Chapter Summary

A system administrator is someone who keeps the system useful and convenient for its users. Much of the work you do as the system administrator requires you to log in as root. The root user, called Superuser, has extensive systemwide powers that normal users do not have. Superuser can read from and write to any file and can execute programs that ordinary users are not permitted to execute.

You can bring up the system in single-user mode. In this mode, only the system console is functional. When the system is in single-user mode, you can back up files and use fsck to check the integrity of filesystems before you mount them. The telinit utility brings the system to its normal multiuser state. With the system running in multiuser mode, you can still perform many administration tasks, such as adding users and printers.

The system administrator controls system operation, which includes many tasks: configuring the system; booting up; running init scripts; setting up servers; working in single-user, multiuser, and rescue modes; bringing the system down; and handling system crashes. Red Hat Linux provides many configuration tools, both graphical and textual. Many of these tools are named system-config-*.

The xinetd superserver starts server daemons as needed and can help secure a system by controlling who can use which services. You can also use TCP wrappers to control who can use which system services by editing the hosts.allow and hosts.deny files in the /etc directory. By limiting the portion of the filesystem a user sees, setting up a chroot jail can help control the damage a malicious user can do.

You can set up a DHCP server so you do not have to configure each system on a network manually. This task can entail setting up both static and dynamic IP addresses using DHCP. Whether a system uses NIS, DNS, local files, or a combination (and in what order) as a source of information is determined by /etc/nsswitch.conf. Linux-PAM enables you to maintain fine-grained control over who can access the system, how they can access it, and what they can do.