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Where to start First steps track · 15 stages →

Tracks 11

First steps 15 stages Users, permissions, and processes 13 stages Packages, services, and logs 13 stages Networking 14 stages Storage 11 stages Bash: text processing and scripts 9 stages Inside the system: resources, kernel, processes 12 stages Web stack 9 stages Server security 10 stages Containers: Docker and compose 11 stages Automation: Git and Ansible 6 stages All tracks · 11 →

Labs 77

Easy 17 Medium 53 Hard 7

Topics

First steps 7 Users, permissions, and processes 6 Packages, services, and logs 7 Networking 9 Storage 8 Bash: text processing and scripts 4 Inside the system: resources, kernel, processes 7 Web stack 7 Server security 7 Containers: Docker and compose 5 Automation: Git and Ansible 3 On two machines 9 All labs · 77 →

Wiki 183

Basic commands bash, cd, man Files and directories touch, basename, find Text and search grep, sed, cat Users and permissions ls, chmod, id Processes ps, vmstat, jobs Services and systemd systemctl, crontab, pg_lsclusters Network ping, ip, ss Storage and file systems df, lsblk, pvs Logs and audit journalctl, tail, cat Boot update-grub, uname, sysctl Packages apt, snap Security sudo, sshd, ufw Automation ansible, ansible-playbook Containers systemctl, docker, docker-compose Command index a–z All of the wiki · 183 →

Tools 14

Security

Password generator MD5, SHA and htpasswd JWT decoder

Data formats

JSON validator YAML ⇄ JSON UUID generator

Text

Character counter Compare texts

Linux and network

chmod permissions cron explained IPv4 subnets

Encoding and conversion

Base64 and URL Unix time Data size units All tools · 14 →

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Tracks

Where to start

First steps

15 stages · From system basics and command input to navigation, files, text, and pipelines.

Start the track

Track map 11 tracks · 123 stages

First steps From system basics and command input to navigation, files, text, and pipelines. 15 stages

Users, permissions, and processes From file permissions and accounts to sudo, groups and processes. 13 stages Packages, services, and logs From packages and systemd services to your own unit, the journal, schedules and log rotation. 13 stages

Storage From space diagnosis and mounting, through preparing a new disk, to logical volumes and data recovery. 11 stages Networking From addresses and routes to ports, filtering, DNS, SSH and multi-host connectivity. 14 stages Bash: text processing and scripts Searching and editing text with grep, sed and awk, your own scripts with arguments and checks, exit codes and scheduled runs with a log and a lock. 9 stages

Inside the system: resources, kernel, processes Load average and the CPU, memory and the OOM killer, process limits and kernel parameters, disk load, strace and /proc, kernel messages, the system boot and time synchronisation — up to triaging a slow server. 12 stages Web stack Sites and reverse proxy on nginx, certificates and HTTPS, PostgreSQL access and restoring from a dump — up to a site and a database on two machines. 9 stages Server security What a server exposes and what it keeps running after an update, password policy and fail2ban, a service with least privilege, AppArmor and auditd — up to getting a new server ready for publication. 10 stages Containers: Docker and compose Image and container, ports, environment and restart, your own Dockerfile, volumes, container networking and a compose stack, memory limits and the user inside a container. 11 stages Automation: Git and Ansible Configuration under git: who changed what, how to get the working version back and update a server from a repository; Ansible: inventory, ad-hoc commands and an idempotent playbook — up to configuring a second machine from the first. 6 stages

All tracks · 11 → ←→ sections · ↑↓ links · Esc to close

Labs

Difficulty

Easy 17
Medium 53
Hard 7

Topics

First steps7
Users, permissions, and processes6
Packages, services, and logs7
Networking9
Storage8
Bash: text processing and scripts4
Inside the system: resources, kernel, processes7
Web stack7
Server security7
Containers: Docker and compose5
Automation: Git and Ansible3
On two machines9

New labs

A service holds up the boot Inside the system: resources, kernel, processes 25 min
The pricing service is down Automation: Git and Ansible 20 min
The clocks of two machines drift apart Inside the system: resources, kernel, processes · two machines 25 min

All labs · 77 → ←→ sections · ↑↓ links · Esc to close

Wiki

Sections 183 articles

Basic commands bash, cd, man
Files and directories touch, basename, find
Text and search grep, sed, cat
Users and permissions ls, chmod, id
Processes ps, vmstat, jobs
Services and systemd systemctl, crontab, pg_lsclusters
Network ping, ip, ss
Storage and file systems df, lsblk, pvs
Logs and audit journalctl, tail, cat
Boot update-grub, uname, sysctl
Packages apt, snap
Security sudo, sshd, ufw
Automation ansible, ansible-playbook
Containers systemctl, docker, docker-compose

Command index 432

a
b
c
d
e
f
g
h
i
j
k
l
m
n
o
p
q
r
s
t
u
v
w
x
y
z

Glossary248
Printable cheat sheets183

All articles · 183 → ←→ sections · ↑↓ links · Esc to close

Tools

Popular

Password generator
YAML ⇄ JSON
UUID generator
Character counter

Security

Password generator
MD5, SHA and htpasswd
JWT decoder

Data formats

JSON validator
YAML ⇄ JSON
UUID generator

Text

Character counter
Compare texts

Linux and network

chmod permissions
cron explained
IPv4 subnets

Encoding and conversion

Base64 and URL
Unix time
Data size units

All tools · 14 → ←→ sections · ↑↓ links · Esc to close

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Wiki/Glossary

file lock

Processes

A kernel mark on an open file: while one process holds it, another cannot get the same lock. It is released when the file is closed or the process ends.

In depth in the articles

In depth in the articles

flock — preventing a second run — the full analysis

Related terms

process
file descriptor

Password generator
JSON validator
YAML ⇄ JSON
Character counter
chmod permissions
cron explained

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