mktemp Command: Creating Safe Temporary Files
Why fixed-name or $$ temp files are dangerous, and how mktemp creates unique, owner-only temporaries that trap cleans up reliably.
Read more →⚡ Tutorials
A collection of hands-on tutorials to learn Linux techniques step by step. From basic commands to advanced skills, each tutorial includes rich examples and detailed explanations.
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🚀 Basic Operations
Beginner
read Command: Interactive Input in Shell Scripts
Learn how the read command captures keyboard input and reads files line by line, explained through Lina and Linny-senpai's dialogue. Covers -p, -s, and while read.
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file Command: Detecting File Types
Extensions can lie. Learn how the file command inspects content to reveal what a file really is, explained through Lina and Linny-senpai's dialogue.
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printf Command
Learn printf with Linny-senpai and Lina. Covers the difference from echo, format specifiers like %s, %d, and %f, width padding, and escape sequences.
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watch Command
Learn with Linny-senpai and Lina! Rerun a command at a fixed interval and monitor how its output changes. Covers -n intervals, -d diff highlighting, quoting pipes, and how to exit.
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wc Command
Learn with Linny-senpai and Lina! Master wc basics (-l lines / -w words / -c bytes / -m characters), the `ls | wc -l` counting pattern, and why bytes and characters differ for multibyte text.
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How to Use pwd, cd, and ls
Learn with Linny-senpai and Lina! Master pwd (location), ls (list), and cd (move) - the 3 essential commands for beginners.
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How to Use mkdir, touch, and echo
Learn with Linny-senpai and Lina! Master mkdir (create directories), touch (create files), and echo/cat (view contents).
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How to Use cp, mv, and rm
Learn basic file operations: creation, editing, copying, moving, and deletion. Includes introduction to text editor basics.
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tree Command: Visualizing Directory Structure
When ls alone makes it hard to grasp a layout, tree visualizes the whole directory structure at once. Learn to limit depth with -L, show folders only with -d, and exclude node_modules with -I.
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Environment Variables Basics - Configuration and Practical Usage
Learn Linux environment variables for beginners. From echo and env to export, PATH, and persistence with .bashrc, taught through Lina and Linny-senpai's dialogue.
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locate, which, and whereis - Three Ways to Find Commands in Linux
Learn the differences between locate, which, and whereis. Solve "where did it install?" and "which python is running?" with the right command for the job.
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md5sum and sha256sum: Verifying File Integrity
Learn with Linny-senpai and Lina! What a hash is, computing one with sha256sum, verifying with -c, the difference between corruption and tampering, and why MD5 is discouraged today.
Read more →🔐 Permissions & Process Management
Intermediate
How to Use chmod and chown
Detailed explanation of file and directory permissions, chmod, chown, umask and other permission-related commands.
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How to Choose Between chmod, chown, and sudo
Practical learning of advanced permission management including special permissions, ACL, and security configuration.
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Fixing Permission Denied at the Root Cause
Detailed explanation of permission configuration best practices and real-world examples used in system administration.
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How to Use ps, top, and kill
Learn process concepts and process management commands including ps, kill, jobs, and nohup.
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Getting Started with Job Control - jobs, fg, bg, and Ctrl+Z
Learn shell job control through Linny-senpai and Lina's dialogue: pause with Ctrl+Z to free your terminal, swap with fg/bg, list with jobs, and run with & — including the kill %1 pitfall — for absolute beginners.
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nohup/disown/screen - Keeping Processes Running After Logout
Three ways to keep processes running after SSH disconnect or terminal close. Learn nohup (before start), disown (after start), and screen (full session reattach), plus when to use each.
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nice and renice Basics - Controlling Process Priority
Control CPU scheduling priority with nice and renice. Covers the nice value range (-20 to 19), setting priority at launch, changing it dynamically for running processes, and root vs user permission rules.
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Linux Process Management in Practice
Learn practical techniques including system monitoring, performance tuning, and troubleshooting.
