Linux-Introduction

Introductory Linux for Beginners

What is Linux?

UNIX is an operating system which is a stable, multi-user, multi-tasking system for servers, desktops and laptops. It has a GUI but require that, is not covered by a graphical program or no windows interface available.

The most popular varieties of UNIX: Sun Solaris, GNU/Linux, and MacOS X. We concern with GNU/Linux (simply Linux)

Three parts of UNIX OS:

Part	Meaning	Role
The kernel	The hub of the OS	Allocate time, memory to programs. Handle the filestore communications. Response to system call.
The shell	A command line interpreter (CLI)	Interpret the commands the user types in and arrange for them to be carried out
The programs	A collection of instuctions	Can be executed by a computer to perform a specific task

Files and Processes:

• File: a collection of data.
• Process: an executing program identified by a unique PID.

The Directory Structure:

• All the files are grouped together
• A hierarchical structure like tree, with the top is root (slash /)

Directory:

Command	Meaning	Using	Note
ls <directory>	List file in a directory	ls	Default: the current directory
ls -a	List all files and directories	ls -a	Even hidden files
mkdir <namedir>	Make a directory	mkdir mydir
cd <new_dir>	Change the current working directory to new directory	cd sub_dir
.	The currend working directory
..	The parent directory
~	The home directory
pwd	Display the path ofthe current directory

Manage files:

Command / Symbol	Meaning	Using	Note
touch file	Create a file	touch myfile
echo <test>	Create a text	echo ‘this is my test’
cp <file1> <file2>	Copy file1 which name is file2	cp myfile newfile
mv <file1> <file2>	Move (or rename) file1 to file2	mv myfile newfile	Rename if same directory
rm <file>	Remove a file	rm myfile
rmdir <directory>	Remove a directory	rm mydirectory
cat <file>	Display the contents of a file on the screen	cat myfile.txt	The file is longer than the size of the window, so it scrolls past making it unreadable
less <file>	Display the contents of file onto the screen a page at a time	less myfile.txt	Scrollable, type [q] to quit
head -[<lines>] <file>	Display the first few lines of a file	head myfile.txt head -5 myfile.txt	Default lines=10
tail -[<lines>] <file>	Display the last few lines of a file	tail myfile.txt tail -5 myfile.txt	Default lines=10
grep <keyword> <file>	File search a file for keywords	grep monday myfile.txt
wc [-c] [-w] [-l] <file>	Count number of lines/words/characters in file	wc myfile.txt wc -c myfile.txt	default: all -c: characters -w: words -l: lines

Redirect the input/output:

Command / Symbol	Meaning	Using	Note
cat	Write the contents of a file to the screen without specifying a file to read	Type a few words on the keyboard and press the [Return] key. Press [Ctrl+D] to end the input
sort	Alphabetically or numerically sort a list		without specifying a file to sort as using of cat
<	Redirect standard input to a file	command < file
>	Redirect standard output from a file	command > file	write over the content of the file
>>	Append standard output to a file	command >> file	write at the end of the content of the file
pipe	Pipe the output of command1 to the input of command2	command1 pipe command2	| is a pipe
cat <file1> <file2> > <file0>	Concatenate file1 and file2 to file0
who	List users currently logged in

Special character to help us managing files:

Command / Symbol	Meaning	Examples	Note
*	Wildcard, match against none or more character(s)
abc*	All files in the current directory starting with abc...	abcss,abct,abcd,abc
*abc	All files in the current directory ending with ...abc	sffabc,fabc,abc
~	Willcard, match exactly one character	~ouse: house, mouse, grouse
man	Read the online manual page for a command
help	Short description of the use of the command		using
whatis	Brief description of a command		meaning
apropos	Match commands with keyword in their man pages

Security system and permissions, process:

Command / Symbol	Meaning	Examples	Note
ls -l	List access rights for all files	#	d: directory r: read permission w: write permission x: execution permission -: no permission
chmod [<options>] <file>	File change access rights for named file	chmod go-rwx mylist to remove,read ,write and execute permissions on the file biglist for the group and others chmod a+rw mylist to read and write permissions on the file biglist to all	u: user g: group o: other a: all r: read w: write (and delete) x: execute (and access directory) +: add permission -: take away permission
ps	See information about your processes	PID TTY TIME CMD 10544 pts/0 00:00:00 bash 11426 pts/0 00:00:00 ps
bg	Show background the suspended job
jobs	List current jobs
fg %jobnumber	Restart(foreground) a suspended progress	fg %1
[Ctrl+C]	Kill the job running in the foreground
[Ctrl+Z]	Suspend the job running in the foreground
kill %jobnumber	Kill job number	kill %2
kill processnumber	Kill process number	kill 26152	PID

