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A collection of awesome lists, manuals, blogs, hacks, one-liners, cli/web tools and more.
📔 What is it?
This list is a collection of various materials that I use every day in my work. It contains a lot of useful information gathered in one piece.
🚻 For whom?
It is intended for everyone and anyone - especially for System and Network Administrators, DevOps, Pentesters or Security Researchers.
ℹ️ Contributing
A few simple rules for this project:
- inviting and clear
- not tiring
- useful
These below rules may be better:
- easy to contribute to (Markdown + HTML ...)
- easy to find (no TOC, maybe it's worth creating them?)
Url marked * is temporary unavailable. Please don't delete it without confirming that it has permanently expired.
Before add pull request please see this. All suggestions/PR are welcome!
☑️ Todo
- Add useful shell functions
- Add one-liners for collection tools (eg. CLI Tools)
- Generate book pdf format
💢 The Book of Secret Knowledge (Chapters)
CLI Tools
▪️ Shells
🔸 Oh My ZSH! - the best framework for managing your Zsh configuration.
🔸 bash-it - framework for using, developing and maintaining shell scripts and custom commands for your daily work.
🔸 Oh My Fish - the Fishshell framework.
▪️ Managers
🔸 Midnight Commander - visual file manager, licensed under GNU General Public License.
🔸 screen - full-screen window manager that multiplexes a physical terminal.
🔸 tmux - terminal multiplexer, lets you switch easily between several programs in one terminal.
🔸 tmux-cssh - sets a comfortable and easy to use functionality, clustering and synchronizing virtual tmux-sessions.
▪️ Network
🔸 nmap - free and open source (license) utility for network discovery and security auditing.
🔸 masscan - the fastest Internet port scanner, spews SYN packets asynchronously.
🔸 hping - command-line oriented TCP/IP packet assembler/analyzer.
🔸 mtr - functionality of the 'traceroute' and 'ping' programs in a single network diagnostic tool.
🔸 netcat - networking utility which reads and writes data across network connections, using the TCP/IP protocol.
🔸 tcpdump - powerful command-line packet analyzer.
🔸 tshark - dump and analyze network traffic (wireshark cli).
🔸 ngrep - is like GNU grep applied to the network layer.
🔸 bmon - monitoring and debugging tool to capture networking related statistics and prepare them visually.
🔸 iptraf-ng - is a console-based network monitoring program for Linux that displays information about IP traffic.
🔸 iPerf3 - is a tool for active measurements of the maximum achievable bandwidth on IP networks.
🔸 Nemesis - packet manipulation CLI tool; craft and inject packets of several protocols.
🔸 packetfu - a mid-level packet manipulation library for Ruby.
🔸 Scapy - packet manipulation library; forge, send, decode, capture packets of a wide number of protocols.
🔸 aria2 - is a lightweight multi-protocol & multi-source command-line download utility.
🔸 Lynx - is a text browser for the World Wide Web.
▪️ Network (DNS)
🔸 fierce - a DNS reconnaissance tool for locating non-contiguous IP space.
🔸 sublist3r - fast subdomains enumeration tool for penetration testers.
🔸 amass - tool obtains subdomain names by scraping data sources, crawling web archives and more.
🔸 namebench - provides personalized DNS server recommendations based on your browsing history.
▪️ Network (HTTP)
🔸 Curl - command line tool and library for transferring data with URLs.
🔸 kurly - is an alternative to the widely popular curl program, written in Golang.
🔸 HTTPie - a user-friendly HTTP client.
🔸 wuzz - interactive cli tool for HTTP inspection.
🔸 htrace.sh - shell script to debugging http/https; ssllabs, mozilla observatory, testssl.sh and nmap nse support.
🔸 httpstat - visualizes curl statistics in a way of beauty and clarity.
🔸 siege - is an http load testing and benchmarking utility.
🔸 bombardier - fast cross-platform HTTP benchmarking tool written in Go.
🔸 gobench - http/https load testing and benchmarking tool.
🔸 gobuster - free and open source directory/file & DNS busting tool written in Go
▪️ SSL/Security
🔸 gnutls-cli - client program to set up a TLS connection to some other computer.
🔸 sslyze
- fast and powerful SSL/TLS server scanning library.
🔸 sslscan - tests SSL/TLS enabled services to discover supported cipher suites.
🔸 testssl.sh - testing TLS/SSL encryption anywhere on any port.
🔸 spiped - is a utility for creating symmetrically encrypted and authenticated pipes between socket addresses.
▪️ Auditing Tools
🔸 lynis - battle-tested security tool for systems running Linux, macOS, or Unix-based operating system.
🔸 LinEnum - scripted Local Linux Enumeration & Privilege Escalation Checks.
🔸 Rkhunter - scanner tool for Linux systems that scans backdoors, rootkits and local exploits on your systems.
▪️ System Diagnostics/Debuggers
🔸 strace - diagnostic, debugging and instructional userspace utility for Linux.
🔸 DTrace - is a performance analysis and troubleshooting tool.
🔸 ltrace - is a library call tracer, used to trace calls made by programs to library functions.
🔸 sysdig - system exploration and troubleshooting tool with first class support for containers.
🔸 glances - cross-platform system monitoring tool written in Python.
🔸 htop - interactive text-mode process viewer for Unix systems. It aims to be a better 'top'.
🔸 atop - ASCII performance monitor. Includes statistics for CPU, memory, disk, swap, network, and processes.
🔸 lsof - displays in its output information about files that are opened by processes.
🔸 FlameGraph - stack trace visualizer.
🔸 lsofgraph - small utility to convert Unix lsof output to a graph showing FIFO and UNIX interprocess communication.
▪️ Log Analyzers
🔸 GoAccess - real-time web log analyzer and interactive viewer that runs in a terminal.
🔸 ngxtop - real-time metrics for nginx server.
