📖 Guide

Cron — Complete Reference

Cron scheduling reference covering syntax, field values, crontab management, and common schedule patterns.

63 commands across 9 categories

Cron Syntax Special Strings Field Values Common Schedules Crontab Management Environment Output & Logging Best Practices Common Patterns

Cron Syntax

Command	Description
`* * * * *`	Five fields: minute hour day-of-month month day-of-week
`┌ minute (0-59)\n│ ┌ hour (0-23)\n│ │ ┌ day of month (1-31)\n│ │ │ ┌ month (1-12)\n│ │ │ │ ┌ day of week (0-7, 0&7=Sun)`	Field order reference
`*`	Wildcard — matches every value
`5,10,15`	List — matches specific values
`1-5`	Range — matches values 1 through 5
`/15` e.g. /15 * * * * → every 15 minutes	Step — every 15th value
`1-30/5`	Range with step — every 5th value from 1 to 30

Special Strings

Command	Description
`@reboot`	Run once at startup
`@yearly / @annually`	Run once a year (0 0 1 1 *)
`@monthly`	Run once a month (0 0 1 * *)
`@weekly`	Run once a week (0 0 * * 0)
`@daily / @midnight`	Run once a day (0 0 * * *)
`@hourly`	Run once an hour (0 * * * *)

Field Values

Command	Description
`Minute: 0-59`	Minute of the hour
`Hour: 0-23`	Hour of the day (0 = midnight)
`Day of Month: 1-31`	Day of the month
`Month: 1-12 or JAN-DEC`	Month (names are case-insensitive)
`Day of Week: 0-7 or SUN-SAT`	Day of week (0 and 7 both = Sunday)
`SUN=0, MON=1, TUE=2, WED=3, THU=4, FRI=5, SAT=6`	Day-of-week name to number mapping
`JAN=1, FEB=2, ..., NOV=11, DEC=12`	Month name to number mapping

Common Schedules

Command	Description
`0 * * * *`	Every hour (at minute 0)
`/5 * * *`	Every 5 minutes
`/15 * * *`	Every 15 minutes
`0 /2 * *`	Every 2 hours
`0 9 * * *`	Every day at 9:00 AM
`0 9 * * 1-5`	Weekdays at 9:00 AM
`0 0 * * 0`	Every Sunday at midnight
`0 0 1 * *`	First day of every month at midnight
`30 2 * * *`	Every day at 2:30 AM (common for backups)
`0 9,17 * * 1-5`	Weekdays at 9 AM and 5 PM

Crontab Management

Command	Description
`crontab -e`	Edit current user's crontab
`crontab -l`	List current user's crontab
`crontab -r`	Remove current user's crontab (⚠️ no confirmation)
`crontab -u username -e`	Edit another user's crontab (requires root)
`crontab file.txt`	Replace crontab with contents of file
`crontab -l > backup.txt`	Backup current crontab to file
`sudo ls /var/spool/cron/crontabs/`	List all user crontab files (Linux)
`cat /etc/crontab`	View system-wide crontab (includes user field)

Environment

Command	Description
`SHELL=/bin/bash`	Set shell for cron jobs (default is /bin/sh)
`PATH=/usr/local/bin:/usr/bin:/bin`	Set PATH (cron has minimal PATH by default)
`MAILTO=user@example.com`	Email output to this address
`MAILTO=""`	Disable email output
`HOME=/home/user`	Set working directory for jobs
`CRON_TZ=America/New_York`	Set timezone for cron schedule (some implementations)

Output & Logging

Command	Description
`* * * * * /script.sh > /dev/null 2>&1`	Suppress all output (stdout + stderr)
`* * * * * /script.sh >> /var/log/job.log 2>&1`	Append all output to log file
`* * * * * /script.sh 2>> /var/log/errors.log`	Log only errors (stderr)
`* * * * * /script.sh \| logger -t myjob`	Send output to syslog
`* * * * * date >> /tmp/cron.log && /script.sh >> /tmp/cron.log 2>&1`	Log with timestamp
`grep CRON /var/log/syslog`	Check cron execution history (Linux)

Best Practices

Command	Description
`/5 * * * /usr/bin/flock -n /tmp/job.lock /script.sh`	Prevent overlapping runs with flock
`0 3 * * * /usr/local/bin/backup.sh`	Use absolute paths for commands
`0 2 * * * sleep $((RANDOM \% 600)) && /script.sh`	Add random jitter to avoid thundering herd
`0 4 * * * chronic /script.sh`	Only email on error (using moreutils chronic)
`0 * * * * timeout 300 /script.sh`	Kill job if it runs longer than 5 minutes
`# Backup database nightly\n0 3 * * * /opt/scripts/backup.sh`	Always add comments describing the job