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fuser: Finding Processes Using Files
Find the culprit behind umount "target is busy" with fuser, then kill it safely. Includes a fuser vs lsof comparison.
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taskset: Setting CPU Affinity in Linux
Pin a process to specific CPU cores with taskset. Launch-time pinning with -c, runtime reassignment with -p, plus benchmarking and core-isolation workflows.
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chroot: Changing the Root Directory to Isolate an Environment
Switch the root directory a process sees with chroot. Covers preparing shared libraries, recovering a broken system from a live USB, and why chroot is not a security boundary.
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User Management Basics: useradd, usermod, and userdel
Learn how to create users with useradd, modify group memberships and attributes with usermod, and delete accounts with userdel. Covers sudo privileges and group management patterns.
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Linux Group Management Basics: groupadd, groupmod, and Access Control
Learn how to create groups with groupadd, modify them with groupmod, and manage members with usermod -aG and gpasswd. Covers /etc/group format, shared directory setup, and sudo privilege patterns.
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Understanding sudo vs su - Safe Privilege Escalation in Linux
Learn the difference between sudo and su, why sudo is the recommended approach, and how to configure sudoers safely with visudo. Covers common mistakes and a practical quick-reference for daily use.
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sudoers Configuration Basics - Delegating Privileges Safely
Learn how to configure /etc/sudoers safely using visudo. Covers syntax, NOPASSWD, per-command delegation, and sudoers.d best practices on Ubuntu.
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Understanding umask - Controlling Default File Permissions
Learn how umask determines default permissions for new files and directories. Covers the AND NOT calculation, common values like 022/077/002, and how to make changes persistent via .bashrc or /etc/profile.
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chown and chgrp Basics - Changing File Ownership in Linux
Learn how to change file owner and group with chown and chgrp. Covers user:group syntax, -R recursive changes, and common web server deployment patterns.
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Understanding SUID, SGID, and Sticky Bit - Special Permission Bits in Linux
Learn how SUID, SGID, and Sticky Bit work in Linux. Understand special permission bits with practical chmod examples and security guidance.
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SELinux Introduction: Your First Step to Reading Denial Logs
Learn SELinux basics — check modes with getenforce, read AVC denial logs, and use ausearch and audit2why to identify what is being blocked and why.
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User and Group Management in Practice - Setting Up Multi-User Environments
A practical guide to managing users and groups with useradd, usermod, and groupadd. Covers multi-user setup and reading /etc/passwd on Linux.
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passwd and chage: Password and Account Aging
Manage passwords and account locking with passwd, and password aging and expiry with chage. Includes how to read /etc/shadow.
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who, w, and last
Who is logged into this server right now? When did they log in? Use who, w, and last to inspect logged-in users, what each one is doing, and past login history. Covers reboot history and failed logins too, explained step by step in a friendly dialogue.
Read more →💪 Advanced Skills
Advanced
How to Use head, tail, and Pipes
Learn advanced file operation techniques including links, compression/decompression, and backup technologies.
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How to Use find, grep, and awk
Practical learning of advanced file search and processing techniques using find, grep, awk. Aimed at professional-level mastery.
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fd: A Simpler Alternative to find
find has complex syntax and is slow. With fd, just type `fd pattern` for a recursive search that respects .gitignore. From the fdfind install gotcha to extensions, types, and exec.
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How to Use find, grep, and awk - Basics
Systematic learning of basic file search and text processing commands.
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grep and awk Advanced Techniques
Learn advanced techniques including complex search conditions, regular expressions, and awk programming.
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How to Combine find, grep, and awk
Detailed explanation of practical use cases and best practices used in real-world work.
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find, grep, and awk Exercises
Detailed learning of professional-level advanced techniques and optimization methods.
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How to Write Shell Scripts
Systematic learning of shell script writing basics, variables, control structures, and functions.