▪️ Databases
🔸 usql - universal command-line interface for SQL databases.
🔸 pgcli - postgres CLI with autocompletion and syntax highlighting.
🔸 mycli - terminal client for MySQL with autocompletion and syntax highlighting.
▪️ TOR
🔸 Nipe - script to make Tor Network your default gateway.
🔸 multitor - a tool that lets you create multiple TOR instances with a load-balancing.
▪️ Other
🔸 incron - is an inode-based filesystem notification technology.
🔸 tldr - simplified and community-driven man pages.
GUI Tools
▪️ Network
🔸 Wireshark - is the world’s foremost and widely-used network protocol analyzer.
▪️ Password Managers
🔸 KeePassXC - store your passwords safely and auto-type them into your everyday websites and apps.
▪️ Text editors
🔸 Sublime Text - is a lightweight, cross-platform code editor known for its speed, ease of use.
🔸 Atom - a hackable text editor for the 21st Century.
Web Tools
▪️ SSL/Security
🔸 SSL Server Test - free online service performs a deep analysis of the configuration of any SSL web server.
🔸 SSL Server Test (DEV) - free online service performs a deep analysis of the configuration of any SSL web server.
🔸 ImmuniWeb® SSLScan - test SSL/TLS (PCI DSS, HIPAA and NIST).
🔸 urlscan.io - service to scan and analyse websites.
🔸 Report URI - monitoring security policies like CSP and HPKP.
🔸 CSP Evaluator - allows developers and security experts to check if a Content Security Policy.
🔸 Useless CSP - public list about CSP in some big players (might make them care a bit more).
🔸 Why No HTTPS? - list of the world's top 100 websites by Alexa rank not automatically redirecting insecure requests.
🔸 cipherli.st - strong ciphers for Apache, Nginx, Lighttpd and more.
🔸 badssl.com - memorable site for testing clients against bad SSL configs.
🔸 tlsfun.de - registered for various tests regarding the TLS/SSL protocol.
🔸 Common CA Database - repository of information about CAs, and their root and intermediate certificates.
🔸 CERTSTREAM - real-time certificate transparency log update stream.
🔸 crt.sh - discovers certificates by continually monitoring all of the publicly known CT.
🔸 SSL Check - scan your website for non-secure content.
▪️ Privacy
🔸 privacytools.io - provides knowledge and tools to protect your privacy against global mass surveillance.
🔸 DNS Privacy Test Servers - DNS privacy recursive servers list (with a 'no logging' policy).
▪️ HTTP Headers
🔸 Security Headers - analyse the HTTP response headers (with rating system to the results).
🔸 Observatory by Mozilla - set of tools to analyze your website.
🔸 Enable CORS - enable cross-origin resource sharing.
▪️ DNS
🔸 ViewDNS - one source for free DNS related tools and information.
🔸 DNSlytics - online investigation tool.
🔸 DNS Spy - monitor, validate and verify your DNS configurations.
🔸 Find subdomains online - find subdomains for security assessment penetration test.
🔸 DNSdumpster - dns recon & research, find & lookup dns records.
🔸 DNS Table online - search for DNS records by domain, IP, CIDR, ISP.
🔸 PTRarchive.com - this site is responsible for the safekeeping of historical reverse DNS records.
🔸 xip.ip - wildcard DNS for everyone.
▪️ Mail
🔸 MX Toolbox - all of your MX record, DNS, blacklist and SMTP diagnostics in one integrated tool.
🔸 blacklistalert - checks to see if your domain is on a Real Time Spam Blacklist.
🔸 MultiRBL - complete IP check for sending Mailservers.
▪️ PGP Keyservers
🔸 SKS OpenPGP Key server - includes a highly-efficient reconciliation algorithm for keeping the keyservers synchronized.
▪️ Mass scanners (search engines)
🔸 Censys - platform that helps information security practitioners discover, monitor, and analyze devices.
🔸 Shodan - the world's first search engine for Internet-connected devices.
🔸 Shodan 2000 - if you use Shodan for everyday work, be sure to see it - looks for randomly generated data from Shodan.
🔸 GreyNoise - mass scanner (such as Shodan and Censys).
🔸 ZoomEye - search engine for cyberspace that lets the user find specific network components.
🔸 FOFA - is a cyberspace search engine.
🔸 onyphe - is a search engine for open-source and cyber threat intelligence data collected.
🔸 binaryedge - it scan the entire internet space and create real-time threat intelligence streams and reports.
🔸 hunter - lets you find email addresses in seconds and connect with the people that matter for your business.
🔸 wigle - is a submission-based catalog of wireless networks. All the networks. Found by Everyone.
🔸 PublicWWW - find any alphanumeric snippet, signature or keyword in the web pages HTML, JS and CSS code.
🔸 IntelTechniques - this repository contains hundreds of online search utilities.
🔸 GhostProject? - search by full email address or username.
🔸 Buckets by Grayhatwarfar - database with public search for Open Amazon S3 Buckets and their contents.
🔸 Vigilante.pw - the breached database directory.
🔸 builtwith - find out what websites are built with.
▪️ Net-tools
🔸 Netcraft - detailed report about the site, helping you to make informed choices about their integrity.
🔸 RIPE NCC - not-for-profit membership association, a Regional Internet Registry and the secretariat for the RIPE.
🔸 Robtex - uses various sources to gather public information about IP numbers, domain names, host names, routes etc.
🔸 Security Trails - APIs for Security Companies, Researchers and Teams.
🔸 Online Curl - curl test, analyze HTTP Response Headers.
🔸 Ping.eu - online Ping, Traceroute, DNS lookup, WHOIS and others.
🔸 Network-Tools - network tools for webmasters, IT technicians & geeks.
🔸 URL Encode/Decode - tool from above to either encode or decode a string of text.
🔸 Uncoder - the online translator for search queries on log data.
