Understanding Linux Permission Sets

Understanding Permission Sets

It’s all about control. Who gets to do what? In Linux, every file and directory has a set of permissions assigned to it. The permissions identifies “who can do what”. There are three categories of "who" (owner, group, and world). Each of these ownership types is given or denied three permissions. The three permissions are (read, write, and execute).

Basics 
  Permissions (Read, Write, Execute)
  Ownership (Owner, Group, World)
  Identifying Permissions ls –l
  File Types (Normal, Directory)
  Changing permissions.(Symbolic)
  Group permissions (groupadd, chgrp)
Advanced
  Permissions (SUID, SGID, Sticky bit)
  Ownership (Root, sudo)
  Defaults Permissions
  File Types
  Changing permissions (Octal)
  Managing permissions
  Finding special permissions

Basic Permissions (Read, Write, Execute)

The permissions have slightly different meanings depending on what object they are applied to. The two most common objects are files and directories. Below you can see how the permissions change when applied to a file or directory.

File:FileVSfolder.pdf

Permission Sets provide security to your files and directories so you can either give, or not give, permission to users to read, modify, or run those files and directories. Permission Sets are made up of three triplets, each of which contains three characters. These three characters are "R" meaning read, "W" meaning write, and "X" meaning execute. A dash taking the place of any of those characters in the triplet means that the owner, group, or other user(neither the owner nor included in a group), is denied that certain permission. The first set of triplets dictate the permissions to the files owners(users). The second set of triplets dictate the permissions for the group assigned to the file. The third set of triplets dictate the permissions for everyone else.

There are actually ten positions in a Permission Set. The tenth position is in front of the rest. It tells you the type of file that it is. It can be a dash(regular file), a "b"(block device), a "c"(character device), a "d"(directory), an "l"(link), or many others.