Common Patterns

Command	Description
`0 3 * * * /usr/bin/mysqldump -u root mydb > /backups/db.sql`	Nightly database backup
`/10 * * * /usr/bin/curl -sf https://hc-ping.com/UUID > /dev/null`	Healthcheck ping every 10 minutes
`0 5 * * * find /tmp -mtime +7 -delete`	Clean temp files older than 7 days
`0 /6 * * certbot renew --quiet`	Check SSL cert renewal every 6 hours
`0 0 * * 0 docker system prune -f`	Weekly Docker cleanup
`/30 * * * /usr/bin/rsync -a /src/ /backup/`	Sync files every 30 minutes
`0 8 * * 1 /opt/scripts/weekly-report.sh \| mail -s 'Report' user@co.com`	Monday morning report email

More Guides

Complete Git command reference — from basics to advanced workflows. Searchable, with examples.

Complete Vim/Vi command reference — modes, motions, editing, search, and advanced features.

Docker Commands

Complete Docker & Docker Compose command reference — containers, images, volumes, networks, and orchestration.

Regex Reference

Complete regular expression reference — syntax, patterns, quantifiers, groups, lookaheads, and common recipes.

Complete Linux/Bash command reference — file management, text processing, networking, system admin, and shell scripting.

Kubernetes Commands

Complete Kubernetes & kubectl command reference — pods, deployments, services, configmaps, and cluster management.

Python Reference

Complete Python reference — syntax, data structures, string methods, file I/O, comprehensions, and common patterns.

Complete SQL reference — queries, joins, aggregation, subqueries, indexes, and database management.

Nginx Reference

Complete Nginx configuration reference — server blocks, locations, proxying, SSL, load balancing, and caching.

Complete SSH reference — connections, key management, tunneling, config, SCP/SFTP, and security hardening.

Jenkins Reference

Complete Jenkins reference — pipeline syntax, Jenkinsfile, plugins, CLI, agents, and CI/CD patterns.

HTTP Headers Reference

Complete HTTP headers reference — request headers, response headers, caching, security, CORS, and content negotiation. Searchable, with examples.

PostgreSQL Reference

Comprehensive PostgreSQL reference — from connection basics to advanced features like JSONB, full-text search, window functions, and performance tuning.

Async Patterns Reference

Multi-language async/concurrency patterns — JavaScript, Python, Go, Rust, Java, and universal concurrency patterns.

Protobuf & gRPC Reference

Comprehensive reference for Protocol Buffers (proto3) and gRPC — message definitions, services, streaming, and common patterns.

JS Array Methods

Complete JavaScript Array methods reference — creating, searching, transforming, sorting, iterating, and common patterns. Searchable, with examples.

Tailwind CSS Reference

Complete Tailwind CSS reference — layout, spacing, typography, colors, responsive design, states, and common patterns. Searchable, with examples.

GraphQL Reference

Complete GraphQL reference — schema definition, types, queries, mutations, directives, fragments, and common patterns. Searchable, with examples.

VS Code Shortcuts

Complete VS Code keyboard shortcuts — editing, navigation, search, multi-cursor, terminal, debug, and more. Searchable, with Cmd/Ctrl notation.

CSS Grid Reference

Complete CSS Grid reference — container properties, item placement, grid functions, and common layout patterns. Searchable, with examples.

CSS Flexbox Reference

Complete CSS Flexbox reference — container properties, item properties, and common layout patterns. Searchable, with examples.

React Hooks Reference

Complete React Hooks reference — useState, useEffect, useContext, custom hooks, and common patterns. Searchable, with examples.

TypeScript Reference

Complete TypeScript reference — types, interfaces, generics, utility types, and advanced patterns. Searchable, with examples.

AWS CLI Reference

Complete AWS CLI reference — EC2, S3, IAM, Lambda, ECS, RDS, CloudFormation, and common operations.

Complete Go (Golang) reference — syntax, types, functions, concurrency, error handling, and common patterns.

PowerShell Reference

Complete PowerShell reference — cmdlets, pipelines, scripting, file operations, remote management, and Active Directory.

Complete Redis command reference — strings, hashes, lists, sets, sorted sets, pub/sub, transactions, and server management.