🔸 XSS String Encoder - for generating XSS code to check your input validation filters against XSS.
🔸 RegExr - online tool to learn, build, & test Regular Expressions (RegEx / RegExp).
🔸 Hardenize - deploy the security standards.
🔸 VirusTotal - analyze suspicious files and URLs to detect types of malware.
▪️ Code parsers/playgrounds
🔸 ShellCheck - finds bugs in your shell scripts.
🔸 explainshell - get interactive help texts for shell commands.
🔸 jsbin - live pastebin for HTML, CSS & JavaScript and more.
🔸 PHP Sandbox - test your PHP code with this code tester.
🔸 Repl.it - an instant IDE to learn, build, collaborate, and host all in one place.
▪️ Performance
🔸 GTmetrix - analyze your site’s speed and make it faster.
🔸 Sucuri loadtimetester - test here the
performance of any of your sites from across the globe.
🔸 Pingdom Tools - analyze your site’s speed around the world.
▪️ Passwords
🔸 Gotcha? - list of 1.4 billion accounts circulates around the Internet.
🔸 have i been pwned? - check if you have an account that has been compromised in a data breach.
▪️ CVE/Exploits databases
🔸 CVE Mitre - list of publicly known cybersecurity vulnerabilities.
🔸 CVE Details - CVE security vulnerability advanced database.
🔸 Exploit DB - CVE compliant archive of public exploits and corresponding vulnerable software.
🔸 0day.today - exploits market provides you the possibility to buy zero-day exploits and also to sell 0day exploits.
🔸 sploitus - the exploit and tools database.
Manuals/Howtos/Tutorials
▪️ Bash
🔸 pure-bash-bible - a collection of pure bash alternatives to external processes.
🔸 The Bash Hackers Wiki - hold documentation of any kind about GNU Bash.
🔸 Shell & Utilities - describes the commands and utilities offered to application programs by POSIX-conformant systems.
▪️ Programming
🔸 F’Awk Yeah! - advanced sed and awk usage (Parsing for Pentesters 3).
▪️ Unix & Network
🔸 nixCraft - linux and unix tutorials for new and seasoned sysadmin.
🔸 TecMint - the ideal Linux blog for Sysadmins & Geeks.
🔸 Omnisecu - Free Networking, System Administration and Security Tutorials.
🔸 Unix Toolbox - collection of Unix/Linux/BSD commands and tasks which are useful for IT work or for advanced users.
▪️ System hardening
🔸 Security Harden CentOS 7 - this walks you through the steps required to security harden CentOS.
🔸 CentOS 7 Server Hardening Guide - great guide for hardening CentOS; familiar with OpenSCAP.
▪️ Security
🔸 OWASP - worldwide not-for-profit charitable organization focused on improving the security of software.
🔸 OWASP ASVS 3.0.1 - OWASP Application Security Verification Standard Project.
🔸 OWASP ASVS 3.0.1 Web App - simple web app that helps developers understand the ASVS requirements.
🔸 Hacking Articles - LRaj Chandel's Security & Hacking Blog.
🔸 AWS security tools - make your AWS cloud environment more secure.
🔸 Rawsec's CyberSecurity Inventory - an inventory of tools and resources about CyberSecurity.
🔸 Application Security Wiki - is an initiative to provide all application security related resources at one place.
🔸 The Illustrated TLS Connection - every byte of a TLS connection explained and reproduced.
▪️ Web Apps
🔸 Mozilla Web Security - help operational teams with creating secure web applications.
▪️ Other
🔸 CTF Series : Vulnerable Machines - the steps below could be followed to find vulnerabilities and exploits.
🔸 How to start RE/malware analysis? - collection of some hints and useful links for the beginners.
🔸 LZone Cheat Sheets - all cheat sheets.
🔸 Dan’s Cheat Sheets’s - massive cheat sheets documentation.
🔸 The C10K problem - it's time for web servers to handle ten thousand clients simultaneously, don't you think?
🔸 Bank Grade Security - when companies say they have "Bank Grade Security" they imply that it is a good thing.*
🔸 HTTPS on Stack Overflow - this is the story of a long journey regarding the implementation of SSL.
🔸 Julia's Drawings - some drawings about programming and unix world, zines about systems & debugging tools.
🔸 DEF CON Media Server - great stuff from DEFCON 26.
🔸 BGP Meets Cat - after 3072 hours of manipulating BGP, Job Snijders has succeeded in drawing a Nyancat.
🔸 HTTPS in the real world - great tutorial explain how HTTPS works in the real world.
🔸 Hidden directories - hidden directories and files as a source of sensitive information about web application.
Blogs
▪️ Geeky Blogs
🔸 Brendan Gregg's Blog - Brendan Gregg is an industry expert in computing performance and cloud computing.
🔸 Gynvael "GynDream" Coldwind - Gynvael is a IT security engineer at Google.
🔸 Michał "lcamtuf" Zalewski - "white hat" hacker, computer security expert.
🔸 Mattias Geniar - developer, Sysadmin, Blogger, Podcaster and Public Speaker.
🔸 Nick Craver - Software Developer and Systems Administrator for Stack Exchange.
🔸 Robert Penz - IT security Expert.
🔸 Scott Helme - Security Researcher, international speaker and founder of securityheaders.com and report-uri.com.
🔸 Kacper Szurek - Detection Engineer at ESET.
🔸 Troy Hunt - Microsoft Regional Director and Microsoft Most Valuable Professional for Developer Security.
🔸 Linux Audit - the Linux security blog about Auditing, Hardening and Compliance by Michael Boelen.
🔸
Linux Security Expert - trainings, howtos, checklists, security tools and more.
🔸 The Grymoire - collection of useful incantations for wizards, be you computer wizards, magicians, or whatever.
🔸 raymii.org - linux/unix sysadmin specializing in building high availability cloud environments.
