Chapter 7. File Permissions | HP Certified: HP-UX System Administration

Chapter Syllabus

7.1 Who Are UNIX Users?

7.2 Types of File Permissions

7.3 Modifying File Permissions

7.4 Default File Permissions

7.5 Changing the Owner and Group of a File

7.6 Special File Permissions

7.7 Finding Files Having a Particular Set of File Permissions

7.8 Access Control Lists

7.9 Miscellaneous Commands

In a multiuser operating system like UNIX, many people are using system resources including disks and files. It is important to keep individual user files secure so that other users are not able to read, modify, or delete them. At the same time, users may be working on the same project and need to share files among themselves . It becomes important that a user be able to grant read or write access to some of the other users. If a group of programmers is working on some software development project, they need to share code and information. They also need to protect this information from people outside the group.

UNIX implements a file security policy by dividing users into three categories. These are the owner of a file, the group of users to which the owner of a file belongs, and all other users of the system. Files and directories can be granted read, write, or execute permissions to one or more user groups. In addition to this file permission scheme, HP-UX also implements another scheme, which is known as access control lists (ACLs). Using an ACL, individual users can also be granted specific permissions in addition to group permissions.

In this chapter, we will go through some basic concepts of UNIX file permissions. You will learn categories of UNIX users and how file permissions are managed among them. You will study types of file permissions and how to change them. Here some commands to change or modify file permissions will be introduced. All users can't use all of these commands, and you will see who is permitted to do what. There is a set of default file permissions, and you will see how to deal with it. Many times you need to change the owner or group of a file, and you will learn some commands to do so. You will see what the special file permissions are and how these affect system security. Then there will be a method to find files with a particular set of permissions. In the end, ACLs will be introduced and a method for listing and changing the ACL associated with a file will be presented.

After going through this chapter, you will be able to list and modify file and directory permissions and ACLs. You will also be able to find potential security problems related to wrong file permissions.

Top