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Shell Scripting in Practice
Learn practical shell script creation methods, debugging techniques, and performance optimization.
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bash Parameter Expansion — Understanding ${var:-x} and Related Syntax
bash parameter expansion cheat sheet covering default values, substring extraction, pattern removal, replacement, and case conversion with practical examples.
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getopts: Parsing Command-Line Options in Bash
Parse command-line options (-a, -b value) robustly in Bash with getopts. Covers optstring, OPTARG, OPTIND, silent-mode error handling, and how getopts differs from getopt.
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trap - Handling Signals and Cleanup in Bash
Use trap to catch signals (Ctrl-C, kill) and run reliable cleanup. Covers the EXIT pseudo-signal, cleanup functions, and combining trap with set -e for robust scripts.
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Heredoc Basics - Embedding Multiline Strings in Shell Scripts
Learn how to use heredoc (<<EOF) to embed multiline strings in shell scripts. Covers variable expansion control, stripping indentation with <<-, writing to files, and practical use cases with SSH and databases.
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Bash Strict Mode: set -euo pipefail Explained
Catch hidden bugs early with set -euo pipefail. Learn errexit, nounset, pipefail, their pitfalls, and IFS settings for safer shell scripts.
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bash History Tips - Making the Most of Your Command History
Learn to reuse bash commands with Ctrl+R search, !!, !$, and history numbers. Covers HISTSIZE and HISTCONTROL settings for efficient shell use.
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journalctl Basics: Log Investigation
Learn how to check logs in Ubuntu (systemd) environments. Master filtering by time, service, and priority level for effective troubleshooting.
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journalctl in Practice - Filtering Logs from the systemd Journal
Master journalctl filtering. Filter logs by unit, time range, priority, and fields to quickly extract exactly what you need from the systemd journal.
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dmesg: Reading Kernel Ring Buffer Messages
Read the kernel ring buffer with dmesg. From permissions, timestamps, and level filters to triaging disk I/O, OOM, and hardware faults.
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sysctl: Tuning Kernel Parameters on Linux
Read, change, and persist Linux kernel parameters with sysctl. Covers runtime changes, /etc/sysctl.d drop-ins, precedence, and verification.
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ulimit: Understanding Resource Limits
Control how many resources a process can use with ulimit. Covers soft vs hard limits, the open files limit, persisting limits via limits.conf and systemd, and diagnosing Too many open files.
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tar Basics: Compression, Extraction & Avoiding Mistakes
Learn tar command for compression, extraction, and listing contents. Understand .tar.gz/.tgz/.tar differences and how to prevent extraction accidents.
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gzip vs bzip2 vs xz vs zstd - Choosing a Compression Format
Compare gzip, bzip2, xz, and zstd on ratio and speed, then choose per use case. Covers tar integration, compression levels, and multithreading.
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zip and unzip Basics
Learn with Lina and Linny-senpai! Cross-platform compression made simple. Zip it up, unzip it open, and fix garbled filenames from Windows archives along the way.
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Pipes and Redirection Basics
A beginner-friendly dialogue tutorial. Learn how `|`, `>`, `>>`, and `2>&1` work by following the flow of stdin, stdout, and stderr — and combine commands with confidence.
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Getting Started with nano - The Beginner-Friendly Editor Before Vim
Learn nano through dialogue with Lina and Linny-senpai! Open, edit, save (Ctrl+O), and exit (Ctrl+X) without memorizing anything — shortcuts are always shown at the bottom of the screen.
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Vim Basics - Essential Commands and Practical Techniques
A practical Vim guide covering modes, motions, edits, search/replace, and save/quit. Stop getting stuck and learn the minimal .vimrc setup that works on any server.
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Fixing "command not found" Errors
Diagnose and fix "command not found" on Linux. Covers PATH, hash cache, sudo secure_path, pip --user, and cron with practical templates.
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Package Management Basics: apt and yum
Practical guide to apt (Debian/Ubuntu) and yum/dnf (RHEL/CentOS) package management. Side-by-side command map, install/update workflows, and troubleshooting steps.
