines the no. of previous character. Modifier Meaning * – Matches zero or more of the previous char. \+ – ,, one ,, ,, ,, ,, ,, ,, \? – ,, zero or one of the

Graphical User Interfaces in Linux

GNOME/KDE/X-window system ————————— – X-window system . It is the main GUI component of linux. . It is based on client/server Architechure. . Applications are called x-clients & display is called x-server. . x-cleints communicates with x-server using x-protocol. . x window system was developed by Athena project of MIT; now handled by xc-consortium.

Introduction to Processes

Introduction to process ————————– What is a process? ——————— .Each running application is called a process. .Each process are identified by a no. called preocess idification no. (PID) .PID of ‘init” process is always 1. init= it is the first process that is started at boot time., it is called also grand

Introduction to Shell Scripting

Bash Shell scripting ——————— -What is a shell script? . Shell script is a normal text file that contains commands to perform some specific tasks. .Shell scripting is extensively used in system administration to automate routine task like creating backup, scanning disks etc. .Shell scripts are also used to create simple applications.

Linux Shell Basics

The bash shell: Sh: Bourne shell, developed by Steven Bourne in AT & T lab. -A traditional unix shell. Csh: C shell, C programming language was used.Developed by Bill Joy (many features such as: -command line complition -command line editing -History of command for each user is mantained. Ksh:

Finding Files and Directories

finding files and directories Find command searches for files and directories as per the defined criteria. find command also searches inside the sub-dir of specified path. Syntax: find [path] <criteria> <action> path=where to search Criteria can be: -name <filename> [name based search] -iname

Calculating Default Permissions

Calculating default permission 1. file – Maximum allowed permission at the time of file creation (666) -umask Default permission on a file 0022 1st zero is special permission 2nd zero is owner perm. 2. Directory Max. allowed permission at the time if dir creation (777) Default permission on a dir. Questions:

Color Codes in Linux

Color codes ———– White color – Normal text file Blue Dir Green Executable file (.exe,.com,bat..bash etc) Cyan Symbolic link Yellow devie file Red Compressed file or archive file (.gx,.bz2,tar etc) Magenta Picture file (.jpg.bmp.xpm etc) Location of file /etc/DIR_COLORS

User Groups and Permissions

– Users Types: UID 1. Root user 0 2. System users 1-499 3. normal users >500 /etc/passwd – User database format Username:x:UID:GID:<comment>:home_dir:shell X=Encricpted password (/etc/shadow) Groups Types: GID 1. Root users group 0 2. System User group 1-499 3.

Vi & String Processing

Vi Editor

The VI editor The standard Unix/Linux editor -Now we have vim-improved with move feature. -When Vi is used system invokes ‘Vim’ because vi is defined alias to vim. Starting: # Vi filename (Open an existing file or editing or a new file is created if the current buffer is saved)

Sorting

sorting is the arrangement of data/information in increasing (ascending) or decreasing(descending) pattern. #sort <options> filename Options: -r -reverse order -n -numeric order -t -as field separator, delimiter -k position -u unique sort #sort /etc/passwd #sort -r /etc/passwd #cut -d:-f7 /etc/passwd|sort -u

Vi & String Processing

Introduction to string processing

Introduction to string Processing Head/Tail Head and tail command are used to view the first and last few lines of a file respectively. By default these commands generate 10 numbers of lines. # head /etc/passwd (shows first 10 lines) # tail /etc/passwd (shows last 10 lines) One very handful

Shell Scripting

Reading an Input From File

Reading an input from a file: Command <file> #tr ‘a-z’ ‘A-Z <file (Translates all the lowercase characters to uppercase). Note: if you want to print the output of existing file to new file Use this command #tr `a-z’ `A-Z'<oldfilename>newfilename

Input Output Pipes and Redirection

Input, Output and pipes: Standard output-Terminal screen is default Standard error -Terminal screen is default Standard input = Keyboard is default Redirectional operators: Command > file1 (writes the standard output from command to file1) Command >> file1 (Appends the output from command to file1) Command 2>file2 (Writes the

Systems Administrator

Archiving and Compression

Archiving and compression at the time: Syntax: tar <option> files/dir Options: Z (if we are using gzip compression) j (if we are using bzip2) x (Extracts) v (verbose mode) f (for archived file) t (list the content of an archived file) # tar zcvf gvn.tar.gz /etc

Systems Administrator

Backup Master Boot Record

dd if=/dev/sda of=/tmp/mbr.img bs=512 count=1

Shell Scripting

Time Saving CLI Techniques

$ echo {x,y,z} x y z $ echo a{x,y,z} ax ay az $ echo {{1,2,3},1,2,3} 1 2 3 1 2 3 $ echo {{1,2,3}1,2,3} 11 21 31 2 3 $ cp /etc/samba/smb.conf{,.bak} >CTRL + R to

Shell Scripting

Simple yes no input shell script

Simple shell script to get user confirmation echo “Do You wish to Continue ?<y/n>: ” read response if [ $response = “y” ];then echo “You entered yes” echo “Please Wait..Window Will Close When Done” sleep 10 ……………… echo “Done…Exiting Now” sleep 2 …………………. exit fi

Shell Scripting

Disable Traps ctrl c , ctrl z in shell script

Use the following line in the beginning of your shell script to disable traps like ctrl c and ctrl z in your shell script. trap “” 2 20

Shell Scripting

Protect Shell scripts

http://www.datsi.fi.upm.es/~frosal/sources/shc.html

Systems Administrator

Using Crontab

CRON TABLE is used to execute tasks in unix,solaris operating systems. IT is used to execute scheduled tasks at specific times. Two files : /usr/lib/cron/cron.allow and /usr/lib/cron/cron.deny determine who can and cannot use the cron jobs. If only cron.deny file exists

DNS

Master DNS Configuration in Chrooted Environment

Here is a little tutorial on how to configure bind in chrooted environment. 1. First of all you need to install all the required packages. #yum install bind bind-chroot bind-libs bind-utils caching-nameserver 2. Configure RNDC.key file. This key file is required for secured communication between master and slave DNS