SysOps

A one-stop Linux troubleshooting reference organized by process/load, port/network, disk/memory, and logs/services, helping you quickly spot performance bottlenecks, connection anomalies, and resource hogs during live incidents.

A Vim operation reference covering cursor motion, text editing, search and replace, visual mode, and save/exit, aimed at developers and operators editing files on a server, including real-world tricks such as batch replacement and saving with sudo.

A Systemd service-management reference covering start/stop and boot-enabling, journalctl log viewing, timer scheduling, targets and runlevels, and resource limits, with the differences between easily-confused pairs such as reload vs restart and mask vs disable.

A Cron scheduling reference spanning the 5-field expression format, special characters and time macros, common examples, environment variables, and troubleshooting, flagging frequent pitfalls such as the OR relationship between day-of-month and day-of-week and the minimal default PATH.

A debugging reference for GitHub Actions, GitLab CI, and Jenkins pipelines, covering job reruns and log extraction, runner online status, cache and disk usage, and local reproduction with act or gitlab-runner exec.

An MQ operations reference for Kafka, RabbitMQ, RocketMQ, and Redis Pub/Sub, focused on the four high-frequency scenarios of locating consumer backlog, hunting connection leaks, diagnosing cluster state, and benchmarking throughput.

For anyone doing long-lived remote work over SSH, tmux keeps sessions, windows, and panes alive across disconnects — closing a window does not kill the work. This table groups create/delete/switch flows for sessions, windows and panes, copy-mode keystrokes, and common .tmux.conf settings.

grep, sed, and awk are the "three text-processing swords": grep matches, sed rewrites in place, and awk extracts and aggregates by column. This reference collects each tool's highest-frequency forms and keeps the classic pipeline chain (grep to filter, sed to substitute, awk to summarize), for anyone who lives in logs, configs, and CSV.

A tar archiving reference covering creating and extracting .gz/.bz2/.xz/.zst archives, exclusion of files, listing archive contents, incremental backups, and common pipeline tricks.

Whether you are shipping an HTTPS endpoint or debugging a TLS failure, OpenSSL is the tool: inspecting a certificate's validity and SANs, generating a CSR and self-signed cert, and testing an actual TLS handshake. This reference is organized around the certificate lifecycle and connection debugging for developers and ops configuring certs or chasing handshake errors.

Bash is the default entry point for automating ops and deploys, and the details that make a script robust — default variables, parameter expansion and string slicing, conditionals, and loops — are where the skill lives. This reference covers variables, branches, loops, functions, and common string/file operations for both writing scripts from scratch and debugging existing ones.

A chmod reference covering numeric and symbolic modes, recursive changes, common permission combinations, and the purpose and risks of SUID/SGID/Sticky special permissions.

A find reference covering search by name, type, size, time, permission, and owner, plus running actions on matches, with tips to avoid scanning irrelevant directories.

When a port refuses to start or a deleted file still pins disk space, lsof answers "who opened what": by process, port, user, or file. This reference covers the multi-axis lookups (listener + process, file-to-user, connections) and practical flags like +L1 for freeing files marked deleted-but-still-held.

For checking connection states, confirming what is listening, and counting per-protocol connections, netstat is the veteran Linux command, complementary to ss. This reference covers listing connections, filtering by TCP/UDP, listening ports, the routing table, and interface stats, and flags -p to pin down the owning process.

screen is the terminal multiplexer that ships with almost every Linux distribution, a lighter alternative to tmux. This reference covers creating, detaching, and reattaching sessions (Ctrl-a d to detach, -r to return), multiple windows and splits, plus the -x flag to share one session across two terminals — so a dropped SSH connection stops interrupting long-running work.

An awk reference covering built-in variables such as NR and NF, conditionals and loops, per-column extraction and aggregation, string functions, and typical patterns for processing logs and CSV.

Batch-editing configs, redacting logs, and in-place replacement with a backup are sed's territory — the "rewrite" partner to awk's "aggregate". This reference covers substitution, deletion, insert/append, addressing by range, extended regex, and the -i in-place edit with -i.bak backup.

A grep search reference covering basic and recursive search, regex vs fixed strings, context lines, inverse filtering, multiple patterns, and counting, with common performance and escaping notes.