▪️ A piece of history
🔸 How to Do Things at ARL - how to configure modems, scan images, record CD-ROMs, and other useful techniques.
Systems/Services
▪️ Systems
🔸 Slackware - the most "Unix-like" Linux distribution.
🔸 OpenBSD - multi-platform 4.4BSD-based UNIX-like operating system.
🔸 HardenedBSD - HardenedBSD aims to implement innovative exploit mitigation and security solutions.
🔸 Kali Linux - Linux distribution used for Penetration Testing, Ethical Hacking and network security assessments.
🔸 Backbox Linux - penetration test and security assessment oriented Ubuntu-based Linux distribution.
▪️ HTTP(s) Services
🔸 Varnish HTTP Cache - HTTP accelerator designed for content-heavy dynamic web sites.
🔸 Nginx - open source web and reverse proxy server that is similar to Apache, but very light weight.
▪️ Security/hardening
🔸 Emerald Onion - seattle-based encrypted-transit internet service provider.
🔸 Unbound - validating, recursive, and caching DNS resolver (with TLS).
🔸 Knot Resolver - caching full resolver implementation, including both a resolver library and a daemon.
🔸 Vulnreport - open-source pentesting management and automation platform by Salesforce Product Security.
Networks
▪️ Tools
🔸 CapAnalysis - web visual tool to analyze large amounts of captured network traffic (PCAP analyzer).
▪️ Labs
🔸 NRE Labs - learn automation by doing it. Right now, right here, in your browser.
Awesome Lists
🔸 Awesome Sysadmin - amazingly awesome open source sysadmin resources.
🔸 Awesome Shell - awesome command-line frameworks, toolkits, guides and gizmos.
🔸 Movies for Hackers - list of movies every hacker & cyberpunk must watch.
🔸 Awesome Pcaptools - collection of tools developed by other researchers to process network traces.
🔸 SecLists - collection of multiple types of lists used during security assessments, collected in one place.
🔸 Command-line-text-processing - from finding text to search and replace, from sorting to beautifying text and more.
🔸 Awesome Scalability - best practices in building High Scalability, High Availability, High Stability and more.
🔸 Awesome Postgres - list of awesome PostgreSQL software, libraries, tools and resources.
🔸 Free Security eBooks - list of a Free Security and Hacking eBooks.
Hacking/Penetration Testing
▪️ Pentesters arsenal tools
🔸 Metasploit - tool and framework for pentesting system, web and many more, contains a lot a ready to use exploit.
🔸 Burp Suite - tool for testing Web application security, intercepting proxy to replay, inject, scan and fuzz HTTP requests.
🔸 OWASP Zed Attack Proxy - intercepting proxy to replay, inject, scan and fuzz HTTP requests.
🔸 Nikto2 - web server scanner which performs comprehensive tests against web servers for multiple items.
🔸 sqlmap - tool that automates the process of detecting and exploiting SQL injection flaws.
🔸 Faraday - an Integrated Multiuser Pentest Environment.
🔸 ctf-tools - some setup scripts for security research tools.
▪️ Pentests bookmarks collection
🔸 PTES - the penetration testing execution standard.
🔸 Brute XSS - master the art of Cross Site Scripting.
🔸 Offensive Security Bookmarks - security bookmarks collection, all that things I need to pass OSCP.
🔸 Awesome Pentest Cheat Sheets - collection of the cheat sheets useful for pentesting.
🔸 Awesome Hacking - awesome lists for hackers, pentesters and security researchers.
🔸 Awesome Hacking Resources - collection of hacking/penetration testing resources to make you better.
🔸 Hacking Cheat Sheet - author hacking and pentesting notes.
🔸 Awesome Pentest - collection of awesome penetration testing resources, tools and other shiny things.
🔸 Pentest Bookmarks - there are a LOT of pentesting blogs.
🔸 PayloadsAllTheThings - a list of useful payloads and bypass for Web Application Security and Pentest/CTF.
🔸 Pentesting Tools Cheat Sheet - a quick reference high level overview for typical penetration testing engagements.
🔸 SQL Injection Cheat Sheet - detailed technical information about the many different variants of the SQL Injection.
🔸 Entersoft Knowledge Base - great and detailed reference about vulnerabilities.
🔸 HTML5 Security Cheatsheet - a collection of HTML5 related XSS attack vectors.
🔸 GTFOBins - list of Unix binaries that can be exploited by an attacker to bypass local security restrictions.
🔸 Guifre Ruiz Notes - collection of security, system, network and pentest cheatsheets.
▪️ Bounty programs
🔸 Bounty Factory - European bug bounty platform based on the legislation and rules in force in European countries.
🔸 Openbugbounty - allows any security researcher reporting a vulnerability on any website.
🔸 hackerone - global hacker community to surface the most relevant security issues.
🔸 bugcrowd - crowdsourced cybersecurity for the enterprise.
🔸 Crowdshield - crowdsourced Security & Bug Bounty Management.
▪️ Web Training Apps (local installation)
🔸 OWASP-VWAD - comprehensive and well maintained registry of all known vulnerable web applications.
🔸 Metasploitable 2 - vulnerable web application amongst security researchers.
🔸 DVWA - PHP/MySQL web application that is damn vulnerable.
🔸 OWASP Mutillidae II - free, open source, deliberately vulnerable web-application.
🔸 OWASP Juice Shop Project - the most bug-free vulnerable application in existence.
🔸 OWASP WebGoat Project - insecure web application maintained by OWASP designed to teach web app security.
🔸 Security Ninjas - open source application security training program.
🔸 hackazon - a modern vulnerable web app.
🔸 dvna - damn vulnerable NodeJS application.
🔸 Google Gruyere - web application exploits and defenses.
🔸 Bodhi - is a playground focused on learning the exploitation of client-side web vulnerabilities.
