Linux_logo_errorbits.comOctal/Absolute mode Permissions

Are specified by adding them in numeric/digit mode, as they are kept in file’s inode. This way previous permission settings are lost and overwritten by the new ones.

Permissions of a file are stored in inode as bits, and they form a construct of 12 bits as follows:

(3 groups * 3 basic permissions) + 3 special permissions = 12 bits in total

Let’s say we have a file with the following permissions: rs-rSxr–

SUID SGID sticky | r w x | r w x | r w x
1 1 0 |  1 1 0 |  1  1  1 | 1 1 0
22 21 20 | 22 21 20 |  22 21 20 | 22 21 20
4 2  0 |  4 2 0 | 4 2  1 |  4 2 0
   6   |     |     |  

Each permission has a value assigned, to get a clear view, take a look at the tables below:

  • Basic Permissions
Octal value  File permission set  Permission details 
 0  —  no permission
1  –x  execute only
 2  -w-  write only
 3  -wx  write & execute
 4  r–  read only
 5  r-x  read & execute
 6  rw-  read & write
 7  rwx  read, write & execute
  • Special Permissions
Octal value  Special permissions set 
 1  Sticky
 2  SetGUID/SGID
 4  SetUID/SUID

Usually, octal mode is the fastest and easiest way to set permissions on files/folders, for the example above we have to type in  the command line:

chmode -R 6676 /file/location/example.txt

If more guidance is needed or something is missing, fell free to ask.


Useful links:

Most used Linux commands

Linux Directory Map / Structure

Introduction to Linux

Using Help in Linux

Download and install Oracle VirtualBox

How to install CentOS on Oracle VirtualBox