Linux Administrator

Linux runs most servers, clouds and security tools. This roadmap takes you from the shell to running, securing and troubleshooting Linux servers. You only need a computer that can run a virtual machine.

• Install a Linux VM (Debian or Ubuntu)
• Open a terminal and run basic commands
• Plan your study time

• CyberA4U Academy — courses

The shell is your main tool as an admin. Fluency means navigating, piping commands together, and scripting repetitive tasks.

• Navigate the filesystem and use pipes and redirection
• Use grep, find, awk and sed
• Write a simple Bash script

Tools & tech: Linux

Learn it on CyberA4U:Module 3: Command Line Mastery for Security Testing

• GNU Bash Reference Manual

Linux security starts with users, groups and file permissions. Mistakes here cause both outages and breaches.

• Manage users and groups
• Read and set permissions and ownership
• Use sudo safely

Tools & tech: Linux

Learn it on CyberA4U:Module 3: Command Line Mastery for Security Testing

• chmod(1) — Linux manual page
• useradd(8) — Linux manual page

The Filesystem Hierarchy Standard explains where configuration, logs, binaries and user data live.

• Know the purpose of /etc, /var, /usr, /home, /tmp and /opt
• Find configuration and logs quickly
• Understand mounts and disks

Tools & tech: Linux

Learn it on CyberA4U:Module 3: Command Line Mastery for Security Testing

• Filesystem Hierarchy Standard 3.0

Package managers install, update and remove software safely with verified sources.

• Install, update and remove packages with apt
• Understand repositories and signing keys
• Apply security updates

Tools & tech: Linux

Learn it on CyberA4U:Module 3: Command Line Mastery for Security Testing

• Debian Reference — Debian package management

systemd starts and supervises services. You'll manage services, read their logs and write your own unit files.

• Start, stop, enable and inspect services
• Write a simple unit file
• Harden units with sandboxing options

Tools & tech: Linux

• systemd.service(5) — Linux manual page

Admins configure and troubleshoot networking from the command line: addresses, routes, DNS and listening ports.

• Use ip, ss and resolvectl
• Configure a static address
• Find which process listens on a port

Tools & tech: Linux

Learn it on CyberA4U:Module 3: Command Line Mastery for Security Testing

• ip(8) — Linux manual page

Logs explain what happened. journald collects system logs; applications may log to files under /var/log.

• Query logs with journalctl
• Understand log rotation
• Forward logs centrally

Tools & tech: Linux

• journalctl(1) — Linux manual page

cron and systemd timers run scheduled jobs such as backups and reports.

• Write crontab entries
• Use systemd timers
• Log and monitor scheduled jobs

Tools & tech: Linux

• crontab(5) — Linux manual page
• systemd.timer(5) — Linux manual page

SSH is the main way into Linux servers. Key-based login, no root login and limited access protect it.

• Use SSH keys instead of passwords
• Disable root and password login
• Limit who can connect

Tools & tech: Linux

• sshd_config(5) — Linux manual page
• Mozilla — OpenSSH security guidelines

nftables is the modern Linux firewall. A default-deny ruleset with only needed ports open reduces exposure.

• Write a basic nftables ruleset
• Allow only required services
• Persist rules across reboots

Tools & tech: Linux

• nftables wiki

Mandatory access control systems confine services so a compromised process can do less damage.

• Check SELinux or AppArmor status
• Read denials in logs
• Adjust policy safely instead of disabling it

Tools & tech: Linux

• AppArmor
• Red Hat — Using SELinux (RHEL 9)

The CIS Benchmarks provide a detailed, tested hardening baseline for Linux distributions.

• Assess a server against a CIS Benchmark
• Apply appropriate settings
• Document exceptions

Tools & tech: Linux

• CIS Benchmarks

A structured method such as the USE method (utilization, saturation, errors) finds problems faster than guessing.

• Apply a repeatable troubleshooting method
• Check resources systematically
• Record findings

Tools & tech: Linux

• Brendan Gregg — The USE Method

Knowing what "normal" looks like makes problems obvious. Record baseline CPU, memory, disk and network usage.

• Use top, vmstat, iostat and free
• Record a baseline
• Compare against it during incidents

Tools & tech: Linux

• Brendan Gregg — Linux performance

Backups must be automated, encrypted, off-machine and regularly tested by restoring.

• Back up files and configurations
• Encrypt and store backups off the machine
• Test restores

Tools & tech: Linux

• restic documentation

Containers are built on Linux namespaces and cgroups. Understanding them helps you run and secure Docker and Kubernetes.

• Explain namespaces and cgroups
• Run and inspect containers
• Apply basic container security

Tools & tech: Linux

• namespaces(7) — Linux manual page
• cgroups(7) — Linux manual page

Check that you can build, secure and troubleshoot a Linux server on your own.

• Manage users, services and packages
• Harden SSH, firewall and the system
• Diagnose performance and log issues

• CyberA4U CTF Arena — practice challenges

You can now administer Linux servers. Continue with Network Administrator, Container Security, or a certification such as LFCS or RHCSA.

• Keep your VM as a lab
• Choose your next roadmap
• Share a hardening guide

• CyberA4U CTF Arena — practice challenges