A ps process-management reference covering filtering by user, command, and state, custom output columns, process trees and threads, and the difference between aux and -ef styles.

top is the first window that shows why a machine feels slow, and htop wraps the same data in friendlier keys. This reference covers sorting and filtering by CPU/memory, the interactive keys (P/M to sort, k to kill), batch-mode output to file, and how to read the load average and memory bars to tell pressure from noise.

A wget download reference covering basic downloads, resume support, retries and timeouts, recursive site mirroring, background downloads, and handling auth and HTTPS.

An scp and rsync file-transfer reference covering single-file and directory copies, incremental sync, preserving permissions and timestamps, resume and checksum, and when each tool fits best.

netcat (`nc`) is a Swiss-army knife for network checks: test whether a port responds, stand up a throwaway listener, relay between sockets, or move a file — without installing a server. This reference covers connect/scan, listen-and-echo, HTTP debugging, forwarding, and UDP mode, for quick connectivity checks under pressure.

A taskset CPU-affinity reference covering reading a process's current CPU mask, pinning a process to specific cores or a range, and tuning with the NUMA topology in mind.

ffmpeg is the de-facto standard for audio/video processing, covering transcoding, cutting, joining, extracting audio/subtitles, watermarking, and filtering in one tool. This reference covers format conversion, explicit encoders, cut/trim, audio and subtitle extraction, compression, and filters, plus the `-c copy` shortcut that skips re-encoding for speed.

A Zsh terminal-configuration reference covering common .zshrc settings, oh-my-zsh plugins and themes, aliases, autocompletion, history search, and prompt customization.

For encrypting files, signing messages, and signing Git commits, GnuPG is the local standard, and good key management is what actually keeps it usable. This reference covers key generation, import/export and revocation, encryption/decryption, sign/verify, and gpg-agent's passphrase cache.

An Ansible reference covering ad-hoc commands, inventory management, common modules (copy, template, service, shell), Playbook structure, and syntax and check validation.

Vagrant turns a machine image plus a Vagrantfile into a reproducible local VM that the whole team can share. This reference covers the init/up/ssh/destroy lifecycle, Vagrantfile settings, multi-machine definitions, and Provision automation, with notes on synced folders and port forwarding.

A Fish Shell reference covering its syntax differences from Bash, variables and functions, out-of-the-box autocompletion, aliases, and theme configuration.

An rclone reference for cloud storage, covering configuring a remote, copy and sync, checksum verification, filter rules, and encrypted backups.

For periodic scripts, scheduled backups, and log cleanup, cron is the most widespread Linux job scheduler — the five-field time syntax is the main hurdle. This reference covers the time format and special strings, common examples, crontab subcommands, environment variables, and troubleshooting hooks like log location and MAILTO.

Terraform manages infrastructure as code through declarative HCL, with init → plan → apply → destroy as the core loop. This reference covers that lifecycle, state-file management, variables and outputs, module references and remote backends, plus hygiene commands like fmt and validate.

On Windows, system administration and automation hinge on PowerShell's object pipeline — cmdlets return objects, not text, so you filter and act on properties directly. This reference covers common cmdlets and their Linux counterparts, file/process/service operations, and Invoke-Command remoting, to turn daily Windows ops into scripts.

An SSH handbook for engineers who need passwordless login, bastion hopping across environments, and linking their local machine to remote networks — covering ssh -i/-p/-vvv login debugging, ssh-keygen & ssh-copy-id key management, ~/.ssh/config aliases & ProxyJump, -L/-R/-D port forwarding, and the known_hosts and key-permission gotchas.

An Elasticsearch reference for cluster operators and search engineers, covering health checks, shard allocation diagnosis, index & lifecycle (ILM) management, document CRUD, search & query DSL, aggregation, slow-query analysis, and disk/red-cluster troubleshooting.

The Makefile's real value is its dependency graph — declaring prerequisites means only stale targets rebuild, which is why it also powers many non-C automation tasks. This reference covers variable assignment (= vs := vs ?=), targets and rules, pattern rules and automatic variables, conditionals and functions, plus common pitfalls like .PHONY.

An HTTPie reference: GET/POST requests, automatic JSON formatting, form and file uploads, authentication, and http/s sessions for everyday API testing.

An AWS CLI reference covering authentication and configuration, the EC2 instance lifecycle, S3 object operations, IAM users and policies, and common query and management commands across resources.

An rsync incremental-sync reference covering -a archive, -z compression, --delete mirroring, --exclude, --dry-run preview, and remote sync, with an eye on backup correctness.