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