Linux chown command

 Linux chown command

This is the most important topic for the security of the files and directories on your Unix/Linux systems. This tutorial covers the file permissions, how to check the current permissions on the file and change them.

To identify the current permissions set on a file or directory. Run ls -l command on terminal. See below image, highlighted section shows the file type and permissions.

There are 10 bits defined with file permissions. Each has a special meaning. Below is the preview of file permissions defined for a file.

Every file on Linux has 3 types of members (owner, group, other) associated with them.

• The first bit shows the file type
• The 2, 3 and 4’th bit shows the permission of the file owner
• The 5, 6 and 7’th bit shows the permission of group members
• The 8, 9 and 10’th bit shows the permission of other users

Type of Roles and Permissions

To understand file permission you must know about Roles and Permission types. There are three types of roles available in Linux systems (User, Group, and Others). Each role has 3 types of permissions (Read, Write, and Execute).

Roles:

• User (Owner)
• Group (All group members)
• Other (All other users

Permissions:

• Read (r) – Member can read the file content or List files in a directory
• Write (w) – Member can write content to file or Create, list, rename, delete a file in a directory
• Execute (x) –< Member can execute any file like sheel script or enter to the directory, and access files and directories

Ways to Change File Permissions in Linux

The chmod command allows users two ways to set permission on any file. Read below about both options:

Symbolic Notation

The symbolic notation used to set permission with alphabets as follows:

Roles:

• u – User
• g – Group
• o – Other

Permissions:

• r – read permission
• w – write permission
• x – execute permission

Octal Notation

The octal notation allows users to set permission in number of formats. Each permission have the pre-defined number as follows

• Read (r) – 4
• Write (w) – 2
• Execute (x) – 1

Possible combinations as follows:

7 - 4+2+1  (rwx)  (Read + Write + Execute)
6 - 4+2    (rw-)  (Read + Write)
5 - 4+1    (r-x)  (Read + Execute)
4 - 4      (r--)  (Read)
3 - 2+1    (-wx)  (Write + Execute)
2 - 2      (-w-)  (Write)
1 - 1      (--x)  (Execute)
0 - 0      (---)  (None)

Linux chown command is used for changing the owner or group owner of a file or directory.

Syntax:

chown <USER>[:<GROUP>] [FILE]...

Example:

Set the file owner of testfile.txt to user “rahul”.

chown rahul testfile.txt

Set the file owner of testfile.txt to user “rahul” and also set the group owner to “root”.

chown rahul:root testfile.txt

Change File Ownership Recursively

You can specify the option -R to change owner and group recursively to all files in the specified directory an subdirectory. For example, set Apache user permission to all files under /var/www/html directory.

chown -R www-data:www-data /var/www/data