Linux Permissions

Permissions : Read, Write, Execute

r (Read) Permission:

with r permission user can:

• View the content of a file
• List the contents of a directory

w (Write) Permission:

with w permission user can:

• Modify a file
• Create, rename, delete file or dir within a directory

x (Execute) permission:

with x permission user can :

• Execute a file as script
• Can enter in a directory

Permission Category : User, Group, Others

u for User

The files owner

g for Group

The group associated with the file or

o for Others

Everyone Else on the planet.

Interpreting Permission String

When you list files with ls -l, you’ll see something like this:

-rwxr-xr-- 1 alice developers 4096 Apr 4 14:00 script.sh

Let’s dissect it:

• - – Regular file (other values include d for directory, l for symbolic link, etc.)
• rwx – Owner (alice) has read, write, and execute permissions
• r-x – Group (developers) has read and execute permissions
• r-- – Others can only read the file
• 1 – Number of hard links
• alice – Owner
• developers – Group
• 4096 – File size in bytes
• Apr 4 14:00 – Last modification date
• script.sh – File name

File Ownership : User & Group

Files in linux associated with a

• an owner of the file
• a group _By default:
• Who (user) create a file is the owner of the file
• The file is assigned to the primary group of the user (who created the file)

Changing Permissions

Linux has a command for changing permissions & it is chmod.

Symbolic Mode

Uses Symbols (letter & symbols) as permissions & permission Category

Permissions

• r : read
• w : write
• x : Execute

Permission Category

• u : user
• g : group
• o : Others
• a : All

Permission Operator

• + : Add Permission
• - : Remove Permission
• = : Assign Exact Permission

Numeric Mode

This mode uses octal values to represent permission bits:

You sum these for each category:

• 7 = rwx
• 6 = rw-
• 5 = r-x
• 4 = r--

Commands

chmod ugo+rwx filename
chmod 777 filename

Changing Ownership & Group

Using chown & chgrp

Ownership

Changing ownership

chown newuser filename

Group

Changing Group

chgrp newgroup filename 

Ownership & Group

Changing both ownership & group

chown newuser:newgroup filename