Linux Tutorial

Ken Thompson and Dennis Ritchie of Bell Laboratories developed the UNIX operating system in 1969. It was later rewritten in C.

A Linux system is divided into three main parts:

Hardware - This includes all the hardware, memory, CPU, disks, etc.
Kernel - kernel is the core of the operating system. It manages the hardware and tells it how to interact with the system.
User Space - This is where users like yourself will be directly interacting with the system.

1. Linux Distributions

Operating systems like Microsoft combine each bit of codes internally and release it as a single package. You have to choose from one of the version they offer (Win98, XP, Win 7, Win 8, Win 10 etc.)

Linux is different, Different parts of Linux (kernel, shell utilities, X server, system environment, graphical programs, etc.) are developed by different organizations. But it’s not an easy task to assemble the parts correctly. From here on distribution (also called as distros) comes into the picture.

Distros will assemble all these parts for us and give us a compiled operating system of Linux to install and use.

Distribution	Pros	Cons
RHEL& CentOS	Very stable and reliable; very well supported; used almost everywhere; very traditional layout and management approach	Very long release cycle; packages will be older and generally more difficult to bring to current if required
Fedora	Quite cutting-edge – sometimes bleeding-edge; lots of supported software with recent releases	Can be less than stable due to fast-paced package and release updates; generally thought to be Red Hat’s testing distribution
Ubuntu	Solid release cycle based on LTS (Long Term Support) and intermediate releases; user friendly, with lots of -helper” commands	Tends to move quickly and packages can be less stable than others; has unique conventions that don’t translate to other distributions
Debian	Very stable and reliable; wide variety of support packages; all-volunteer maintainers; supports large variety of architectures	Very conservative; release cycle can be slow
openSUSE	Stable, solid distribution; plenty of support packages; has sys admin tools such as YaST	Has been stunted by Novell’s acquisition and dealings with Microsoft that assume rights over portions of Linux; has unique sys admin tools such as YaST

2. Linux Features

Multiuser capability: Multiple users can access the same system resources like memory, hard disk, etc. However, they have to use different terminals to operate.

Multitasking: More than one task can be performed simultaneously by dividing the CPU time intelligently.

Portability: it supports different types of hardware.

Security: It provides security in three ways namely authenticating (by assigning password and login ID), authorization (by assigning permission to read, write and execute) and encryption (converts file into an unreadable format).

Application support: It has its own software repository from where users can download and install many applications.

File System: Provides hierarchical file system in which files and directories are arranged.

Open Source: Linux code is freely available to all and is a community based development project.

3. Unix Vs Linux

Some people think UNIX and Linux are same, but that is not true. Many operating systems were developed to be like UNIX but none of them got the popularity as Linux.

Linux is the clone of UNIX. It has several features similar to UNIX, still have some key differences. Before Linux and Windows, UNIX dominated computer world.

Comparison	Linux	Unix
Definition	It is an open-source operating system, which is freely available to everyone.	It is an operating system, which can be only used by its copyrighters.
Examples	Ubuntu, Redhat, Fedora, etc.	IBM AIX, HP-UX and Sun Solaris.
Users	Anyone can use Linux like home user, developer or a student.	It was developed mainly for servers, workstations and mainframes.
Usage	Used everywhere from servers, PC, smartphones, tablets to supercomputers.	used in servers, workstations& PCs.
Cost	Linux is freely distributed, downloaded.	Unix copyright vendors decide different costs for their respective Unix OS’s
Manufacturer	The community of developers from different parts of the world develops Linux kernel. Although the father of Linux, Linus Torvalds oversees things.	Unix has three distributions IBM AIX, HP-UX and Sun Solaris. Apple also uses Unix to make OSX operating system.
Operating system	Linux is just the kernel.	Unix is a complete package of Operating system.
Security	It provides higher security. Linux has about 60-100 viruses listed till date.	Unix is also highly secured. It has about 85-120 viruses listed till date
Error detection and solution	As Linux is open-source, whenever a user post any kind of threat, developers from all over the world start working on it. Hence, it provides faster solution.	In Unix, users have to wait for some time for the problem to be resolved.

4. Linux Commands

A command is an instruction given to our computer by us to do whatever we want. In Mac OS, and Linux it is called terminal, whereas, in windows it is called command prompt. Commands are always case sensitive.

Commands are executed by typing in at the command line followed by pressing enter key

There are two types of shell commands

Built-in shell commands: They are part of a shell. Each shell has some built in commands.
External/Linux commands: Each external command is a separate executable program written in C or other programming languages

2.Linux File System

$E:\Users\satyacodes\Pictures\12.png$

All the directories in the Linux system comes under the root directory which is represented by a forward slash (/)

$E:\Users\satyacodes\Pictures\12.png$

Command	Full Form	Description
pwd	Present Working Directory	Displays the current working location or directory of the user complete path starting with /. It is a built-in command.
cd	Change Directory	It is used to change to the directory you want to work from the present directory.
ls	List	The ls command is used to show the list of a folder. It will list out all the files in the directed folder.
mkdir	Make Directory	With mkdir command, you can create your own directory.
rmdir	Remove Directory	The rmdir command is used to remove a directory from your system.

1. pwd Example

Linux pwd (print working directory) command displays your location currently you are working on. It will give the whole path starting from the root ending to the directory

[smlcodes@centori ~]$pwd
/home/smlcodes

2. cd Example

The “cd” stands for ‘change directory’ and this command is used to change the current directory i.e.; the directory in which the user is currently working.

[smlcodes@centori ~]$cd java/                                                    
[smlcodes@centori java]$pwd                                                      
/home/smlcodes/java                                                              
[smlcodes@centori java]$

cd Options

option	Description
cd ~	Brings you to your home directory.
cd -	Brings you to your previous directory of the current directory.
cd ..	Brings you to the parent directory of current directory.
cd /	It takes you to the entire system’s root directory.
cd ../ ../dir1/dir2	It will take you two directories up then move to dir1 and then finally to dir2.

3. ls Example

The ls is the list command in Linux. It will show the full list or content of your directory.

[smlcodes@centori ~]$ls
java  json  jsp  spring

Linux ls command options

ls option	Description
ls -a	list including the hidden files.
ls -l	It will show the list in a long list format.
ls -lh	This command will show you the file sizes in human readable format. Size of the file is very difficult to read when displayed in terms of byte. The (ls -lh)command will give you the data in terms of Mb, Gb, Tb, etc.
ls -lhS	If you want to display your files in descending order (highest at the top) according to their size, then you can use (ls -lhS) command.
ls -l - -block-size=[SIZE]	It is used to display the files in a specific size format. Here, in [SIZE] you can assign size according to your requirement.
*ls -d /**	It is used to display only sub directories.
ls -g or ls -lG	With this, you can exclude column of group information and owner.
ls -n	It is used to print group ID and owner ID instead of their names.
ls –color=[VALUE]	This command is used to print list as colored or discolored.
ls -li	This command prints the index number if file in the first column.
ls -p	It is used to identify the directory easily by marking the directories with a slash (/) line sign.
ls -r	It is used to print the list in reverse order.
ls -R	It will display the content of the sub-directories also.
ls -lX	It will group the files with same extensions together in the list.
ls -lt	It will sort the list by displaying recently modified filed at top.
ls ~	It gives the contents of home directory.
ls ../	It give the contents of parent directory.
ls –version	It checks the version of ls command.

