Last Updated on 3 years by ICT Byte

Linux Authorization

For security purpose, LINUX divides authorization in

• Ownership
• Permission

Ownwership

• In linux, every file and directory is assigned with 3 tyoes of owner
  • User
    • Owner of the file
    • Who creates a file is owner by default
    • Its owner of the file
  • Group
    • Has multiple users
    • All users in a group has same permission to access the file
    • If you assigned permission to group, no one else can read except group members
  • Other
    • Other users other than users and group
    • Everybody else
    • This user hasn’t created file and doesn’t belong to any group

Permission

• In linux, every file can be assigned with 3 permissions
  • Read
    • Has authority to open and read file
    • Content of directory can be listed
  • Write
    • Access to modify content
    • Adding, removal of content
    • File can be renamed
  • Execute
    • .exe in windows, which can run
    • To run program, execute permission is needed

Examples:

Is –l on linux terminal gives

Here, rwxrwxrwx code tells about the permission that are given owner, group and world

Character means,

r = read

w = write

x = execute

-= no permission

Let us see

rw-

which means for the user in file / folder can

• Read file
• Write or edit the file
• Can’t execute as permission is set –

First part is for user, second for group and third for world.

Changing file/directory permission

• We can use chmod command
• Chmod stands for changemode
• Permission (read, write, execute) can be set with this command
• Syntax: chmod permission filename

Chmod command can be used in two ways

Absolute mode

• Here, permission are represented as three digit octal number

Number	Permission	Symbol
0	No Permission	—
1	Execute	–x
2	Write	-w-
3	Execute + Write	-wx
4	Read	r–
5	Read + Execute	r-x
6	Read +Write	rw-
7	Read + Write +Execute	rwx

• Example : chmod 777 filename
  • 777 represents read write and execute permission for user, groud and others all
• Chmod 707
  • 707 represents user have read write and execute permission, group has no permission and others have read write and execute permission.

Symbolic Mode

• In absolute, we change permission for all 3 owners
• In symbolic, permission can be modified for specific owner
• Mathematical symbol is used

Operator	Description
+	Adds a permission to a file or directory
–	Removes the permission
=	Sets the permission and overrides the permissions set earlier.

Users are represented as

u=user

g=group

o=other

a=all

Example

Chmod o=rwx examplefile

This is setting permission tp others

Chmod g-r test

This is removing read permission for group from file test

Changing ownership and group

• To changeownership, chown command is used
• Chown user

If you want to change the user and group for a file

Chown user:group filename

If you want to change group owner only

Chgroup group-name filename

Chgrp stands for change group