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dnf Package Management - Modern Tool for Fedora and RHEL-Based Systems
Learn dnf, the standard package manager for Fedora and RHEL-based systems. Covers install, update, remove, search, repo management, module streams, and rollback with practical examples.
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Package Management Troubleshooting: Resolving Dependency Errors
Systematically fix apt and yum/dnf dependency errors. Covers dpkg repair, lock file conflicts, GPG key issues, and a step-by-step diagnosis flow for Ubuntu, CentOS, and Fedora.
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Git and Linux Basics - Version Control
Learn Git basics on Linux: install, configure, init, add, commit, and push. Covers Permission denied, SSH key auth, line endings, and exec bit pitfalls specific to Linux.
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Network Commands Basics - Checking Connectivity with ip and ifconfig
Learn the difference between ip and ifconfig and isolate "no network" issues layer by layer: link → IP → route → reachability → DNS, plus a net-tools migration cheat sheet.
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netstat and ss Basics: Monitoring Ports and Connections
Learn how to check listening ports, established connections, and TCP states with netstat and ss, including a netstat-to-ss migration cheat sheet for everyday use.
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Network Troubleshooting in Practice - ping, traceroute, and dig
A 3-step approach to diagnosing network failures: ping for reachability, traceroute for routing, dig for DNS. Covers common patterns — gateway stops, DNS failures, and blocked ports — with real examples.
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curl and wget Basics - HTTP Communication from the Command Line
Learn with Linny-senpai and Lina! Understand the curl vs wget split, the -O/-o trap, redirect follow with -L, header inspection with -I, JSON POST, and Bearer token auth — all from a beginner's perspective.
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SSH Key Authentication Setup - Passwordless and Secure Login
Generate an ED25519 key pair with ssh-keygen, deploy the public key using ssh-copy-id, and connect without a password. Covers permissions, ~/.ssh/config for multi-server management, and ssh-agent for passphrase caching.
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~/.ssh/config Tips - Organizing Your SSH Connection Settings
Replace long ssh commands with short aliases using ~/.ssh/config. Covers ProxyJump for bastion host connections, per-host IdentityFile selection, KeepAlive settings, and Host * for global defaults.
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Ubuntu scp/rsync Basics: File Transfer Between Servers
Learn how to transfer files between servers using scp and rsync on Ubuntu. Includes copy-paste templates for common scenarios.
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realpath and readlink
Learn how realpath and readlink resolve symlinks and relative paths into absolute paths. Covers -f / -e / -m, --relative-to, and safe scripting patterns.
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rsync in Practice: Backups and Mirroring
Use rsync differential sync for real work - mirroring with --delete, generational backups with --link-dest, excludes, and bandwidth control done safely.
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openssl Command Basics
Learn practical openssl in one pass. Create certificates, compute hashes, encrypt files with AES, and check server certificate expiry with copy-paste commands.
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GPG Basics: Encrypting, Decrypting, and Signing Files
Encrypt and decrypt files with gpg and verify signatures. Learn when to use public-key vs password mode, with copy-paste examples.
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SSH Port Forwarding: Local, Remote, and Dynamic Tunnels
Use -L, -R, and -D to reach databases behind bastions, expose local apps, and run a SOCKS proxy with safe, repeatable SSH tunnels.
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tcpdump Basics
Capture packets with tcpdump. From first capture to BPF filters, pcap files, and Wireshark - a practical playbook for diagnosing network issues.
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lsof - Listing Open Files and Ports
Find which process holds a file, socket, or port with lsof. Solve device is busy, port conflicts, and deleted-but-open files with copy-paste commands.
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Getting Started with nc (netcat) - The Versatile Tool for Port Testing and Debugging
Learn nc (netcat) for port testing, simple server setup, file transfer, and banner grabbing. Practical debugging patterns for Linux network diagnostics.