4. mkdir Example

To make Single directory one by one
[smlcodes@centori ~]$mkdir java
[smlcodes@centori ~]$mkdir jsp
 [smlcodes@centori ~]$mkdir json

To make multiple directories
Syntax: mkdir <dir1> <dir3>…<dir-n>
[smlcodes@centori ~]$mkdir j1, j2

mkdir Options

Options	Description
mkdir -p, -parents	Add directory including its sub directory.
mkdir -v, -verbose	Print a message for each created directory.
mkdir -m -mode=MODE	Set access privilege.

5.rmdir Example

Delete a single file

[smlcodes@centori ~]$rmdir json/                                                 
[smlcodes@centori ~]$ls                                                          
java  jsp  spring

rmdir –p : delete a directory including its sub-directories

3.Linux Files

In Linux, everything is consider as a file, not only text files, images but also system partitions are also treated as files.

We have following types of files in Linux

Regular files (-): It contain programs, executable files and text files.
Directory files (d): It is shown in blue color. It contain list of files.
Special files
- Block file (b)
- Character device file (c)
- Named pipe file (p)
- Symbolic link file (l)
- Socket file (s)

To work with files, we have following commands

Command	Description
file	Determines file type.
touch	Used to create a file.
rm	To remove a file.
cp	To copy a file.
mv	To rename or to move a file.
rename	To rename file.

3.1 -file” command

The file command is used to determine a file’s type. The type printed will usually contain one of the words text (ASCII), executable or data.

Syntax: file <filename>

Example
[smlcodes@centori ~]$file a.txt                                                  
a.txt: ASCII text

File command tell us the file type with the help of a magic file that contains all the patterns to recognize a file type. Path of magic file is /usr/share/file/magic. For more information, enter the command ‘man 5 magic’.

Linux File Command Options

Option	Function
file *	Used to list types of all the files.
file /directory name*	Used to list types of all the files from mentioned directory.
file [range]*	Lists files starting from the alphabet present within the given range.

Examples

[smlcodes@centori files]$pwd
/home/smlcodes/files

[smlcodes@centori files]$file *
a.txt:       ASCII text
a.xtx:       ASCII text
b.txt:       ASCII text
img2.jpng:   ASCII text
img.png:     ASCII text
rarfile.rar: empty
special:     directory
zipfile.zip: empty

[smlcodes@centori files]$file /home/smlcodes/files/special/*
/home/smlcodes/files/special/s1.txt: empty
/home/smlcodes/files/special/s2.txt: empty

[smlcodes@centori files]$file [a-m]*
a.txt:     ASCII text
a.xtx:     ASCII text
b.txt:     ASCII text
img2.jpng: ASCII text
img.png:   ASCII text

3.2 -touch” command

The touch command is the easiest way to create new, empty files. It is also used to change the timestamps (i.e., dates and times of existing files and directories).

Syntax 
touch [option] file_name(s)

Example
[smlcodes@centori files]$touch 1.txt

To create multiple files just type all the file names with a single touch command

[smlcodes@centori files]$touch file1, file2, file3                               
[smlcodes@centori files]$ls
1.txt  a.xtx  file1,  file3      img.png      special
a.txt  b.txt  file2,  img2.jpng  rarfile.rar  zipfile.zip

touch Options

Option	Full Form	Function
touch -a	Access	To change file access and modification time.
touch -m	Modify	It is used to change only modify time of a file.
touch -r	Reference	To update time of one file with reference to the other file.
touch -t	With Time	To create a file by specifying the time.
touch -c	-	It does not create an empty file.

Examples

Touch –a , to see the time stamp we use stat command

[smlcodes@centori files]$stat a.txt 
  File: ‘a.txt’
  Size: 105             Blocks: 8          IO Block: 4096   regular file
Device: 811h/2065d      Inode: 3736598     Links: 1
Access: (0664/-rw-rw-r--)  Uid: (79458/smlcodes)   Gid: (79459/smlcodes)
Context: guest_u:object_r:user_home_t:s0
Access: 2017-08-01 08:05:59.706000000 +0200
Modify: 2017-08-01 07:57:44.409000000 +0200
Change: 2017-08-01 07:57:44.414000000 +0200
 Birth: -

[smlcodes@centori files]$touch -a a.txt                                          
[smlcodes@centori files]$stat a.txt                                              
  File: ‘a.txt’
  Size: 105             Blocks: 8          IO Block: 4096   regular file
Device: 811h/2065d      Inode: 3736598     Links: 1
Access: (0664/-rw-rw-r--)  Uid: (79458/smlcodes)   Gid: (79459/smlcodes)
Context: guest_u:object_r:user_home_t:s0
Access: 2017-08-01 08:23:36.216000000 +0200
Modify: 2017-08-01 07:57:44.409000000 +0200
Change: 2017-08-01 08:23:36.216000000 +0200
 Birth: -
[smlcodes@centori files]$

3.3 -rm” (remove) command

The rm command removes (deletes) files or directories. The command line doesn’t have a recycle bin or trash unlike other GUI’s to recover the files

Syntax:

rm <filename>

rm Options

Option	Description
*rm extension**	Used to delete files having same extension.
rm -r or R	To delete a directory recursively.
rm -i	Remove a file interactively.
rm -rf	Remove a directory forcefully.

Example

$E:\Users\satyacodes\Pictures\12.png$

3.4 -cp” (copy) command

The cp command is used to make copies of files and directories

Syntax

cp [OPTION] <SOURCE PATH> <DESTINATION PATH>

cp Options

Option	Function
cp -r	To copy a directory along with its sub dirctories.
cp file1 file 2 directory name	To copy multiple file or directories in a directory.
cp -backup	To backup the existing file before over writing it.
cp -i	Asks for confirmtion.
cp -l	To create hard link file.
cp -p	Preserves attribute of a file.
cp -u -v	To make sure source file is newer then destination file.

