File Permissions

 

File Permissions In Linux

• Just like every operating system, Linux comes with a set of permissions that it uses to protect files, directories, and devices on the system.
• These permissions can be manipulated to allow (or) disallow access to files and directories on different parts of the system.

Basic file permissions

Let’s look at how permissions work first. Linux permissions are implemented through the properties of files and are defined by three separate categories.

 

User: The person who owns the file.

Group: The group that owns the file.

Other: All other users on the system.

Permissions in Linux can be assigned one of two ways. You can use the mnemonic or a single digit to represent the permission level.

Operation	Digit	Mnemonic	Description
Read	r	4	View file contents.
Write	w	2	Write to me or change.
Execute	x	1	Run the file.

Default file permissions

Umask: Universal mask is a default value that always gets dedicated from maximum file permission allocated for every file & directory.

For super user umask value is # 022.

For Normal user, the umask value is $002

For superuser:

Maximum permission of a file 666-Umask (-)022

Default file permission ------>  644

Maximum permission of a directory 777-Umask (-)022

Default directory permission 755

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For Normal user:

Maximum permission of a file ---- 666----Umask (-)_002---664

Maximum permission of a directory---777 umask---002 (-)775

To see the umask # umask

To change the umask # umask 222

To view umask value from the fiel # vim /etc/ bashrc

Operators:

+  --->To add a permission.

-  --->To remove permission.

= --->To override the permission.

Here are some of the commands you can use to work with permissions:

Chmod:- It is used to change the permission of a file and directory. It can be used by the owner of the file (or) by root.

Syn: Chmod [options] [permission]   [file]

R ---> Acts recursively.

V ---> Provides verbose output.

Ex:      

1) # Chmod u+rw,g+r, o+x   linux # Chmod 641 linux

2) #chmod ugo =rw backup (or) # chmod 666 backup

3) #chmod U-W, g-r, o-x  linux

4) #chmod-R U+W, g+r, o+x linux

5) #chmod-R 777 unix

6) # chmod 755 Unix

 

Linux Tutorials

 

Chgrp: à By using this command we can change the group of the file.

Syn: Chgrp [options] [group name] [file]

R ---> Recursively

V ---> Verbose

Ex: #ls-l linux #chgrp sales linux

Chown: This command is used so we can change the owner of the file, as well as owner & group at a time.

Syn: Chown [options] [user:group] [file]

R---> Recursively

V---> Verbose.

Ex:      

#Chown Raju Linux                       To Change the only owner.

#Chown Raju: sales Linux             To Change owner & group

#Chown –R Ramu: color Unix     Recursively to change.

To view the symbolic as well as a numeric mode of permission

# stat Linux

To change the permissions in GUI mode

#navtilus &

Assign the permissions in GUI mode:

Right-click on file ----->properties---->permissions.

For an in-depth understanding of Linux click on

• Features of UNIX/LINUX
• Architecture of O/S
• UNIX Introduction
• Basic commands
• User Administration