fork() - Theory

fork() is used create a new child process.
Ø  No arguments
Ø  Process ID of the child process
Ø  After the execution of fork() command both parent & child processes are starting their execution from the next line.

Conditions of  fork()
Ø  fork() > 0 -: not only a child process but also a parent process (Successfully child process created.)
Ø  fork() == 0 -: a child process (Successfully child process created.)
Ø  fork() < 0 -: error in memory allocation (Unsuccessful child process)

Example:

Access permission

1.       chmod

Type		Access permission
		User	Group	Other
Directory	d	rwx	r-x	r--
File	-	r-x	r-x	r--
command		u+(access per.)	g+(access per.)	o+(access per.)

Description	Letter representation	Numerical value
readable	r	4
writable	w	2
executable	x	1

Ø  chmod numericalValue filename.fileFormat >>>Ex: chmod 777 file1.txt
Ø  chmod command+letterRepresentation filename.fileFormat >>>Ex: chmod g+w file1.txt

2.       chwon
Ø  chown -R userName:groupName directoryName -: to set a user from the related group as the owner of related directory
>>>Ex: chown -R daniel:admins dir1

Users and Groups

Ø  groupadd groupName -: to create a group
Ø  useradd -G groupName userName -: to add a user to the related group
Ø  passwd userName  -: set a password to the related user
Ø  usermod -a -G  groupName userName -: to add a existing user to a existing group
Ø  login
press “Enter”
give username and password -: to login as related user
Ø  logout -: logout from the user
Ø  grep groupName /etc/group -: to search a group

Ø  userdel userName  -: to remove a user
Ø  groupdel groupName -: to remove a group

File & directory manipulation

1.  cp – copy files and directories
Ø  cp  file1.fileFormat file2.fileFormat -: to copy file1 contents to file2 in same path

Ø  cp  file1.fileFormat /path/file2.fileFormat -: to copy file1 contents to file2 in different path
Ø  cp  file.fileFormat directoryName -: to copy file into a directory in same path
Ø  cp  file.fileFormat /path/directoryName -: to copy file into a directory in different path
Ø  cp -r  directory1Name directory2Name -: to copy directory1 contents to directory2 in same path
Ø  cp -r  directory1Name /path/directory2Name -: to copy directory1 contents to directory2 in different path

2. mv – move files and directories
Ø  mv  file1.fileFormat file2.fileFormat -: to move file1 contents to file2 in same path
Ø  mv  file1.fileFormat /path/file2.fileFormat -: to move file1 contents to file2 in different path
Ø  mv  file.fileFormat directoryName -: to move file into a directory in same path
Ø  mv  file.fileFormat /path/directoryName -: to move file into a directory in different path
Ø  mv  directory1Name directory2Name -: to move directory1 contents to directory2 in same path
Ø  mv  directory1Name /path/directory2Name -: to move directory1 contents to directory2 in different path

3. rm – remove files and directories
Ø  rm filename.fileFormat -: to remove the file
Ø  rm -r directoryName -: to remove the directory

4. find – find files and directories
Ø  find /path -name filename.fileFormat -: to find the file concerning case-sensitive
Ø  find /path -iname filename.fileFormat -: to find the file concerning case-insensitive
Ø  find . -type d -name directoryname  -: to find the directory
Ø  find . -type f -name filename.fileFormat -: to find the file
Ø  find . -type f -name “ *.fileFormat” -: to find all files in related file format

Text editors

1.       nano
Ø  nano -: to start nano text editor
Ø  ctrl+x -: to exit from nano text editor. Then press “y” & give a name with file format to save the file.

2.       touch
Ø  touch filename.fileFormat -: to create a new text file

3.       more
Ø  more filename.fileFormat -: to view the text file

4.       cat
Ø  cat filename.fileFormat -: to view the text file
Ø  cat -n filename.fileFormat -: to display the content with the line number
Ø  cat *.fileFormat -: to view the all text files’ contents.
Ø  cat >filename.fileFormat
                  press enter
                  type file content
                  press enter
                  ctrl+d -: to create a text file
Ø  cat file1name.fileFormat file2name.fileFormat >filename3.fileFormat  -: concatenate existing 2 files and create new file
Ø  cat filename2.fileFormat >filename1.fileFormat  -: to copy the content of file2 to file1
Ø  cat filename1.fileFormat >>filename2.fileFormat  -: to append the contents from file1 to file2

5.       vi – commands are case sensitive
I.            Command mode
Ø  vi fileName.fileFormat  -: to create a text file.
II.            To switch between 2 modes press “i”.
III.            Insert mode
Ø  Enter the content

Editing Commands
i	Insert at cursor
a	Write after cursor
A	Write at the end of line
ESC	Terminate insert mode
u	Undo last change
U	Undo al changes to the entire line
o	Open a new line
dd 3dd	Delete line Delete 3 lines
D	Delete contents of line after the cursor
C	Delete contents of a line after the cursor and insert new text. Press “Esc” to end insertion.
dw 4dw	Delete word Delete 4 words
cw	Change a word
x	Delete character at the cursor
r	Replace character
R	Overwrite characters from cursor onward
s	Substitute one character under cursor continue to insert
S	Substitute entire line and begin to insert at the beginning of the line
~	Change case of individual character
Commands for moving within a file
k	Move cursor up
j	Move cursor down
h	Move cursor left
I	Move cursor right
Commands for saving and closing the file
Shift+zz	Save the file and quit
:w	Save the file while opened
:q	Quit without saving
:wq	Save the file and quit