Examples

##### 1. cp <f1>,
[smlcodes@centori files]$pwd                                                     
/home/smlcodes/files                                                             
[smlcodes@centori files]$ls                                                      
a.txt  b.txt  folder1  folder2
[smlcodes@centori files]$cp a.txt 1.txt                                          
[smlcodes@centori files]$ls                                                      
1.txt  a.txt  b.txt  folder1  folder2


######## cp -r	To copy a directory along with its sub dirctories.
[smlcodes@centori ~]$cp -r files newfolder                                       
[smlcodes@centori ~]$ls                                                          
a.txt  files  j1,  j2  java  jsp  newfolder  spring
[smlcodes@centori ~]$cd newfolder/                                               
[smlcodes@centori newfolder]$ls                                                  
1.txt  a.txt  b.txt  folder1  folder2

3.5 -mv” (move) command

The mv command is used to move or rename files. mv renames file SOURCE to DEST, or moves the SOURCE file (or files) to DIRECTORY.

**Syntax:**
mv [OPTION]... SOURCE... DIRECTORY

mv Option

Option	Function
mv -i	Asks for permission to over write.
mv *	Move multiple files to a specific directory.
mv –suffix	Used to take backup before over writing.
mv -u	Only move those files that doesn’t exist.(replace with skip)

Examples

[smlcodes@centori files]$ls
1.txt  a.txt  b.txt  folder1  folder2
[smlcodes@centori files]$mv 1.txt 2.txt
[smlcodes@centori files]$ls
2.txt  a.txt  b.txt  folder1  folder2

[smlcodes@centori files]$mv -i 2.txt 3.txt
[smlcodes@centori files]$ls
2.txt  a.txt  b.txt  folder1  folder2

[smlcodes@centori files]$mv * /folder2
[smlcodes@centori files]$ls
2.txt  a.txt  b.txt  folder1  folder2

3.6 -rename” command

When you want to rename a large group of files at once then it will be difficult to rename it with ‘mv’ command. In these cases, it is adviced to use ‘rename’ command. It can convert upper case files to lower case files and vice versa and cn overwrite files using perl expressions

Syntax:
rename 's/old-name/new-name/'

rename options

Option	Function
rename -n	Check changes before running the command.
rename -v	Print the output.
rename (a-z)(A-Z)/ (A-Z)(a-z)	Convert into upper case/lower case.
rename -f	Forcefully over write existing files.

3.7 -man” (manual) command

We can see the manuals for a command with the man command. On Linux and other Unix-like operating systems, man is the interface used to view the system’s reference manuals

Syntax:
man [option(s)] keyword(s)

man Options

Commands	Function
man -aw	List all available sections of a command.
man -a	To view all man pages of a command.
sman -k (apropos)	Shows a list of results in man page containing a keyword match.
-f, whatis	It displays description from manual page if available.
whereis	Used to determine location of a man page

Example

man ls

$E:\Users\satyacodes\Pictures\12.png$

4.Linux File Content

There are many commands which help to look at the contents of a file. Below are cery frequently used commands on

Commands	Function
head	It displays the beginning of a file.
tail	It displays the last last part of a file.
cat	This command is versatile and multi worker.
tac	Opposite of cat.
more	Command line diaplays contents in pager form that is either in more format.
less	Command line diaplays contents in pager form that is either in less format.

1. -head” command

The ‘head’ command displays the starting content of a file. By default, it displays starting 10 lines of any file.

Syntax:

head

Option	Description
head ..	Displays First 10 lines of multiple files
head -n	Displays specified number of lines..
head -c	Counts the number of bytes of a file.

Examples

[smlcodes@centori ~]$head file.txt                                              
lin1 : sajjkldlkasjldasjlkdjlasdjasdjlas                                        
line2:sajkdasjkhdhsakhdaskhdaskj                                                
lin3 :sajdilsajdjsajldjasdjasdjlkas                                              
l4:askdhashkdhasdhkasdjkasdhk                                                    
l5:askdasdjkashdhashdkaskhdasjk                                                  
l6:sadjkhsajkdhasjkdhashkdhkasjdh                                                
l7:92378472384789234782379842379472                                              
l8:asljkdaskduqwioeru23o4u2390erj2                                               
l9:dsakdasioduo7820983902908302                                                  
line10:pioaseioqwpieqipweipqwo 

[smlcodes@centori ~]$head -2 file.txt                                            
lin1 : sajjkldlkasjldasjlkdjlasdjasdjlas                                         
line2:sajkdasjkhdhsakhdaskhdaskj

2. -tail” command

The ‘tail’ command displays the last lines of a file. By default, it will also display the last ten lines of a file

Syntax:

tail <file name>

Option	Description
tail ..	Displays last 10 lines of multiple files
tail -n	Displays specified number of lines from last
tail -c	Counts the number of bytes of a file.

Example

[smlcodes@centori ~]$tail file.txt                                               
line10:pioaseioqwpieqipweipqwo                                                   
lin11 : sajjkldlkasjldasjlkdjlasdjasdjlas                                        
line12:sajkdasjkhdhsakhdaskhdaskj                                                
 lin13 :sajdilsajdjsajldjasdjasdjlkas                                            
l14:askdhashkdhasdhkasdjkasdhk                                                   
l15:askdasdjkashdhashdkaskhdasjk                                                
l16:sadjkhsajkdhasjkdhashkdhkasjdh                                              
l17:92378472384789234782379842379472                                             
l18:asljkdaskduqwioeru23o4u2390erj2                                              
l19:dsakdasioduo7820983902908302                                                 
li20:sadjkasjkldlasjdlasjljl

3. -cat” (catenate) command

cat stands for “catenate.” It reads data from files, and outputs their contents. It is the simplest way to display the contents of a file at the command line.

cat is one of the most commonly-used commands in Linux. It can be used to:

Display text files
Copy text files into a new document
Append the contents of a text file to the end of another text file, combining them

//Display text files
cat <fileName>
[smlcodes@centori ~]$cat java.txt 
In java we have follwing concepts
- Java Colelctions
-Java Swings
-Servlts
-JSP


//Copy text files into a new document
cat sends its output to stdout (standard output), which is usually the terminal screen. However, you can redirect this output to a file using the shell redirection symbol ">".
cat mytext.txt > newfile.txt
[smlcodes@centori ~]$cat java.txt>a.txt                                          
[smlcodes@centori ~]$cat a.txt
In java we have follwing concepts
- Java Colelctions
-Java Swings
-Servlts
-JSP

Similarly, you can catenate several files into your destination file. For instance:
cat mytext.txt mytext2.txt > newfile.txt


Append the contents of a text file to the end of another text file
Instead of overwriting another file, you can also append a source text file to another using the redirection operator ">>".
cat mytext.txt >> another-text-file.txt
[smlcodes@centori ~]$cat a.txt>>java.txt
[smlcodes@centori ~]$cat java.txt 
In java we have follwing concepts
- Java Colelctions
-Java Swings
-Servlts
-JSP
In java we have follwing concepts
- Java Colelctions
-Java Swings
-Servlts
-JSP

Option	Function
cat > [fileName]	To create a file.
cat [oldfile] > [newfile]	To copy content from older to new file.
cat [file1 file2 and so on] > [new file name]	To concatenate contents of multiple files into one.
cat -n/cat -b [fileName]	To display line numbers.
cat -e [fileName]	To display $ character at the end of each line.
cat [fileName] «EOF	Used as page end marker.

