Special permissions

The permissions or mode of a file you we will be familiar with is Read, Write, and eXecute (RWX). These permissions can be set to the three objects:

• User
• Group
• Others

The standard permissions are shown with their octal notation, should you want a quick revision exercise, as follows:

There is a fourth block of permissions that precedes user, group, and others. This block is for the special permissions; however, rather than representing RWX, the permissions comprise of:

• The set user ID (SUID) bit
• The set group ID (SGID) bit
• The sticky bit

Using symbolic notations, these permissions can be added to file1, which acts as our axiom for the filename during the following demonstration:

$ chmod u+s file1 #adding the SUID Bit
$ chmod g+s file1 #adding the SGID Bit
$ chmod o+t file1 #adding the Sticky Bit

The SUID bit

The set user ID bit is used when a program needs to run using another user ID other than the user running the program. When set, the program runs with the permissions of the...