User Management and File Permissions

Linux is a multiuser operating system. It is important therefore to be able to manage users:

• Add a new user
• Modify the properties of that new user (e.g. password aging)
• Crate a new group and add existing users to it
• Create users in bulk
• etc.

File permissions and ownership

Of course, the sole reason for having multiple users is to be able to enforce access control i.e. allowing each user to only a subset of the files which exist on the system. A Linux system administrator should be able to:

• Examine the permissions of an existing file
• Changing permissions
• Understand special permissions (e.g. suid, sticky bit)
• Use extended file attributes (e.g. immutable)
• Understand umask
• Changing the owner and group of a file
• etc.

When allowing multiple users to share the same files, it is sometimes useful to be able to create either hard or symbolic links. This is important e.g. when trying to save space or to simplify paths. A Linux system administrator should be able to:

• Create hard links
• Create symbolic links
• Identify broken symbolic links
• Understand the importance of links e.g. in the lib directory