Working with Binary and Octal Numbering
Objective: Apply your skills in binary and octal numbering to configuring *nix directory and file permissions.
Description: As a security professional, you need to understand different numbering systems. For example, if you work with routers, you might have to create access control lists (ACLs) that filter inbound and outbound network traffic, and most ACLs require understanding binary numbering. Similarly, if you’re hardening a Linux system, your understanding of binary helps you create the correct umask and permissions. Unix uses base-8 (octal) numbering for creating directory and file permissions.
Write the octal equivalents for the following binary numbers: 100, 111, 101, 011, and 010. Binary and Octal Numbering
Write how to express *nix owner permissions of r-x in binary. (Remember that the – symbol means the permission isn’t granted.), What’s the octal representation of the binary number you calculated?, (The range of numbers expressed in octal is 0 to 7. Because *nix has three sets of permissions three sets of 3 binary bits logically represent all possible permissions.),
In binary and octal numbering how do you express granting read write and execute permissions to the owner of a file and no permissions to anyone else? Binary and Octal Numbering,
In binary and octal numbering, how do you express granting read, write, and execute permissions to the owner of a file; read and write permissions to group; and read permission to other?
In Unix a file can be created by using a umask which enables you to modify the default permissions for a file or directory. For example, a directory has the default permission of octal 777. ,If a Unix administrator creates a directory with a umask of octal 020, what effect does this setting have on the directory? Hint: To calculate the solution, you can subtract the octal umask value from the octal default permissions.
The default permission for a file on a Unix system is octal 666. If a file is created with a umask of octal 022, what are the effective permissions? Calculate your results.