4. -tac” command

The ‘tac’ command is the reverse of the ‘cat’ command. It is also known as ‘cat’ backwards. It will display the file content in reverse order.

Syntax:
tac <filename>


[smlcodes@centori ~]$tac a.txt
-JSP
-Servlts
-Java Swings                                                                     
- Java Colelctions                                                               
In java we have follwing concepts

5. -more” command

‘cat’ command displays the file content. Same way ‘more’ command also displays the content of a file. Only difference is that, in case of larger files, ‘cat’ command output will scroll off your screen while ‘more’ command displays output one screenful at a time.

Following keys are used in ‘more’ command to scroll the page:

Enter key : To scroll down page line by line.
Space bar : To go to next page.
‘B’ key : To go to the backward page.
‘/’ key : Lets you search the string. ```bash • ‘/’ key : Lets you search the string. Syntax: more

[smlcodes@centori ~]$more log.txt CAT(1) User Commands CAT(1) NAME cat - concatenate files and print on the standard output

SYNOPSIS cat [OPTION]… [FILE]…

DESCRIPTION Concatenate FILE(s), or standard input, to standard output.

   -A, --show-all
          equivalent to -vET
   -b, --number-nonblank
          number nonempty output lines, overrides -n

   -e     equivalent to -vE

   -E, --show-ends
          display $ at end of each line

   -n, --number
          number all output lines

   -s, --squeeze-blank                                                       
          suppress repeated empty output lines                               

   -t     equivalent to -vT --More--(32%) ```

6. -less” command

The ‘less’ command is same as ‘more’ command but include some more features.It automatically adjust with the width and height of the teminal window, while ‘more’ command cuts the content as the width of the terminal window get shorter.

Syntax:

less <filename>

7.”histrory”

It will gives the history of previously executed commands

[satya@centori \~]$history

dir

pwd

pwd

ls

mkdir java

mkdir jsp

mkdir spring

mkdir json

clear will clears the screen

5. Linux Pipes & Filters

Linux Filter commands accept input data from stdin (standard input) and produce output on stdout (standard output). It transforms plain-text data into a meaningful way and can be used with pipes to perform higher operations.

These filters are very small programs that are designed for a specific function which can be used as building blocks.

Linux Filter Commands

cat
cut
grep
comm
tee
tr
uniq
wc
od
sort
gzip

1.-cat” inside Pipes

When we use cat command inside pipes, it moves the stdin to stout.

Syntax:
cat <fileName> | cat or tac |  cat or tac |. . .

Example
[smlcodes@centori ~]$cat a.txt                                                   
In java we have follwing concepts                                                
- Java Colelctions                                                               
-Java Swings                                                                     
-Servlts                                                                         
-JSP               

##############Reverseing cat ##################
[smlcodes@centori ~]$cat a.txt|tac                                               
-JSP                                                                             
-Servlts                                                                         
-Java Swings                                                                     
- Java Colelctions                                     
 In java we have follwing concepts                                                

##############Printing ##################
[smlcodes@centori ~]$cat a.txt|tac|cat                           
-JSP                                                                             
-Servlts                                                                         
-Java Swings                                                                     
- Java Colelctions                                                               
In java we have follwing concepts                         

##############Reverseing cat ##################                       
[smlcodes@centori ~]$cat a.txt|tac|cat|tac                                       
In java we have follwing concepts                                                
- Java Colelctions                                                               
-Java Swings                                                                     
-Servlts                                                                         
-JSP                                                                             
[smlcodes@centori ~]$

2.-cut” inside Pipes

‘cut’ command is used for selecting a specific column of a file.The coulmns can be separated by a demiter like ‘ ’, ‘-’ , ‘,’(space, dash, comma) etc.

Syntax: (here column number staers from 1,2,3…)
cut -d(delimiter) -f(columnNumber) <fileName>

cut -d ' ' -f2 cri.txt
[smlcodes@centori ~]$cat cri.txt 
sachin-350
Gunguly-301
Yuvraj-267
Dravid-321
Dhoni-284

3.”grep” command

grep, which stands for “global regular expression print,” processes text line by line and prints any lines which match a specified pattern.

grep syntax

grep [OPTIONS] PATTERN [FILE...]

Example: Check 3 in cri.txt file

grep 3 cri.txt

$E:\Users\satyacodes\Pictures\12.png$

You can give above example in a single command by using pipe as below

$cat cri.txt |grep 3 cri.txt

grep Options

grep -v: The ‘grep -v’ command displays lines not matching to the specified word.

[satya@centori ~]$cat cri.txt |grep -v 3 cri.txt

Yuvraj-267

Dhoni-284

grep -i: command filters output in a case-insensitive way.

$E:\Users\satyacodes\Pictures\12.png$

4. -comm” command

The ‘comm’ command compares two files or streams. By default, ‘comm’ will always display three columns. Both the files has to be in sorted order for ‘comm’ command to be executed.

First column indicates non-matching items of first file
second column indicates non-matching items of second file
third column indicates matching items of both the files.

5.”tee” Command

The ‘tee’ command is similar to ‘cat’ command with only one difference. It puts stdin on stdout and also put them into a file.

Syntax:

cat or tac <fileName> | tee <newFile> |  cat or tac |.....

$E:\Users\satyacodes\Pictures\12.png$

Here tee.txt is newly created file.

6. -tr” command

The command ‘tr’ stands for ‘translate’. It is used to translate, like from lowercase to uppercase and vice versa or new lines into spaces

Syntax

command | tr <'old'> <'new'>

7.”uniq” command

With the help of uniq command you can form a sorted list in which every word will occur only once

Syntax:

command <fileName> | uniq

$E:\Users\satyacodes\Pictures\12.png$

uniq –c : command will counts the number of occurences of a word. $E:\Users\satyacodes\Pictures\12.png$

8. -wc” (Word Count) Command

wc, or “word count,” prints a count of newlines, words, and bytes for each input file.

Wc –l : for line counts
Wc –w : for word counts
Wc –c : for character counts

$E:\Users\satyacodes\Pictures\12.png$

9. -od” (Octal dump) command

The ‘od’ term stands for octal dump. It displays content of a file in different human-readable formats like hexadecimal, octal and ASCII characters.

Syntax:

od -b <fileName> (display files in octal format)
od -t x1 <fileName> (display files in hexadecimal bytes format)
od -c <fileName> (display files in ASCII (backslashed) character format)

$E:\Users\satyacodes\Pictures\12.png$

10. -sort” command

The ‘sort’ command sorts the file content in an alphabetical order.