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iptables and nftables Basics - Introduction to Packet Filtering
Learn the fundamentals of iptables and nftables on Linux. Set up SSH and HTTP rules, block ports, and persist your firewall configuration on Ubuntu.
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Firewall Configuration Basics: Getting Started with ufw and firewalld
Learn how to configure Linux firewalls with ufw (Ubuntu) and firewalld (RHEL/CentOS). Covers port rules, default policies, zones, and practical patterns for web and database servers.
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/etc/hosts and /etc/resolv.conf - Understanding DNS Resolution Priority
How /etc/hosts and /etc/resolv.conf shape DNS resolution on Linux — priority rules in nsswitch.conf, systemd-resolved, and practical override patterns.
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nmcli: Managing Networks from the Command Line
Manage NetworkManager with nmcli — check status, connect to Wi-Fi, set static IPs, and activate connections with copy-paste commands.
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traceroute and mtr: Tracing Network Paths and Finding the Slow Hop
Use traceroute to map the path and mtr to measure per-hop loss and latency. Learn what * means and how to read loss to find the slow or lossy segment.
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modprobe and lsmod: Managing Kernel Modules
Use lsmod to inspect loaded kernel modules and modprobe to load or remove them with dependencies. Covers modinfo, blacklist, and load-at-boot.
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Linux Error Messages Dictionary
A reverse-lookup dictionary of common Linux error messages. Quickly find the cause and fix for command not found, Permission denied, No space left on device, OOM, and more.
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sed Basics - Text Substitution with the Stream Editor
Master the five core sed patterns (substitute, delete, print, address, multi-expression), the safe pattern for in-place editing with `-i.bak`, and when to choose BRE vs ERE.
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Getting Started with sort and uniq
Learn with Linny-senpai and Lina! Master sort and uniq for sorting, deduplicating, and counting data, including the classic `sort | uniq -c | sort -rn` frequency ranking pattern.
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xargs in Practice - Converting Standard Input to Command Arguments
Master xargs to "paste" pipe contents into the argument slot of the next command. Learn safe patterns with find -print0 | xargs -0, the -I {} placeholder, and -P parallel execution while avoiding common pitfalls.
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jq Basics - How to Process JSON in the Shell
A practical guide for shaping JSON from curl and APIs with jq. Master filters, select, map, raw vs compact output, and safe patterns for piping JSON in production scripts.
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cut, paste, and tr Basics - Column Extraction and Character Conversion
Use cut to extract CSV/TSV columns, paste to merge files side by side, and tr to translate or delete characters. Combine them in pipelines for powerful text processing.
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diff and patch Basics - Getting and Applying Diffs
Learn how to generate file diffs with diff -u and apply them with patch. Covers unified diff format, directory comparison, -p0 vs -p1 strip levels, dry runs, and reverting with patch -R.
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comm and join: Comparing and Joining Files
Use comm to show common lines and differences across two files in 3 columns, and join to merge rows on a shared key. Includes the sorted-input gotcha.
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pv: Monitoring Pipe Progress with a Progress Bar
Use pv (Pipe Viewer) to put a progress bar on any pipe. End the anxiety of staring at a silent dd or cp wondering if it is still running.
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hexdump and xxd: Inspecting Binary Data in Hex
Compare hexdump, xxd, and od at a glance. Use -C, xxd -r, and od -t x1z to peek at binary, spot CRLF and BOM bytes, and edit bytes by hand.
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Getting Started with tee - Splitting Command Output
Learn with Lina and Linny-senpai! Save pipeline output to a file while keeping it flowing to the next command. Covers -a append, multiple file targets, the sudo tee pattern for root-owned files, and using tee as a pipeline debugger.
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awk One-Liners - 30 Practical Patterns for Real-World Use
30 practical awk one-liners organized by use case. Field extraction, aggregation, log analysis, and CSV processing — copy-paste ready patterns for real-world use.
