/sheets
A personal reference for frequently used Linux commands and system administration tasks.
LVM Cheat Sheet
Logical Volume Management: physical volumes, volume groups, and logical volumes - creating each layer, extending a logical volume (the classic RHCSA task), growing the volume group first when needed, and the much riskier, XFS-incompatible process of shrinking one.
SELinux Cheat Sheet
SELinux modes, reading and changing file context with semanage and restorecon (not chcon), booleans, and reading AVC denials - the parts that are a genuine knowledge gap for most people studying for RHCSA, who often just disable SELinux instead of learning it.
Boot Process & GRUB Cheat Sheet
From power-on to a login prompt: systemd targets (the modern equivalent of runlevels), systemctl isolate/get-default/set-default, GRUB2 configuration and regeneration, and the classic rd.break procedure for resetting a lost root password.
Linux Server Running Slow Cheat Sheet
A systematic triage flow for a slow Linux server: load average, then CPU, memory/swap, disk I/O and network, with the commands and thresholds to tell which one is actually the bottleneck.
Process Management Cheat Sheet
Inspect and control Linux processes with ps, top, kill/pkill, nice/renice and /proc: process states, signals, priority, process trees and job control.
GitHub Actions Cheat Sheet
Write and manage GitHub Actions workflows: triggers, jobs, steps, secrets, matrix builds and caching, plus the gh CLI commands for watching, re-running and debugging runs from the terminal.
Networking Diagnostics Cheat Sheet
Diagnose network problems with ss, netstat, ping, traceroute and dig/nslookup: is a port open, is a host reachable, where does the connection stall, and is DNS resolving correctly.
Users & Groups Management Cheat Sheet
Create, modify and delete Linux user accounts and groups, understand root vs. admin vs. ordinary users, switch accounts with su, run admin tasks with sudo, and manage /etc/sudoers - plus password aging with chage and the /etc/passwd, /etc/shadow and /etc/group files behind it all.
Open Source Monitoring Tools Cheat Sheet
Monitor Linux systems with htop, glances and netdata for quick host-level checks, plus how Zabbix and Grafana fit in for fleet-wide monitoring and dashboards.
sed & awk Cheat Sheet
Edit text streams with sed (substitution, deletion, in-place editing, addressing) and process columns with awk (fields, patterns, built-in variables, one-liners).
Log Troubleshooting Cheat Sheet
A practical workflow for troubleshooting with plain-text logs in /var/log: where to look first, tailing and searching fast, correlating logs across services, log rotation and disk-full recovery.
Vim & Neovim Cheat Sheet
Core Vim modal editing commands that work identically in Vim and Neovim, plus what actually differs between the two - config files, LSP support and the plugin ecosystem.
journalctl Cheat Sheet
Read and filter the systemd journal with journalctl: by service, time range, priority and boot, follow logs live, and manage journal disk usage.
Bash Scripting Basics Cheat Sheet
Write practical Bash scripts: variables, quoting, arguments, conditionals, loops, functions, arrays, exit codes and the safety flags every script should start with.
tar & Compression Cheat Sheet
Create, extract and inspect tar archives, combine them with gzip/bzip2/xz compression, and work with zip - with the flags that actually matter day to day.
rsync Cheat Sheet
Sync files and directories locally or over SSH with rsync: core flags, excludes, dry runs, deletion safety, bandwidth limits and backup recipes.
iptables & firewalld Cheat Sheet
Manage Linux firewall rules directly with iptables, or through firewalld's zones on Fedora/RHEL, without locking yourself out.
Package Management (apt/dnf) Cheat Sheet
Install, update, remove and search for packages on Debian/Ubuntu (apt) and RHEL/Fedora (dnf), side by side.
Docker Cheat Sheet
Run, build and manage Docker images and containers, plus volumes, networks, Compose basics and safe cleanup.
SSH Cheat Sheet
Connect, authenticate with keys, configure ~/.ssh/config, transfer files, tunnel ports, and harden sshd safely.
My Selection 100 Essential Linux Commands Cheat Sheet
A curated selection of 100 essential Linux commands for sysadmins and power users, grouped by category with practical examples and safety notes.
Linux File System Hierarchy
A practical reference to the Linux filesystem hierarchy: what each top-level directory is for, virtual filesystems, usr-merge, and troubleshooting full disks.
UFW Firewall Cheat Sheet
Set up UFW on Ubuntu/Debian safely: allow SSH first, set default policies, open web ports, use app profiles and troubleshoot.
Crontab Cheat Sheet
Schedule recurring jobs with cron: crontab syntax, time expressions, special values, logging, MAILTO and safe locking with flock.
find Cheat Sheet
Locate files with find by name, type, size, time, owner and permissions, and combine it with grep to search file content.
grep Cheat Sheet
Search text with grep: recursive, case-insensitive, whole-word, inverse and regex matching, with /etc and log file examples.
cat Cheat Sheet
Practical uses of cat for viewing files, numbering lines, revealing control characters and combining files.
Linux Disk & Filesystem Check
Check disk usage, partitions and mounted filesystems with df, du, lsblk, mount, fdisk and blkid, plus swap usage - which processes eat the most swap, and how to control it.
systemctl Cheat Sheet
Useful systemctl commands for managing Linux services.
Linux User and File Permissions Cheat Sheet
Read ls -l output, understand permission classes and octal modes, use chmod and chown safely, and work with SUID, SGID, sticky bit, umask and ACLs.