▪️ Labs (ethical hacking platforms/trainings)
🔸 Offensive Security - true performance-based penetration testing training for over a decade.
🔸 Hack The Box - online platform allowing you to test your penetration testing skills.
🔸 Hacking-Lab - online ethical hacking, computer network and security challenge platform.
🔸 pwnable.kr - non-commercial wargame site which provides various pwn challenges regarding system exploitation.
🔸 Pwnable.tw - is a wargame site for hackers to test and expand their binary exploiting skills.
🔸 Silesia Security Lab - high quality security testing services.
🔸 Practical Pentest Labs - pentest lab, take your Hacking skills to the next level.
🔸 Root Me - the fast, easy, and affordable way to train your hacking skills.
🔸 rozwal.to - a great platform to train your pentesting skills.
🔸 TryHackMe - learning Cyber Security made easy.
🔸 OverTheWire - can help you to learn and practice security concepts in the form of fun-filled games.
🔸 Wizard Labs - is an online Penetration Testing Lab.
🔸 PentesterLab - provides vulnerable systems that can be used to test and understand vulnerabilities.
🔸 RingZer0 - tons of challenges designed to test and improve your hacking skills.
🔸 Ubeeri - preconfigured lab environments.
🔸 Pentestit - emulate an IT infrastructure of real companies for a legal pen testing and improving penetration testing skills.
Your daily knowledge and news
▪️ RSS Readers
🔸 Feedly - organize, read and share what matters to you.
▪️ Security
🔸 Security Newsletter - security news as a weekly digest (email notifications).
🔸 Google Online Security Blog - the latest news and insights from Google on security and safety on the Internet.
🔸 Qualys Blog - expert network security guidance and news.
🔸 DARKReading - connecting the Information Security Community.
🔸 publiclyDisclosed - public disclosure watcher who keeps you up to date about the recently disclosed bugs.
🔸 Packet Storm - information security services, news, files, tools, exploits, aAdvisories and whitepapers.
🔸 Sekurak - about security, penetration tests, vulnerabilities and many others (PL/EN).
🔸 nf.sec - basic aspects and mechanisms of Linux operating system security (PL).
Other Cheat Sheets
DNS Servers list (privacy)
| IP | URL |
|---|---|
84.200.69.80 |
dns.watch |
94.247.43.254 |
opennic.org |
64.6.64.6 |
verisign.com |
89.233.43.71 |
censurfridns.dk |
1.1.1.1 |
cloudflare.com |
94.130.110.185 |
dnsprivacy.at |
Build your own DNS Servers
🔸 Unbound DNS Tutorial - a validating, recursive, and caching DNS server.
🔸 Knot Resolver on Fedora - how to get faster and more secure DNS resolution with Knot Resolver on Fedora.
🔸 DNS-over-HTTPS - tutorial to setup your own DNS-over-HTTPS (DoH) server.
🔸 DNS Servers - how (and why) i run my own DNS Servers.
🔸 DNS Privacy Server - running your own DoT or DoH server this page provides some ideas.
One-liners
Table of Contents
Tool: terminal
Reload shell without exit
exec $SHELL -l
Close shell keeping all subprocess running
disown -a && exit
Exit without saving shell history
kill -9 $$
unset HISTFILE && exit
Perform a branching conditional
true && echo success
false || echo failed
Pipe stdout and stderr to separate commands
some_command > >(/bin/cmd_for_stdout) 2> >(/bin/cmd_for_stderr)
Redirect stdout and stderr each to separate files and print both to the screen
(some_command 2>&1 1>&3 | tee errorlog ) 3>&1 1>&2 | tee stdoutlog
List of commands you use most often
history | \
awk '{CMD[$2]++;count++;}END { for (a in CMD)print CMD[a] " " CMD[a]/count*100 "% " a;}' | \
grep -v "./" | \
column -c3 -s " " -t | \
sort -nr | nl | head -n 20
Quickly backup a file
cp filename{,.orig}
Empty a file (truncate to 0 size)
>filename
Delete all files in a folder that don't match a certain file extension
rm !(*.foo|*.bar|*.baz)
Pass multi-line string to a file
# cat >filename ... - overwrite file
# cat >>filename ... - append to file
cat > filename << __EOF__
data data data
__EOF__
Edit a file on a remote host using vim
vim scp://user@host//etc/fstab
Create a directory and change into it at the same time
mkd () { mkdir -p "$@" && cd "$@"; }
Convert uppercase files to lowercase files
rename 'y/A-Z/a-z/' *
Print a row of characters across the terminal
printf "%`tput cols`s" | tr ' ' '#'
Show shell history without line numbers
history | cut -c 8-
fc -l -n 1 | sed 's/^\s*//'
Run command(s) after exit session
cat > /etc/profile << __EOF__
_after_logout() {
username=$(whoami)
for _pid in $(ps afx | grep sshd | grep "$username" | awk '{print $1}') ; do
kill -9 $_pid
done
}
trap _after_logout EXIT
__EOF__
Generate a sequence of numbers
for ((i=1; i<=10; i+=2)) ; do echo $i ; done
# alternative: seq 1 2 10
for ((i=5; i<=10; ++i)) ; do printf '%02d\n' $i ; done
# alternative: seq -w 5 10
Tool: mount
Mount a temporary ram partition
mount -t tmpfs tmpfs /mnt -o size=64M
-t- filesystem type-o- mount options
Remount a filesystem as read/write
mount -o remount,rw /
Tool: fuser
Kills a process that is locking a file
fuser -k filename
Show what PID is listening on specific port