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column, pr, and fmt - Understanding Text Formatting Commands
Learn Linux text formatting commands column, pr, and fmt — align tabular data, paginate output for printing, and reformat paragraph text on the command line.
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Reading Logs with less, more, and tail
Learn with Lina and Linny-senpai! Tired of `cat` scrolling past? Master less for page navigation and search, tail for the newest entries, and tail -f for real-time log monitoring.
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Getting Started with stat - Reading File Metadata
Learn to read stat output on Linux. Covers atime/mtime/ctime timestamp differences, inode number usage, format options for scripting, and filesystem-level statistics with stat -f.
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find -exec vs xargs: Choosing the Right Approach
Learn when to use find -exec (semicolon vs plus form) vs xargs. Covers the -print0 | xargs -0 safety pattern for filenames with spaces, parallel execution with -P, and practical one-liners for common file management tasks.
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Understanding du vs df - Measuring Disk Usage Correctly
A beginner-friendly walkthrough of how du and df differ. Learn why "df is full but du doesn't add up" — covering deleted-open files, mount boundaries, and root-reserved blocks with a practical investigation playbook.
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ncdu: Interactive Disk Usage Analyzer
A beginner-friendly walkthrough of ncdu. Navigate the largest directories with arrow keys, delete files safely on the spot, see how it differs from du, and scan remote servers over ssh.
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bat: A cat Clone with Syntax Highlighting
A beginner-friendly walkthrough of bat. Display files with syntax highlighting, line numbers, and Git diff markers; fix the Ubuntu batcat naming issue; strip decorations to behave like cat; and colorize man pages.
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split Command: Splitting and Joining Large Files
A beginner-friendly walkthrough of split. Break a file that is too big to handle into pieces, join them back with cat, and verify nothing was lost. Covers size, line, and count splits plus numbered suffixes and integrity checks.
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seq Command: Generating Sequences of Numbers
How do you build the numbers 1 to 100? A beginner-friendly walkthrough of seq. Generate sequences and feed them into for loops to create numbered files. Covers ranges, increments, zero padding, separators, and counting down.
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top and htop Mastery - Identifying System Bottlenecks
Read top's summary lines in 30 seconds to decide whether the bottleneck is CPU, memory, or I/O. Master %us/%sy/%wa thresholds, htop's tree view, filters, and F-keys for production-grade triage.
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Getting Started with tmux - Terminal Multiplexing Basics
Learn tmux fundamentals through a friendly dialogue between Lina and Linny-senpai. Keep your work alive after SSH disconnects, master the session/window/pane hierarchy, the prefix key (Ctrl+b), and detach/attach with beginner-friendly examples.
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strace Basics - Tracing System Calls for Troubleshooting
Learn to trace system calls with strace on Linux. Filter by call type, attach to running processes with -p, interpret errno values like ENOENT and EACCES, and diagnose Permission denied and connection failures in minutes.
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vmstat, iostat, and sar - Linux Performance Analysis Tools
Learn to identify CPU, memory, and I/O bottlenecks using three complementary tools. Use vmstat for a system-wide overview, iostat to pinpoint slow devices by await and util%, and sar to review historical trends after an incident.
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Setting Up Aliases - How to Shorten Linux Commands
Learn with Lina and Linny-senpai! Create short nicknames for long commands using alias, persist them in .bashrc, and remove them with unalias.
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Understanding .bashrc and .profile Load Order
Learn with Linny-senpai and Lina! Why aliases disappear over SSH, the difference between login and interactive shells, and how to reload settings instantly with source — all explained for beginners.
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How to Write systemd Unit Files - Registering Custom Services
Learn to daemonize scripts and applications using systemd. Covers the [Unit], [Service], and [Install] sections, ExecStart, Restart policies, EnvironmentFile, and the full systemctl enable/start workflow.
