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Hectal
Phase 8Advanced9 of 9 in Linux

Linux Internals & Troubleshooting

What happens from power-on to login, the kernel's windows into itself (/proc, /sys), finding the real bottleneck on a slow server, tracing a misbehaving process with strace and lsof, and a playbook for the incidents you'll meet most.

Phases 0–7 taught you to use and run Linux. This phase is about the moments when something is wrong and nobody knows why: the server won't boot, it's slow, a process hangs, a port is 'in use'. You'll learn how Linux works underneath and a calm, repeatable way to find out what's happening.

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5 topics ~37 min 7 code blocks & diagrams
Start with the first topic
1
8.1

The Boot Process, the Kernel & systemd Targets

Firmware → bootloader → kernel → initramfs → systemd → your services. Knowing each stage tells you where to look when a machine doesn't come back after a reboot.

8 min 1 diagram 1 code practice

2
8.2

/proc, /sys & Reading the System Directly

Tools like top, free, and ps read their data from /proc. Knowing where it comes from lets you inspect any process or kernel setting directly, even on minimal containers with no tools installed.

7 min 1 code practice

3
8.3

Why Is the Server Slow? Load, CPU, Memory & Disk

A slow server is short of CPU, memory, disk I/O, or network, or it's waiting on something else. A 60-second checklist of standard commands tells you which, before you guess.

8 min 1 diagram 1 code practice

4
8.4

strace, lsof & Debugging a Misbehaving Process

When logs say nothing, watch what the process actually asks the kernel to do. strace shows its system calls, lsof shows its open files and sockets, and together they explain most 'it just hangs' mysteries.

7 min 1 code practice

5
8.5

The Troubleshooting Playbook: Real Incidents, Step by Step

Five incidents you will meet on real servers, each with the order of checks and the fix: can't SSH in, disk full, service won't start, port already in use, and out-of-memory kills.

7 min 1 code practice