**sort -k :** column number is used to sort a specific column

**sort –n -k:** Numarical Sorting with column

$E:\Users\satyacodes\Pictures\12.png$

11. -gzip” command

Gzip (GNU zip) is a compressing tool, which is used to truncate the file size. By default original file will be replaced by the compressed file ending with extension (.gz).

gzip <file1> <file2> <file3>. . . 
gunzip <file1> <file2> <file3>. . .

6.Linux I/O Redirection

Sometimes we need output of a command result as input for another command.

Ex:
cat cri.txt |grep -v 3 cri.txt

This type of operations are known as I/O redirection.We can perform I/O redirect to a File or a Program (to another command)

I/O redirect to a File

We can use Single bracket ‘>‘(overwrite) or double bracket ‘»‘ (append) can be used to redirect standard output

Ovewrite (<):
Commands with a single bracket ’>’ overwrite existing file content.

> : standard output
< : standard input
2> : standard error

Note: Writing ‘1>’ or ’>’ **and **‘0<’ or ’<’ is same thing. But for stderr you have to write ‘2>’.

$E:\Users\satyacodes\Pictures\12.png$

Append(«)
Commands with a double bracket **’»’ do not overwrite **the existing file content.

» - standard output
« - standard input
2»- standard error

$E:\Users\satyacodes\Pictures\12.png$

I/O Redirect to a Program

Pipe ’|’ redirects a stream from one program to another. When pipe is used to send standard output of one program to another program, first program’s data will not be displayed on the terminal, only the second program’s data will be displayed

ls *.txt | cat > txtFile

I/O Redirection Types

The bash shell has three standard streams in I/O redirection:

Standard input (stdin) : The stdin stream is numbered as stdin (0). The bash shell takes input from stdin. By default, keyboard is used as input.
Standard output (stdout) : The stdout stream is numbered as stdout (1). The bash shell sends output to stdout. Output goes to display.
Standard error (stderr) : The stderr stream is numbered as stderr (2). The bash shell sends error message to stderr. Error message goes to display

1. Input Redirection

In input redirection, a file is made input to the command with the help of ‘<’ sign.

**Syntax: To give as input to comamnd**

cat < <filename>

Here we are giving 123.txt file as input to cat comamnd

$E:\Users\satyacodes\Pictures\12.png$

2. Output Redirection

Output redirection is used to put output of one command into a file or into another command.

echo Hello Smlcodes. > sml.txt

3. Error Redirection

Command ‘2>’ redirects the error of an output.It helps us you to keep our display less messy by redirecting error messages.

zcho hyii 2> /dev/null

7.Linux UNIX Tools

Basic UNIX tools are used to do basic work like find a file, locate a file, set the date and time, display calender, etc. There are a number of basic UNIX tools. Some of them are listed below

1.”find” command

The find command help us to find a particular file wihtin a directory and also used to find a list of files having same pattern name.

we may use following symbols in find command

(.) : For current directory name

(/) : For root

find . -name  	: Finding by Name
find . –type	: Find by type
find . –newer	: Finding Newer Files

Example:

[smlcodes@centori ~]$ls                                                          
123.txt  abc.txt  c.zip  javanotes  javaprogs  tik.jpg  users  xxx.zip

####1: all the files ending with '.txt' by name
 [smlcodes@centori ~]$find . -name "*.txt"                                        
./.magic_string.txt                                                              
./123.txt                                                                        
./abc.txt    

###2 : displays all the directories start with 'java’.                                                                 
[smlcodes@centori ~]$find . -type d -name "java*"                                
./javaprogs                                                                      
./javanotes                                                                      
[smlcodes@centori ~]$                                                            

########### Here Options f: regular file
d: directory,	l:symbolic links, c: character devices, b: block devices

2.”locate” command

The locate command finds files by name. locate reads one or more databases prepared by updatedb and writes file names matching at least one of the PATTERNs to standard output.

locate command is a background process and searches the file in database whereas, find command searches in filesystem

locate syntax
locate [OPTION]... PATTERN...

Example:
locate sys.conf

3.”date” command

The date command is used to print out, or change the value of, the system’s time and date information.

date syntax:
date [OPTION]... [+FORMAT]

Example:
[smlcodes@centori ~]$date                                                    
Wed Aug  2 12:40:01 CEST 2017                                                    
[smlcodes@centori ~]$date +'%A %d-%m-%y'                                     
Wednesday 02-08-17

4. -cal” command

cal displays current month’s calender with current day highlighted. We can also display past or future year’s month with cal command.

Syntax:

cal [options] [[[day] month] year]

$E:\Users\satyacodes\Pictures\12.png$

5.-sleep” command

sleep command let the terminal wait by the specified amount of time. By default it takes time in seconds

sleep syntax
sleep NUMBER[SUFFIX]

SUFFIX may be “s” for seconds (the default), “m” for minutes, “h” for hours, or “d” for days.

In above screen, terminal will sleep for 15 seconds

6.”time” command

Report how long it took for a command to execute.

time [-p] command [arguments...]

Example: Check how much time it will take to excecute time command

7.”df” command

The ‘df’ command tells about the disk space used in the file system. It defines the number of blocks used, number of blocks available and the directory where file system is mounte

8.Linux RegEx

Regular expression(regex) is a pattern for a matching string that follows some pattern.Regex can be used in a variety of programs like grep, sed, vi, bash, rename and many more

Metacharacters

A regular expression may have one or several repeating metacharacters.

Metacharacter	Description
.	Replaces any character.
^	Matches start of string and represents characters not in the string.
$	Matches end of string.
*****	Matches zero or more times the preceding character.
**	Represents the group of characters.
()	Groups regular expressions.
?	Matches exactly one character.
+	Matches one or more times the preceding character.
{N}	Preceding character is matched exactly N times.
{N,}	Preceding character is matched exactly N times or more.
{N,M}	Preceding character is matched exactly N times, but not more than N times.
-	Represents the range.
b	Matches empty string at the edge of a word.
B	Matches empty string if it is not at the edge of a word.
<	Matches empty string at the beginning of a word.
>	Matches empty string at the end of a word.

Regex Versions

There are three versions of regular expressions syntax:

BRE : Basic Regular Expressions
ERE : Extended Regular Expressions
PRCE: Perl Regular Expressions

Depending on tool or programs, one or more of these versions can be used.