fuser -v 53/udp
Tool: ps
Show a 4-way scrollable process tree with full details
ps awwfux | less -S
Processes per user counter
ps hax -o user | sort | uniq -c | sort -r
Tool: find
Find files that have been modified on your system in the past 60 minutes
find / -mmin 60 -type f
Find all files larger than 20M
find / -type f -size +20M
Find duplicate files (based on MD5 hash)
find -type f -exec md5sum '{}' ';' | sort | uniq --all-repeated=separate -w 33
Change permission only for files
cd /var/www/site && find . -type f -exec chmod 766 {} \;
cd /var/www/site && find . -type f -exec chmod 664 {} +
Change permission only for directories
cd /var/www/site && find . -type d -exec chmod g+x {} \;
cd /var/www/site && find . -type d -exec chmod g+rwx {} +
Find files and directories for specific user
find . -user <username> -print
Find files and directories for all without specific user
find . \!-user <username> -print
Delete older files than 60 days
find . -type f -mtime +60 -delete
Recursively remove all empty sub-directories from a directory
find . -depth -type d -empty -exec rmdir {} \;
How to find all hard links to a file
find </path/to/dir> -xdev -samefile filename
Recursively find the latest modified files
find . -type f -exec stat --format '%Y :%y %n' "{}" \; | sort -nr | cut -d: -f2- | head
Tool: top
Use top to monitor only all processes with the specific string
top -p $(pgrep -d , <str>)
<str>- process containing str (eg. nginx, worker)
Tool: strace
Track child process
strace -f -p $(pidof glusterfsd)
Track process after 30 seconds
timeout 30 strace $(< /var/run/zabbix/zabbix_agentd.pid)
Track child process and redirect output to a file
ps auxw | grep 'sbin/[a]pache' | awk '{print " -p " $2}' | xargs strace -o /tmp/strace-apache-proc.out
Track the open request of a network port
strace -f -e trace=bind nc -l 80
Track the open request of a network port (show TCP/UDP)
strace -f -e trace=network nc -lu 80
Tool: kill
Kill a process running on port
kill -9 $(lsof -i :<port> | awk '{l=$2} END {print l}')
Tool: diff
Compare two directory trees
diff <(cd directory1 && find | sort) <(cd directory2 && find | sort)
Tool: tail
Annotate tail -f with timestamps
tail -f file | while read ; do echo "$(date +%T.%N) $REPLY" ; done
Analyse an Apache access log for the most common IP addresses
tail -10000 access_log | awk '{print $1}' | sort | uniq -c | sort -n | tail
Analyse web server log and show only 5xx http codes
tail -n 100 -f /path/to/logfile | grep "HTTP/[1-2].[0-1]\" [5]"
Tool: tar
System backup with exclude specific directories
cd /
tar -czvpf /mnt/system$(date +%d%m%Y%s).tgz --directory=/ \
--exclude=proc/* --exclude=sys/* --exclude=dev/* --exclude=mnt/* .
System backup with exclude specific directories (pigz)
cd /
tar cvpf /backup/snapshot-$(date +%d%m%Y%s).tgz --directory=/ \
--exclude=proc/* --exclude=sys/* --exclude=dev/* \
--exclude=mnt/* --exclude=tmp/* --use-compress-program=pigz .
Tool: dump
System backup to file
dump -y -u -f /backup/system$(date +%d%m%Y%s).lzo /
Restore system from lzo file
cd /
restore -rf /backup/system$(date +%d%m%Y%s).lzo
Tool: cpulimit
Limit the cpu usage of a process
cpulimit -p pid -l 50
Tool: pwdx
Show current working directory of a process
pwdx <pid>
Tool: taskset
Start a command on only one CPU core
taskset -c 0 <command>
Tool: tr
Show directories in the PATH, one per line
tr : '\n' <<<$PATH
Tool: chmod
Remove executable bit from all files in the current directory
chmod -R -x+X *
Restore permission for /bin/chmod
# 1:
cp /bin/ls chmod.01
cp /bin/chmod chmod.01
./chmod.01 700 file
# 2:
/bin/busybox chmod 0700 /bin/chmod
# 3:
setfacl --set u::rwx,g::---,o::--- /bin/chmod
Tool: who
Find last reboot time
who -b
Tool: screen
Start screen in detached mode
screen -d -m [<command>]
Tool: du
Show 20 biggest directories with 'K M G'
du | \
sort -r -n | \
awk '{split("K M G",v); s=1; while($1>1024){$1/=1024; s++} print int($1)" "v[s]"\t"$2}' | \
head -n 20
Tool: inotifywait
Init tool everytime a file in a directory is modified
while true ; do inotifywait -r -e MODIFY dir/ && ls dir/ ; done;
Tool: openssl
Testing connection to remote host
echo | openssl s_client -connect google.com:443 -showcerts
Testing connection to remote host (with SNI support)
echo | openssl s_client -showcerts -servername google.com -connect google.com:443
Testing connection to remote host with specific ssl version
openssl s_client -tls1_2 -connect google.com:443
Testing connection to remote host with specific ssl cipher
openssl s_client -cipher 'AES128-SHA' -connect google.com:443
Generate private key
# _ciph: des3, aes
( _ciph="des3" ; _fd="private.key" ; _len="2048" ; \
openssl genrsa -${_ciph} -out ${_fd} ${_len} )
Remove password from private key
( _fd="private.key" ; _fd_unp="private_unp.key" ; \
openssl rsa -in ${_fd} -out ${_fd_unp} )
Get public key from private key
( _fd="private.key" ; _fd_pub="public.key" ; \
openssl rsa -pubout -in ${_fd} -out ${_fd_pub} )
Generate private key + csr
( _fd="private.key" ; _fd_csr="request.csr" ; _len="2048" ; \