Terraform Commands

Complete Terraform reference — init, plan, apply, state management, modules, workspaces, and HCL syntax.

Ansible Commands

Complete Ansible reference — playbooks, modules, inventory, roles, vault, and ad-hoc commands.

Complete JavaScript reference — variables, types, operators, strings, arrays, objects, functions, async, DOM, ES6+, and more.

Complete CSS reference — selectors, box model, positioning, typography, animations, media queries, custom properties, and more.

Complete HTML reference — document structure, text content, forms, media, semantic elements, accessibility, and more.

Complete Java reference — data types, strings, collections, OOP, interfaces, exceptions, file I/O, streams, lambdas, and more.

Complete Bash reference — variables, strings, arrays, conditionals, loops, functions, file tests, I/O redirection, process management, and more.

Comprehensive Rust language cheat sheet covering ownership, traits, pattern matching, concurrency, and more.

Complete Markdown syntax reference for headings, formatting, links, tables, code blocks, and extensions.

YAML syntax reference covering scalars, collections, anchors, multi-line strings, and common patterns.

Curl command-line reference for HTTP requests, authentication, file transfers, debugging, and common API patterns.

Terminal multiplexer for managing multiple sessions, windows, and panes from a single terminal.

Powerful text processing language for pattern scanning, data extraction, and report generation.

Stream editor for filtering and transforming text, line by line.

Search for files and directories in a directory hierarchy with powerful filtering options.

Search text using patterns. Filter lines from files, command output, or streams with regular expressions.

Complete PHP cheat sheet covering syntax, OOP, arrays, PDO, and modern PHP 8.x features.

Complete C programming cheat sheet covering syntax, pointers, memory management, and standard library.

Complete C++ cheat sheet covering STL containers, OOP, templates, smart pointers, and modern C++ features.

Complete MySQL cheat sheet covering queries, joins, indexes, transactions, and administration.

Complete Sass/SCSS cheat sheet covering variables, mixins, functions, nesting, and modern module system.

Linux file permission commands and patterns for chmod.

Essential NumPy commands for array manipulation and numerical computing in Python.

Pandas cheat sheet for data manipulation, analysis, and transformation in Python.

Dart language cheat sheet covering syntax, types, OOP, null safety, and async patterns.

Laravel PHP framework cheat sheet for routing, Eloquent, Blade, Artisan, and more.

Comprehensive Node.js runtime reference covering modules, file system, HTTP, streams, and more.

Next.js App Router reference covering routing, data fetching, server components, and deployment.

MongoDB reference covering CRUD operations, aggregation, indexes, and administration.

Firebase reference covering Authentication, Firestore, Realtime Database, Cloud Functions, and Hosting.

Docker Compose reference covering CLI commands, service configuration, networking, volumes, and more.

Quick reference for jQuery selectors, DOM manipulation, events, AJAX, and more.

Quick reference for LaTeX document structure, math mode, formatting, and common packages.

Quick reference for XPath expressions, axes, predicates, and functions for XML/HTML querying.

Quick reference for Emmet abbreviations for lightning-fast HTML and CSS coding.

Quick reference for TOML configuration file syntax, types, tables, and common patterns.

Complete Prisma ORM cheat sheet — schema, queries, migrations, and CLI.

Complete GitHub Actions cheat sheet — workflows, triggers, jobs, and CI/CD patterns.

Complete npm cheat sheet — package management, scripts, publishing, and configuration.

Complete Supabase cheat sheet — auth, database, realtime, storage, and edge functions.

Complete Apache HTTP Server cheat sheet — virtual hosts, modules, rewrite rules, and SSL.

HTTP Status Codes

Complete reference of all standard HTTP response status codes with descriptions and use cases.

Complete ASCII character reference with decimal, hexadecimal, and character values.

Chrome DevTools

Essential Chrome DevTools shortcuts, commands, and workflows for web developers.

Complete Drizzle ORM reference for schema definition, queries, relations, migrations, and common patterns.

Complete Vercel CLI reference for deployment, project management, domains, environment variables, and configuration.

Production process manager for Node.js applications with built-in load balancer, monitoring, and zero-downtime reloads.

GNU Screen terminal multiplexer for persistent sessions, window management, and remote work.

Module bundler for JavaScript applications — loaders, plugins, code splitting, optimization, and dev server.

Next-generation frontend build tool with instant HMR, native ES modules, and optimized production builds via Rollup.

📖 Free, searchable command reference. Bookmark this page for quick access.