Managing User Accounts
Even if you’re the only actual human being who uses your Linux system, understanding how to manage user accounts is important—even more so if your system hosts multiple users.
User accounts serve a number of purposes on Unix systems. Most prominently, they give the system a way to distinguish between different people who use the system for reasons of identification and security. Each user has a personal account with a separate username and password. As discussed in "File Ownership and Permissions,” later in this chapter, users may set permissions on their files, allowing or restricting access to them by other users. Each file on the system is “owned” by a particular user, who may set the permissions for that file. User accounts are used to authenticate access to the system; only those people with accounts may access the machine. Also, accounts are used to identify users, keep system logs, tag electronic mail messages with the name of the sender, and so forth.
Apart from personal accounts, there are users on the system who provide administrative functions. As we’ve seen, the system administrator uses the root account to perform maintenance—but usually not for personal system use. Such accounts are accessed using the su command, allowing another account to be accessed after logging in through a personal account.
Other accounts on the system may not involve human interaction at all. These accounts are generally used by system daemons , which must access files ...