rootLinux · Unix · DevOps · Infrastructure
Practical knowledge for people who run servers.
Look up a command. Fix an incident. Prepare for the interview.
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Troubleshoot by symptom
Start with what you see, not what you know.
Start here: pick your path
Ordered reading lists. Ticks appear as you visit pages (stored only in your browser).
🌱 Linux beginner
New to Linux. Build the foundation, one chapter at a time.
🐧 Linux administrator
You run Linux servers. Go deeper on storage, network, security and performance.
🏛️ Senior sysadmin / L3
Enterprise Unix and Linux, clustering, hardware and operations.
♾️ DevOps engineer
Automation, containers and the toolchain around Linux.
🎯 Interview preparation
Practice answering out loud, not just reading.
🚨 On-call & troubleshooting
Something is broken right now.
Explore topics
7 topic hubs · 15 guides · 376+ Q&As · about 142k words, all free.
Linux & RHEL →
RHEL administration, Linux commands, storage, boot, networking and day-to-day troubleshooting.
Unix →
Oracle Solaris and HP-UX: ZFS, Zones, LDOMs, LVM/VxFS, boot and enterprise operations.
Networking →
CCNA study notes and a protocol reference for routing, switching, VPN and troubleshooting.
Infrastructure →
Nutanix HCI and server hardware: iLO, iDRAC, RAID, blades and day-2 operations.
DevOps →
Podman containers, Ansible Automation Platform and a DevOps handbook.
Operations →
ITIL processes mapped to real Unix/Linux operations: incident, problem, change, DR.
Interview preparation
L1 → L2 → L3 questions pulled from every guide, with a random-question and practice mode.
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Start Here
Pick a learning path: Linux beginner, Linux administrator, senior sysadmin, DevOps, interview preparation or on-call troubleshooting.
Linux & Unix Cheat Sheets
Printable Linux command cheat sheets for daily administration: filesystems, LVM, systemd, networking, processes, performance, SELinux, Solaris, Podman, Ansible and Git.
Practice Labs
Scenario-based Linux troubleshooting practice: try the problem first, then reveal a suggested investigation approach.
Why Linux says “Read-only file system” and how to fix it
The kernel remounted a filesystem read-only. Learn how to confirm it, find the cause (I/O errors, ext4/XFS errors, SAN/multipath) and recover safely.
Filesystem 100% full: find what is eating the disk
How to find what filled a Linux filesystem: df and du, deleted-but-open files, inode exhaustion, logs and journal, and safe cleanup steps.
High load average: is it CPU, memory or I/O?
A fast triage for high load average on Linux: read uptime, separate CPU, I/O wait and memory pressure, and find the offending process.
Quick fixes
Short, symptom-first pages: the deeper write-up behind each Reel.
Why Linux says “Read-only file system” and how to fix it
The kernel remounted a filesystem read-only. Learn how to confirm it, find the cause (I/O errors, ext4/XFS errors, SAN/multipath) and recover safely.
Filesystem 100% full: find what is eating the disk
How to find what filled a Linux filesystem: df and du, deleted-but-open files, inode exhaustion, logs and journal, and safe cleanup steps.
High load average: is it CPU, memory or I/O?
A fast triage for high load average on Linux: read uptime, separate CPU, I/O wait and memory pressure, and find the offending process.