openssl req -out ${_fd_csr} -new -newkey rsa:${_len} -nodes -keyout ${_fd} )
Generate csr
( _fd="private.key" ; _fd_csr="request.csr" ; \
openssl req -out ${_fd_csr} -new -key ${_fd} )
Generate csr (metadata from exist certificate)
( _fd="private.key" ; _fd_csr="request.csr" ; _fd_crt="cert.crt" ; \
openssl x509 -x509toreq -in ${_fd_crt} -out ${_fd_csr} -signkey ${_fd} )
Generate csr with -config param
( _fd="private.key" ; _fd_csr="request.csr" ; \
openssl req -new -sha256 -key ${_fd} -out ${_fd_csr} \
-config <(
cat <<-EOF
[req]
default_bits = 2048
prompt = no
default_md = sha256
req_extensions = req_ext
distinguished_name = dn
[ dn ]
C=<two-letter ISO abbreviation for your country>
ST=<state or province where your organization is legally located>
L=<city where your organization is legally located>
O=<legal name of your organization>
OU=<section of the organization>
CN=<fully qualified domain name>
[ req_ext ]
subjectAltName = @alt_names
[ alt_names ]
DNS.1 = <fully qualified domain name>
DNS.2 = <next domain>
DNS.3 = <next domain>
EOF
))
Convert DER to PEM
( _fd_der="cert.crt" ; _fd_pem="cert.pem" ; \
openssl x509 -in ${_fd_der} -inform der -outform pem -out ${_fd_pem} )
Convert PEM to DER
( _fd_der="cert.crt" ; _fd_pem="cert.pem" ; \
openssl x509 -in ${_fd_pem} -outform der -out ${_fd_der} )
Checking whether the private key and the certificate match
(openssl rsa -noout -modulus -in private.key | openssl md5 ; openssl x509 -noout -modulus -in certificate.crt | openssl md5) | uniq
Tool: gnutls-cli
Testing connection to remote host (with SNI support)
gnutls-cli -p 443 google.com
Testing connection to remote host (without SNI support)
gnutls-cli --disable-sni -p 443 google.com
Tool: secure-delete
Secure delete with shred
shred -vfuz -n 10 file
shred --verbose --random-source=/dev/urandom -n 1 /dev/sda
Secure delete with scrub
scrub -p dod /dev/sda
scrub -p dod -r file
Secure delete with badblocks
badblocks -s -w -t random -v /dev/sda
badblocks -c 10240 -s -w -t random -v /dev/sda
Secure delete with secure-delete
srm -vz /tmp/file
sfill -vz /local
sdmem -v
swapoff /dev/sda5 && sswap -vz /dev/sda5
Tool: dd
Show dd status every so often
dd <dd_params> status=progress
watch --interval 5 killall -USR1 dd
Redirect output to a file with dd
echo "string" | dd of=filename
Tool: curl
curl -Iks https://www.google.com
-I- show response headers only-k- insecure connection when using ssl-s- silent mode (not display body)
curl -Iks --location -X GET -A "x-agent" https://www.google.com
--location- follow redirects-X- set method-A- set user-agent
curl -Iks --location -X GET -A "x-agent" --proxy http://127.0.0.1:16379 https://www.google.com
--proxy [socks5://|http://]- set proxy server
Check DNS and HTTP trace with headers for specific domains
### Set domains and external dns servers.
_domain_list=(google.com) ; _dns_list=("8.8.8.8" "1.1.1.1")
for _domain in "${_domain_list[@]}" ; do
printf '=%.0s' {1..48}
echo
printf "[\\e[1;32m+\\e[m] resolve: %s\\n" "$_domain"
for _dns in "${_dns_list[@]}" ; do
# Resolve domain.
host "${_domain}" "${_dns}"
echo
done
for _proto in http https ; do
printf "[\\e[1;32m+\\e[m] trace + headers: %s://%s\\n" "$_proto" "$_domain"
# Get trace and http headers.
curl -Iks -A "x-agent" --location "${_proto}://${_domain}"
echo
done
done
unset _domain_list _dns_list
Tool: httpie
http -p Hh https://www.google.com
-p- print request and response headersH- request headersB- request bodyh- response headersb- response body
http -p Hh --follow --max-redirects 5 --verify no https://www.google.com
-F, --follow- follow redirects--max-redirects N- maximum for--follow--verify no- skip SSL verification
http -p Hh --follow --max-redirects 5 --verify no --proxy http:http://127.0.0.1:16379 https://www.google.com
--proxy [http:]- set proxy server
Tool: ssh
Compare a remote file with a local file
ssh user@host cat /path/to/remotefile | diff /path/to/localfile -
SSH connection through host in the middle
ssh -t reachable_host ssh unreachable_host
Run command over ssh on remote host
cat > cmd.txt << __EOF__
cat /etc/hosts
__EOF__
ssh host -l user $(<cmd.txt)
Get public key from private key
ssh-keygen -y -f ~/.ssh/id_rsa
Get all fingerprints
ssh-keygen -l -f .ssh/known_hosts
Ssh authentication with user password
ssh -o PreferredAuthentications=password -o PubkeyAuthentication=no user@remote_host
Ssh authentication with publickey
ssh -o PreferredAuthentications=publickey -o PubkeyAuthentication=yes -i id_rsa user@remote_host
Simple recording SSH session
function _ssh_sesslog() {
_sesdir="<path/to/session/logs>"
mkdir -p "${_sesdir}" && \
ssh $@ 2>&1 | tee -a "${_sesdir}/$(date +%Y%m%d).log"
}
# Alias:
alias ssh='_ssh_sesslog'
Using Keychain for SSH logins
### Delete all of ssh-agent's keys.
function _scl() {
/usr/bin/keychain --clear
}
### Add key to keychain.
function _scg() {
/usr/bin/keychain /path/to/private-key
source "$HOME/.keychain/$HOSTNAME-sh"
}
Tool: linux-dev
Testing remote connection to port
timeout 1 bash -c "</dev/<proto>/<host>/<port>" >/dev/null 2>&1 ; echo $?
