System Administration Fundamentals

Responsibilities of a System Administrator

A system administrator may be responsible for installing operating systems, creating user accounts, managing permissions, installing updates, monitoring systems, configuring networks, maintaining backups, and resolving technical problems.

The primary goal is to keep systems available, secure, reliable, and properly configured.

Operating Systems

An operating system manages the computer's hardware and provides the environment in which applications and services operate.

Common server operating systems include Linux distributions such as Ubuntu, Debian, and Red Hat Enterprise Linux, as well as Microsoft Windows Server.

User Accounts

Each user should normally have an individual account. Accounts allow the operating system to identify users and apply appropriate permissions.

On Linux, the following command displays the currently logged-in user:

The following command displays information about a user's identity and group membership:

File Permissions

Linux permissions determine who can read, modify, or execute files and directories.

File permissions can be viewed with:

IP Addresses

An IP address identifies a device on an IP network. A server may use a static address so other devices can consistently locate it.

Private IPv4 networks commonly use address ranges such as:

An example server address on that network might be:

DNS

The Domain Name System, or DNS, converts names into IP addresses. This allows users and applications to locate systems by name instead of remembering numerical addresses.

A DNS lookup can be performed with:

Testing Connectivity

The ping command can help determine whether another host can be reached across an IP network.

If communication fails, an administrator may investigate the local network configuration, gateway, firewall, routing, DNS, or remote system.

Ports

Network services listen on numbered ports. Ports allow multiple network services to operate on the same IP address.

Services

Examples include web servers, DNS servers, database servers, file servers, and remote administration services.

On many Linux systems using systemd, administrators can check the status of a service with:

A service can be restarted with:

Processes

A process is a running instance of a program. Administrators frequently inspect processes when investigating performance or application problems.

An interactive view of running processes can also be displayed with:

Principle of Least Privilege

Users and applications should receive only the permissions necessary to perform their required tasks.

Administrative privileges should not be used for ordinary work when they are unnecessary.

Updates

Operating systems and applications should receive appropriate security updates. Updates often correct vulnerabilities, software bugs, and reliability problems.

Firewalls

A firewall controls network communication according to a defined set of rules.

Administrators should expose only the network services required for the system's intended purpose.

Authentication

Strong passwords and multifactor authentication should be used when supported. Default passwords should be changed, and unused accounts should be disabled or removed.

Backup Fundamentals

Important systems should have a documented backup strategy. Backups should be performed regularly and stored separately from the primary copy of the data.

A backup is only useful if the information can actually be restored. Administrators should therefore test restoration procedures periodically.

A Simple Troubleshooting Process

1. Identify the reported problem.
2. Determine what changed.
3. Check basic connectivity and system status.
4. Review logs and error messages.
5. Develop a likely cause.
6. Test one change at a time when practical.
7. Verify that the service works correctly.
8. Document the problem and solution.

Useful Linux Commands