Examples

[smlcodes@centori ~]$cat ex.txt                                                  
my name is satya kaveti                                                          
come,coming,came                                                                 
going,go, gone                                                                   
sleeping,sleep,slept 

1. Beginning of a line with ‘^a’
[smlcodes@centori ~]$grep ^c ex.txt                                              
come,coming,came

2. End of a line with ‘e$’
[smlcodes@centori ~]$grep e$ ex.txt                                              
come,coming,came
going,go, gone

3. Matching any single character with ‘.a’
[smlcodes@centori ~]$grep .a ex.txt                                              
my name is satya kaveti
come,coming,came

4. Bracket notation with []

This can be a little tricky, brackets allow us to specify characters found within the bracket.
d[iou]g
would match: dig, dog, dug
The previous anchor tag \^ when used in a bracket means anything except the characters within the bracket.
d[\^i]g
would match: dog and dug but not dig
Brackets can also use ranges to increase the amount of characters you want to use.

d[a-c]g
will match patterns like dag, dbg, and dcg
Be careful though as brackets are case sensitive:
d[A-C]g
will match dAg, dBg and dCg but not dag, dbg and dcg

9.Linux Users

1.User information commands (Run for output)

1. whoami : It tells you about the system's username.
[smlcodes@centori ~]$whoami                                                      
smlcodes  

2.who : command gives the users currtely logged users information
[smlcodes@centori ~]$who                                                      
smlcodes  

3. who am i : This command displays the information about the current user only.
[smlcodes@centori ~]$who am i                                                   
smlcodes  

4. ‘w’ : This command tells about the users who are logged in and what are they doing.
[smlcodes@centori ~]$w                                                           
 15:06:07 up 90 days, 20:22,  0 users,  load average: 0.01, 0.05, 0.05           
USER     TTY      FROM 

5. id :  command tells about your user id, primary group id, and a list of groups that belongs to you.
[smlcodes@centori ~]$id                                                          
uid=79458(smlcodes) gid=79459(smlcodes) groups=79459(smlcodes) context=guest_u:gu	est_r:guest_t:s0

2. -su” (Switch User) Command

Su used to Change the current user ID to that of the superuser, or another user.

su syntax

su [options] [username]

Example:

su – hope

Switch the current user ID to that of user hope, and set the environment to hope’s login environment.

The su command, which is short for substitute user or switch user, is used to become another user during a login session.

The root user can become any existing user without knowing that user’s password. Otherwise, password is needed
If any user name is not mentioned then by default, it will assume root as the target user

3. User management commands

User management includes everything from creating a user to deleting a user on your system. The root user is the superuser and have all the powers for creating a user, deleting a user and can even login with the other user’s account. The root user always has userid 0.

The local user database in Linux is /etc/passwd directory.

[smlcodes@centori ~]$tail -5 /etc/passwd                                          
monoidlamba:x:80111:80112::/home/monoidlamba:                                     
bsanchezmu:x:80112:80113::/home/bsanchezmu:                                       
Amitbhawsar:x:80113:80114::/home/Amitbhawsar:                                     
jayanthi123:x:80114:80115::/home/jayanthi123:                                     
moni31:x:80115:80116::/home/moni31:

1.useradd (adding user)

With useradd commands you can add a user.

Syntax:
useradd -m -d /home/<userName> -c "<userName>" <userName>  

Example:
useradd -m -d /home/xyz -c "xyz" xyz

2. usermod (modifying user)

The command usermod is used to modify the properties of an existing user.

Syntax:
usermod -c <'newName'> <oldName>  


Example:
usermod -c 'jhonny' john

3. userdel (Deleting user)

The userdel -r command deletes a user account and all associated files.

Syntax:
userdel -r <userName>  


Example:
userdel -r john

4. passwd

The passwd command is used to change the password of a user account. A normal user can run passwd to change their own password, and a system administrator (the superuser) can use passwd to change another user’s password, or define how that account’s password can be used or changed.

passwd syntax

>   passwd [ OPTION ] [*USER*]

Example: Change Your Password

>   passwd

Running passwd with no options will change the password of the account running the command. You will first be prompted to enter the account’s current password:

4. Group management commands

Users can be listed in different groups. Group allow us to set permission on the group level instead of setting the permission on individual level.

Group File:The /etc/group file defines the group membership. A user can be a member of more than one group.

[smlcodes@centori ~]$tail -5 /etc/group                                           
monoidlamba:x:80112:
bsanchezmu:x:80113:
Amitbhawsar:x:80114:
jayanthi123:x:80115:
moni31:x:80116:

1. groupadd

The groupadd command creates a new group account using the values specified on the command line plus the default values from the system.

groupadd syntax

groupadd [options]

Example: would create a new group called “homegroup”.

groupadd homegroup

2. groupmod

The groupmod command modifies the definition of the specified GROUP

groupmod syntax

groupmod [options] GROUP

example : change the group “homegroup” to “familygroup”

groupmod -n familygroup homegroup

3.gruopdel

The command groupdel will delete a group permanently from the system.

Syntax:

groupdel ****

Example:

groupdel familygroup

10.Linux Permissions

Every Linux system have three types of owners

User: A user is the one who created the file. By default, whosoever, creates the file becomes the owner of the file. A user can create, delete, or modify the file.
Group: A group can contain multiple users. All the users belonging to a group have same access permission for a file.
Other: Any one who has access to the file other than user and group comes in the category of** other**. Other has neither created the file nor is a group member.

Users and groups can be locally managed in /etc/psswd or /etc/group.

To check perimissions of files , use ls –lh command

In above output we have r,w,x. following table explains what they are

permission	Value	on a file	on a directory
r (read)	4	read file content (cat)	read directory content (ls)
w (write)	2	change file content (vi)	create file in directory (touch)
x (execute)	1	execute the file	enter the directory (cd)

File permissions order is like (-rwx-rwx-rwx), for example drwxrwxr-x.

1st Position(d) : denotes file type
1st rwx : user permissions
2nd rwx : group permissions
3rd rwx : other permissions

1.chmod (Chanfe mode) command

chmod is used to set/ change the permissions of files or directories.

Syntax:

chmod [options] <permissions>  <filename>

Exampels:

Exampels:
1. Set permissions of file.htm to "owner can read and write; group can read only; others can read only".
chmod 644 file.htm

2.To add permissions to a group.
Syntax	: chmod <groupName>+<permissionName> <fileName>  
Example:chmod u+x file  

3. To remove permissions from a group
Syntax: chmod <groupName>-<permissionName> <fileName>  
Example:	chmod g-x file   

4. To add permission to all the groups together
Syntax: chmod a+<permissionName> <fileName>  
Example:	chmod a+w file  

5.To add permission to all the groups without typing a
Syntax :	chmod +<permissionName> <fileName>  
Example	:	chmod +w file

2. Unmask

Every file that is created comes with a default set of permissions. If you ever wanted to change that default set of permissions, you can do so with the umask command

$ umask 021

In the above example, we are setting the default permissions of new files to021

3. Sticky Bit

Files can be protected in a directory from being removed by other users who do not own it by preventing it with sticky bit. It is displayed at the same location as the x permission for others

It is represented by a t (x is also there) or a T (no x is there). Generally, sticky bit is found on /tmp directory.

Example:

chmod +t hello.java

11.Linux commands

We have two types of commands in shell.

