How to give file permissions on directories and regular files on Linux.

Linux is a multi-user operating system & can be accessed by many user.We can provide read ,write & execute permission to a file.There are 2 types of authorization levels.

  • Ownership
  • Permission

Ownership

Unix system have three types of owner:

  • User: Who created the file & a user can create, delete, or modify the file.
  • Group: All the users related to a group have same access permission for a file.
  • Other: Any one who has access to the file other than user and group.Other have not a member of user or group.

Permission

Unix system have three types of permissions:

  • Read (r) : we can only open and read the content of a file. But we can’t do any editing or modification in the file.
  • Write (w) : we can only edit, remove or rename a file.
  • Execute (x): we can run the file.

 

There are 2 type to use the command –

  • Absolute mode
  • Symbolic mode

Absolute(Numeric) Mode

Number Permission Type Symbol                            binary
0 No Permission    —                                   000
1 Execute    –x                                   001
2 Write   -w-                                   010
3 Execute + Write   -wx                                   011
4 Read   r–                                    100
5 Read + Execute   r-x                                    101
6 Read +Write   rw-                                   110
7 Read + Write +Execute   rwx                                  111

 

Symbolic Mode

Operator Description
+ Adds a permission to a file or directory
Removes the permission
= Sets the permission

 

The owners are represented as –

u : user/owner

g: group

o: other

a: All

Syntax:

chmod <groupName>+<permissionName> <fileName>  

Example:

Give permission to execute is added to the user owner group.

chmod u+x file-name 

Remove write & execute permissions from a user & group.

chmod u-w file-name 
&
chmod g-x file-name

Give write permission for all the groups.

chmod a+w file-name
or
chmod +w file-name

Give read & write permission for others.

chmod o=rw file-name

Give permissions for all the three groups.

chmod u=rwx,g=rw,o=r file-name 

Give Full permission to a folder

chmod 777 folder-name

change group-owner

chgrp group_name file-name

 

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