Other commands:

Command / Symbol	Meaning	Examples	Note
df	Space left on the system
du	Kilobytes used by a directory
gzip <file>	Compress a file	gzip science.txt -> zipped file: science.txt.gz
gunzip <file>	To expand the file	gunzip science.txt.gz
zcat <file>	Read zipped file without needing to uncompress them first	zcat science.txt.gz
file <directory>	Classifies the file according to its type
diff <file1> <file2>	Compares the contents of two files and displays the differences
history	Keeps an ordered list of all the commands

The download, installation and compilation process of a programme in Linux:

Steps needed to install the software:

• Locate and download the source code (which is usually compressed)
• Unpack the source code
• Compile the code (the most difficult)
• Install the resulting executable
• Set paths to the installation directory

The wy to compile a package:

• cd to the directory containing the package's source code
• Type ./configure to configure the package for your system
• Type make to compile the package
• Optionally, type make check to run any self-tests that come with the package
• Type make install to install the programs and any data files and documentation
• Optionally, type ` make clean to remove the program binaries and object files from the source code directory

Example:

• Download source code: A piece of free software that converts between different units of measurements.
  First create a download directory:
  % mkdir download
  Download the software here and save it to your new download directory.
• Extract source code:
  Go into your download directory and list the contents:
  % cd download
  % ls -l
  First unzip the file using the gunzip command. This will create a .tar file.
  % gunzip units-1.74.tar.gz
  Then extract the contents of the tar file.
  % tar -xvf units-1.74.tar
  Again, list the contents of the download directory, then go to the units-1.74 sub-directory.
  % cd units-1.74
• Configure and create the Makefile:
  The units package uses the GNU configure system to compile the source code. We will need to specify the installation directory, since the default will be the main system area which you will not have write permissions for. We need to create an install directory in your home directory.
  % mkdir ~/units174
  Then run the configure utility setting the installation path to this.
  % ./configure --prefix=$HOME/units174
• Build the package:
  Now you can go ahead and build the package by running the make command.
  % make
  After a minute or two (depending on the speed of the computer), the executables will be created. You can check to see everything compiled successfully by typing
  % make check
  If everything is okay, you can now install the package.
  % make install
  This will install the files into the ~/units174 directory you created earlier.
• Run the software:
  You are now ready to run the software (assuming everything worked).
  % cd ~/units174
  If you list the contents of the units directory, you will see a number of subdirectories (bin,info,man,share)
  To run the program, change to the bin directory and type
  % ./units
  As an example, convert 6 feet to meters.
  You have: 6 feet
  You want: metres
  * 1.8288
  If you get the answer 1.8288, congratulations, it worked.
  To view what units it can convert between, view the data file in the share directory (the list is quite comprehensive).
  To read the full documentation, change into the info directory and type
  % info --file=units.info

UNIX Variables

Standard UNIX variables are split into two categories:

• ENVIRONMENT variables: have a farther reaching significance, and those set at login are valid for the duration of the session
• shell variables: apply only to the current instance of the shell and are used to set short-term working conditions

Some ENVIRONMENT variables:

Variable	Meaning
USER	your login name
HOME	the path name of your home directory
HOST	the name of the computer you are using
ARCH	the architecture of the computer's processor
DISPLAY	the name of the computer screen to display X windows
PRINTER	the default printer to send print jobs
PATH	the directories the shell should search to find a command
OSTYPE	the value of this is the current operating system you are using

Some shell variables:

Variable	Meaning
cwd	your current working directory
home	the path name of your home directory
path	the directories the shell should search to find a command
prompt	the text string used to prompt for interactive commands shell your login shell

References

UNIX Tutorial for Beginners
Erle Robotics Unix Introduction Gitbook

License

Creative Commons Attribution 4.0 International (CC BY 4.0) @ Willogy