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Symbolic Links and Hard Links - Understanding File References in Linux
Learn the difference between symbolic and hard links. Covers the ln command, inodes, reference counting, cross-filesystem constraints, and practical patterns like dotfiles and version-managed directories.
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Why cron Is Not Running - Troubleshooting crontab on Linux
Fix cron jobs that aren't running on Linux. Learn how to check crontab, view logs, and avoid common PATH and permission pitfalls.
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at Command: One-Time Job Scheduling on Linux
Schedule one-time jobs with the at command. Confirm atd, write time specs, manage jobs with atq and atrm, and know when to use at instead of cron.
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systemd Timer vs cron: Choosing the Right Scheduler
Compare systemd timer and cron for Linux job scheduling. Prefer systemd timer for logging, dependencies, and missed-run recovery; cron for simple one-liners.
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How to Use systemctl - Linux Service Management Guide
Manage Linux services with systemctl. Learn status, start, restart, and enable commands for Nginx, Apache, SSH, and other services.
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How to Read Log Files - Introduction to System Log Analysis
Learn to read Linux log files in /var/log/. Covers syslog, auth.log, kern.log structure plus practical commands — tail -f, grep, less — for effective log analysis and troubleshooting.
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logrotate Basics - Keeping Logs Manageable with Automatic Rotation
Learn logrotate config structure and key directives. Covers rotate, compress, delaycompress, postrotate, and how to debug with dry-run mode on Linux.
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/tmp Cleanup Best Practices - tmpfiles.d and systemd-tmpfiles
Manage /tmp cleanup with systemd-tmpfiles and tmpfiles.d. Write declarative rules for automatic deletion, permissions, and boot-time directory creation.
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Disk Management Basics - Inspecting Storage with fdisk and lsblk
Learn how to inspect Linux storage layout using fdisk -l and lsblk. Covers partition types, block device trees, device naming conventions, and when to use df vs du for disk space investigation.
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lsblk and blkid: Inspecting Block Devices and UUIDs
Map device topology with lsblk and read UUID, LABEL, and FS type with blkid. Learn how to grab a stable device identifier for fstab.
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Mount and fstab Basics - How to Attach Filesystems in Linux
Learn how to use the mount command and /etc/fstab. Covers attaching devices to directories, using UUID for safe device identification, and writing persistent mounts that survive reboots.
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LVM and Partition Management in Practice: Flexible Storage Operations
LVM and partition management guide for Linux. Learn to create PV, VG, and LV, extend volumes online, use snapshots, and manage storage flexibly.
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Swap Management - Avoiding Memory Exhaustion in Linux
Learn what Linux swap is, how to create a swapfile, tune swappiness for your workload, and diagnose OOM killer events before they take down production.
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dd Command: Disk Imaging and Safe Usage
Clone disks and write ISO images to USB with dd safely. Verify the target with lsblk and avoid wiping the wrong device, from imaging to progress display.
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fzf: Fuzzy Finder for the Command Line
fzf is a command-line fuzzy finder. Search history with CTRL-R, pick files with CTRL-T. Covers install, shell integration, search syntax, and preview.
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ripgrep (rg): Fast Code Search
ripgrep (rg) is a fast grep alternative that respects .gitignore. Covers the difference from grep, install, type/glob filtering, context, and replacement preview.
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date Command - Formatting and Calculating Dates
Learn with Lina and Linny-senpai! Use date to show the current time, format output with %Y, calculate dates like yesterday or 3 days ago, convert epoch seconds, and switch time zones.
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Command Substitution: Capturing Output with $(...)
Learn with Lina and Linny-senpai! Capture command output into variables with `$(...)`, see how it differs from backticks, and understand why you should quote it.
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Globbing and Wildcards
Learn with Lina and Linny-senpai! Understand how `*`, `?`, and `[]` differ, how brace expansion is separate, and avoid the traps with extglob, dotfiles, and no-match behavior.
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test and [[ ]] - Conditionals in Shell Scripts
A practical guide to test, [ ], and [[ ]]. Master string, numeric, and file comparisons and avoid quoting bugs with copy-paste templates.