Built-in commands are internal commands that are built-in the shell. Built-in commands are called from the shell and executed directly within the shell itself. example of built-in commands are ‘pwd’, ‘help’, ‘type’, ‘set’, ‘unset’, etc.
External commands are other than built-in commands. These commands are programs which have their own binary and located in the filesystem Mostly these commands reside in /bin, /sbin, /usr/sbin

1.”type” command

We can check the commands which are belongs to which type by -type” command

[smlcodes@centori ~]$type date                                                    
date is /bin/date                                                                 
[smlcodes@centori ~]$type pwd                                                     
pwd is a shell builtin                                                            
[smlcodes@centori ~]$

2. -alias” command

Sometimes typing commands can get really repetitive, or if you need to type a long command many times, it’s best to have an alias you can use for that. To create an alias for a command you simply specify an alias name and set it to the command.

$ alias foobar=’ls -la’

Now instead of typing ls -la, you can type foobar.Keep in mind that this command won’t save your alias after reboot, so you’ll need to add a permanent alias in:

~/.bashrc

You can remove aliases with the unalias command:

$ unalias foobar

3 .”env” command

-env” outputs a whole lot of information about the environment variables you currently have set.

$env

12.Linux networking

1. TCP/IP Internet protocol

TCP/IP is a set of protocols, and is the primary tech of the internet. When you browse the web, send email, chat online, online gaming, TCP/IP is working busily underneath

Example:

Suppose you are sending email, or downloading a file, or chat with a friend online, or visiting a web page. What happens underneath?

You application (email, chat, etc) breaks the data into thousands of tiny independent pieces. Each piece is called a Datagram (aka packet). Each datagram has embedded with it the destination IP address. Your computer send this datagram to your Router (aka -link”), and your router send it to a appropriate node (another router or computer) on the network that’s closer to the destination.

That router again send it to a another node (router) on the network that’s closer to the destination. This process continues until the designated machine with the IP address receives it. This is done for each and every datagram.

On the receiving machine, it re-assembles all these datagrams into the original whole piece in the right order, and send it to the right application on that machine (the email server, or web server, or chat server. (which in turn, repeat the same thing to send it to your friend’s machine.))

Computer/software follow a set of standardized rules of procedure when talking to each other. This standardized rules of procedure used for internet is called the TCP/IP Internet protocol suite.

2.Network Components

1. Network Interface Controller

First, you have Network interface controller (NIC) (i.e. network interface card, network adapter, LAN adapter, network card). It’s a piece of hardware that lets your computer talk to the internet.

2. Router

Then, the second most important hardware is Router. Router transfer packets between computers.

$E:\Users\satyacodes\Pictures\12.png$

3.MAC Address = Hardware Address = Physical Address

Each Network Adapter has a ID, called MAC address (aka hardware address, physical address). This ID is burned into the hardware. (-MAC” is abbreviation for -Media Access Control” (the name is historical).)

MAC address is a 48 bits number. Usually written as 6 groups of 2 hex digits. For example, 01-23-45-67-89-abor 01:23:45:67:89:ab. Each 2 hex is a octet.

We can find the MAC address of the Network Adapters by using

ip link

ifconfig -a.

[smlcodes@centori ~]$ifconfig -a                                                  
Warning: cannot open /proc/net/dev (Permission denied). Limited output.
Warning: cannot open /proc/net/dev (Permission denied). Limited output.
eth0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
    inet 217.182.92.164  netmask 255.255.255.255  broadcast 217.182.92.164
    ether fa:16:3e:20:dc:3c  txqueuelen 1000  (Ethernet)                                                                                  
Warning: cannot open /proc/net/dev (Permission denied). Limited output.
lo: flags=73<UP,LOOPBACK,RUNNING>  mtu 65536
    inet 127.0.0.1  netmask 255.0.0.0
    loop  txqueuelen 0  (Local Loopback)

4. IP Address

IP address is used to identify all internet devices. (Each internet device may have one ore more IP address.) It’s part of the IP protocol. There are 2 versions of IP address: IPv4 and IPv6.

IPv4 address = 32 bits (4 octets). Usually written in 4 groups, each as a decimal. For example, 172.16.254.1 (for IPv4), each decimal group is 1 octet.
IPv6 address = 128 bits (16 octets). Usually written in 8 groups, 4 digits of hex per group, separated by colon, with leading 0 omitted, for example, 2001:db8:00:567:8:1. Each group of hex represents 2 octets.

IPv4 is the older standard. Because it’s only 32 bits, good for 2\^32 unique address (about 4.2 billion). This is not enough since late 1990s. So, IPv6 was invented.

to find the IP address any router use : ip route.

5. Host, Hostname

A -host” typically refers to a particular computer (or internet device). A Hostname is basically just a name for a machine. It is used mostly as a human-friendly form to identify a machine.

A host/machine may have more than one IP address (because it can have multiple Network Adapter, or, a computer can be setup to function as a router, etc.).

to find your hostname use : hostname

6.Port Number

port → a integer number. It serves as a address for software application to talk to TCP. IP address is used to identify a computer. Once the packet arrived on the computer, the port number serves as a address to identify the software that send/receive messages

7. Network socket

Network Socket is basically a API for programs to talk to the network. A socket address is a combination of IP address and a port number.

So, when a browser, or email app, want to talk to the internet, they speak to the socket. The socket is usually provided by the Operating System as a API. The programer don’t have to worry about TCP/IP details, he just create a socket (by calling a function or new object), specify IP address, port number, and type of connection, and call functions/methods to send/receive data on it.

8. Routing

Routing is one of the most important element in internet, because it is routing that moves data.

By definition, a router has 2 or more network adapters, because a router is used to forward data between different networks. For home routers, usually one end is connected to a cable modem or DSL modem to the internet, and the other hand are Ethernet ports for the home network.

receive data from one of its attached networks.
check the destination address in the IP header. If it’s on the network from whence the data came, the datagram is ignored. (because already reached its destination. (Ethernet sends it to all in the same network))
If destination IP address for a different network, the router checks the routing table to determine where to forward the datagram.
it dis-assemble and re-assemble the datagram and send it to the right adapter.

9. Routing Table

Routing table, or Routing Information Base (RIB), is a data table stored in a router or a computer that lists the routes to particular network destinations, and in some cases, metrics (distances) associated with those routes. The routing table contains information about the topology of the network immediately around it.

To see the routing table your my computer use : ip route or route

[satya@centori ~]$ip route

default via 217.182.88.1 dev eth0 proto static metric 100

217.182.88.1 dev eth0 proto static scope link metric 100

217.182.92.164 dev eth0 proto kernel scope link src 217.182.92.164 metric 100

3.Linux Neworking Commands

1.ifconfig

ifconfig stands for “interface configuration”. It is used to view and change the configuration of the network interfaces on your system.