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Exit Codes: Using $? and && ||
Learn with Lina and Linny-senpai! Understand exit status, check results with $?, and branch your commands with && and || in a beginner-friendly walkthrough.
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timeout Command Basics
Learn with Lina and Linny-senpai! Limit how long a command runs and automatically stop hung commands, with exit status 124 and forced kill via -k, explained for beginners.
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chmod: Numeric vs Symbolic Modes
Learn with Lina and Linny-senpai! Understand chmod numeric mode (644, 755) and symbolic mode (u+x, go-w), the r=4 w=2 x=1 math, and when to use each in a beginner-friendly walkthrough.
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rename Command: Bulk Renaming
Learn with Lina and Linny-senpai! Rename many files at once with the rename command in a beginner-friendly walkthrough, covering the -n dry-run, s/// substitution, and the Perl vs util-linux versions.
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base64 Command: Encoding and Decoding
Learn the base64 command with Lina and Linny-senpai. Encode and decode strings and files, avoid the echo newline trap, control wrapping with -w, and learn the key point that base64 is not encryption.
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flock: Preventing Concurrent Runs with File Locks
Stop cron jobs and scripts from overlapping with flock. Exclusive locks, timeouts, and self-locking patterns explained for real-world ops.
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inotifywait: Watching Filesystem Events
Trigger automation on file changes with inotifywait. close_write vs modify, recursive watch limits, and a copy-paste processing loop.
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sshfs: Mounting Remote Filesystems over SSH
Mount a remote directory locally over SSH with sshfs. Installation, auto-reconnect, fstab automation, unmounting, and common fixes from a practical angle.
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History Expansion: Reusing Commands with !! and !$
From !! / !$ to !string / !:n / :h:t:r / ^old^new^. Use bash history expansion to reuse past commands fast, explained for beginners.
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Brace Expansion: {1..10} and More
Learn with Lina and Linny-senpai! Master {1..10} and {a,b,c} to create numbered files and directories fast, explained step by step for beginners.
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Bash Arrays: Indexed and Associative Arrays
Learn bash indexed and associative arrays step by step: declaring, accessing, looping, and editing elements, plus quoting and sparse-array pitfalls.
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tac and rev - Reversing Lines and Characters
Learn with Lina and Linny-senpai! tac flips the order of lines, rev flips the characters inside each line. Two reverse commands with opposite jobs, explained for beginners.
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yes Command: Automating Confirmations
Learn with Lina and Linny-senpai! When typing y to every "Are you sure?" prompt gets old, see how yes auto-answers them, why it is dangerous, and the safer alternatives.
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env Command
Run a command with a modified environment without touching your shell. Set variables temporarily, use env -i / -u / -C, and write portable shebangs.
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GNU parallel
Run shell commands in parallel to speed up batch work. Placeholders, job control, output ordering, and joblog resume explained, with how parallel differs from xargs.
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ionice
Stop backups and rsync from slowing down your server. Use ionice to set idle/best-effort/realtime classes, apply to running PIDs, and check the BFQ scheduler when it has no effect.
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tar in Practice: Incremental Backups & Exclusions
A practical tar workflow for incremental backups. Use --listed-incremental for level-0/level-1 diffs, --exclude to skip noise, and -C plus --strip-components to control where and how archives extract.
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nl Command: Numbering Lines
Learn the nl command through a friendly dialogue. Add line numbers to text, see how nl differs from cat -n on blank lines, and tune width, separator, start number, and format.
Read more →🩺 Practical Troubleshooting
Reverse-Lookup ReferenceError and incident articles have moved to a dedicated reverse-lookup category. Look up Permission denied, No space left, SSH failures, high CPU load, memory pressure, DNS issues by symptom.
🐧 Master Skills Through Practice!
After learning the theory, practice using actual commands. You can learn experientially at Penguin Gym Linux.