[smlcodes@centori ~]$ifconfig                                                     
Warning: cannot open /proc/net/dev (Permission denied). Limited output.           
Warning: cannot open /proc/net/dev (Permission denied). Limited output.           
eth0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500                        
        inet 217.182.92.164  netmask 255.255.255.255  broadcast 217.182.92.164    
        ether fa:16:3e:20:dc:3c  txqueuelen 1000  (Ethernet)                    
                                                                                  
Warning: cannot open /proc/net/dev (Permission denied). Limited output.           
lo: flags=73<UP,LOOPBACK,RUNNING>  mtu 65536                                      
        inet 127.0.0.1  netmask 255.0.0.0                                         
        loop  txqueuelen 0  (Local Loopback)

Here, eth0, lo and wlan0 are the names of the active network interfaces on the system.

eth0 is the first ethernet interface. (Additional ethernet interfaces would be named eth1, eth2, etc.) This type of interface is usually a NIC connected to the network by a category 5 cable.
lo is the loopback interface. This is a special network interface that the system uses to communicate with itself.
wlan0 is the name of the first wireless network interface on the system. Additional wireless interfaces would be named wlan1, wlan2, etc

2. PING Command

PING (Packet INternet Groper) command is the best way to test connectivity between two nodes. Whether it is Local Area Network (LAN) or Wide Area Network (WAN). Ping use ICMP (Internet Control Message Protocol) to communicate to other devices. You can ping host name of ip address using below command.

syyntax:

ping

Example:

ping satya.com

3. TRACEROUTE Command

traceroute is a network troubleshooting utility which shows number of hops taken to reach destination also determine packets traveling path. Below we are tracing route to global DNS server IP Address and able to reach destination also shows path of that packet is traveling.

Syntax:

traceroute ****

Exmaple:

traceroute satya.com

4. NETSTAT Command

Netstat (Network Statistic) command display connection info, routing table information etc. To displays routing table information use option as -r.

Syntax:

netstat

5. DIG Command

Dig (domain information groper) query DNS related information like A Record, CNAME, MX Record etc. This command mainly use to troubleshoot DNS related query.

Syntax:

dig

6. NSLOOKUP Command

nslookup command also use to find out DNS related query. The following examples shows A Record (IP Address) of satya.com.

Syntax:

nslookup

Example:

nslookup satya.com

7. ROUTE Command

route command also shows and manipulate ip routing table. In computer networking, a router is a device responsible for forwarding network traffic. When datagrams arrive at a router, the router must determine the best way to route them to their destination.

Route

Route Adding
# route add -net 10.10.10.0/24 gw 192.168.0.1

Route Deleting
# route del -net 10.10.10.0/24 gw 192.168.0.1

Adding default Gateway
# route add default gw 192.168.0.1

8. HOST Command

host command to find name to IP or IP to name in IPv4 or IPv6 and also query DNS records.

Syntax:

host ****

Example

Host satya.com

9. ARP Command

ARP stands for Address Resolution Protocol, will manipulates or displays the kernel’s IPv4 network neighbour cache. It can add entries to the table, delete one, or display the current content.

Syntax:

arp

10. IWCONFIG Command

iwconfig command in Linux is use to configure a wireless network interface. You can see and set the basic Wi-Fi details like SSID channel and encryption

IWCONFIG

11. HOSTNAME Command

hostname is to identify in a network. Execute hostname command to see the hostname of your box. You can set hostname permanently in /etc/sysconfig/network. Need to reboot box once set a proper hostname.

Syntax:

hostname

12. whois

The whois command displays information about a website’s record. You may get all the information about a website regarding its registration and owner’s information.

Syntax:

whois ****

Example:

whois satya.com

13.Linux SysAdmin

A system administrator manages configuration, upkeep and reliable operations of computer operations. Sysadmin handles servers, has to manage system performance and security without exceeding the budget to meet users need.

Some important commands for system administrators

Command	Function
man	Display information about all commands
uptime	Show how long system is running
users	Show username who are currently logged in
service	Call and execute script
pkill	Kill a process
pmap	Memory map of a process
wget	Download file from network
ftp or sftp	Connect remote ftp host
free	Show memory status
top	Display processor activity of system
last	Display user’s activity in the system
ps	Display about processes running on the system
Shutdown commands	Shutdown and reboot system
info	Display information about given command
env	Display environment variable for currently logged-in user
netstat	Display network status
arp	Check ethernet connectivity and IP address
df	Display filesystem information
du	Display usage
init	Allow to change server bootup
nano	A command line editor
nslookup	Check domain name and IP information
shred	Delete a file by over writing its content
cat	Display, copy or combine text files
pwd>	Print path of current working directory
locate	Finding files by name on system
chown	Change ownership of a file
>alias	To short a command
echo	Display text
cmp	Compare two files byte by byte
mount	Mount a filesystem
ifconfig	Display configuration
traceroute>	Trace existing network
sudo	Run a command as a root user
route	List routing table for your server
ping	Check connection by sending packet test packet
find	Find location of files/directories
users	Show current logged in user
who	Same as w but doesn’t show current process
ls	List all the files
tar	Compress directories
grep	Search for a string in a file
su	Switch from one to another user
awk	Search lines for a given pattern

Linux Process Management

Processes are the programs that are running on your machine. They are managed by the kernel and each process has an ID associated with it called the process ID (PID).

1.”ps” command

(ps) Displays information about active processes

ps syntax

ps [options]

Example:

[smlcodes@centori ~]$ps                                                           
  PID TTY          TIME CMD                                                       
10681 pts/27   00:00:00 sh                                                        
10776 pts/27   00:00:00 ps

2.”kill” command

kill is used to send a signal to a process. The default signal for kill is TERM (which will terminate or “kill” the process).

Syntax:

kill -SIGNAL <ProcessId(PID)>

Signal Name	Signal Number	Signal Use
SIGNULL	0	NULL, check access to PID
SIGHUP	1	Hangup
SIGINT	2	Interrupt
SIGQUIT	3	Quit
SIGKILL	9	Kill
SIGTERM	15	Terminate
SIGSTOP	24	Stop

Kill -9 22891

3.service

The service command starts, stop and restart a daemon or services by calling the script. Usually all scripts are stored in /etc/init.d directory.It runs a script in as predictable environment as possible.

Syntax:

service script_name command

Here, command can be anyone from start, stop, restart and status.

**stop command : service script_name stop **
**start command : service script_name start **
**restart command : service script_name restart **
**status command : service script_name status **

VI Editor Usefull commands

References

https://www.javatpoint.com/linux-tutorial

https://linuxjourney.com/

http://www.webminal.org/terminal/

https://www.tecmint.com/linux-network-configuration-and-troubleshooting-commands/

networking : http://xahlee.info/linux/tcp_ip_tutorial.html

http://www.conceptdraw.com/samples/network-diagram

https://www.tecmint.com/linux-network-configuration-and-troubleshooting-commands/