<proto- set protocol (tcp/udp)<host>- set remote host<port>- set destination port
Read and write to TCP or UDP sockets with common bash tools
exec 5<>/dev/tcp/<host>/<port>; cat <&5 & cat >&5; exec 5>&-
Tool: tcpdump
tcpdump -ne -i eth0 -Q in host 192.168.252.1 and port 443
-n- don't convert addresses-e- print the link-level headers-i [iface|any]- set interface-Q|-D [in|out|inout]- choose send/receive direction (-D- for old tcpdump versions)host [ip|hostname]- set host, also[host not][and|or]- set logicport [1-65535]- set port number, also[port not]
tcpdump -ne -i eth0 -Q in host 192.168.252.1 and port 443 -c 5 -w tcpdump.pcap
-c [num]- capture only num number of packets-w [filename]- write packets to file,-r [filename]- reading from file
Tool: tcpick
Analyse packets in real-time
while true ; do tcpick -a -C -r dump.pcap ; sleep 2 ; clear ; done
Tool: ngrep
ngrep -d eth0 "www.google.com" port 443
-d [iface|any]- set interface[domain]- set hostnameport [1-65535]- set port number
ngrep -d eth0 "www.google.com" (host 10.240.20.2) and (port 443)
(host [ip|hostname])- filter by ip or hostname(port [1-65535])- filter by port number
ngrep -d eth0 -qt -O ngrep.pcap "www.google.com" port 443
-q- quiet mode (only payloads)-t- added timestamps-O [filename]- save output to file,-I [filename]- reading from file
ngrep -d eth0 -qt 'HTTP' 'tcp'
HTTP- show http headerstcp|udp- set protocol[src|dst] host [ip|hostname]- set direction for specific node
ngrep -l -q -d eth0 -i "User-Agent: curl*"
-l- stdout line buffered-i- case-insensitive search
Tool: hping3
hping3 -V -p 80 -s 5050 <scan_type> www.google.com
-V|--verbose- verbose mode-p|--destport- set destination port-s|--baseport- set source port<scan_type>- set scan type-F|--fin- set FIN flag, port open if no reply-S|--syn- set SYN flag-P|--push- set PUSH flag-A|--ack- set ACK flag (use when ping is blocked, RST response back if the port is open)-U|--urg- set URG flag-Y|--ymas- set Y unused flag (0x80 - nullscan), port open if no reply-M 0 -UPF- set TCP sequence number and scan type (URG+PUSH+FIN), port open if no reply
hping3 -V -c 1 -1 -C 8 www.google.com
-c [num]- packet count-1- set ICMP mode-C|--icmptype [icmp-num]- set icmp type (default icmp-echo = 8)
hping3 -V -c 1000000 -d 120 -S -w 64 -p 80 --flood --rand-source <remote_host>
--flood- sent packets as fast as possible (don't show replies)--rand-source- random source address mode-d --data- data size-w|--win- winsize (default 64)
Tool: netcat
nc -kl 5000
-l- listen for an incoming connection-k- listening after client has disconnected>filename.out- save receive data to file (optional)
nc 192.168.0.1 5051 < filename.in
< filename.in- send data to remote host
nc -vz 10.240.30.3 5000
-v- verbose output-z- scan for listening daemons
nc -vzu 10.240.30.3 1-65535
-u- scan only udp ports
Transfer data file (archive)
server> nc -l 5000 | tar xzvfp -
client> tar czvfp - /path/to/dir | nc 10.240.30.3 5000
Launch remote shell
server> nc -l 5000 -e /bin/bash
client> nc 10.240.30.3 5000
Simple file server
while true ; do nc -l 5000 | tar -xvf - ; done
Simple minimal HTTP Server
while true ; do nc -l -p 1500 -c 'echo -e "HTTP/1.1 200 OK\n\n $(date)"' ; done
Simple HTTP Server
Restarts web server after each request - remove
whilecondition for only single connection.
cat > index.html << __EOF__
<!doctype html>
<head>
<meta charset="utf-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge,chrome=1">
<title></title>
<meta name="description" content="">
<meta name="viewport" content="width=device-width, initial-scale=1">
</head>
<body>
<p>
Hello! It's a site.
</p>
</body>
</html>
__EOF__
server> while : ; do \
(echo -ne "HTTP/1.1 200 OK\r\nContent-Length: $(wc -c <index.html)\r\n\r\n" ; cat index.html;) | \
nc -l -p 5000 \
; done
-p- port number
Simple HTTP Proxy (single connection)
#!/usr/bin/env bash
if [[ $# != 2 ]] ; then
printf "%s\\n" \
"usage: ./nc-proxy listen-port bk_host:bk_port"
fi
_listen_port="$1"
_bk_host=$(echo "$2" | cut -d ":" -f1)
_bk_port=$(echo "$2" | cut -d ":" -f2)
printf " lport: %s\\nbk_host: %s\\nbk_port: %s\\n\\n" \
"$_listen_port" "$_bk_host" "$_bk_port"
_tmp=$(mktemp -d)
_back="$_tmp/pipe.back"
_sent="$_tmp/pipe.sent"
_recv="$_tmp/pipe.recv"
trap 'rm -rf "$_tmp"' EXIT
mkfifo -m 0600 "$_back" "$_sent" "$_recv"
sed "s/^/=> /" <"$_sent" &
sed "s/^/<= /" <"$_recv" &
nc -l -p "$_listen_port" <"$_back" | \
tee "$_sent" | \
nc "$_bk_host" "$_bk_port" | \
tee "$_recv" >"$_back"
server> chmod +x nc-proxy && ./nc-proxy 8080 192.168.252.10:8000
lport: 8080
bk_host: 192.168.252.10
bk_port: 8000
client> http -p h 10.240.30.3:8080
HTTP/1.1 200 OK
Accept-Ranges: bytes
Cache-Control: max-age=31536000
Content-Length: 2748
Content-Type: text/html; charset=utf-8
Date: Sun, 01 Jul 2018 20:12:08 GMT
Last-Modified: Sun, 01 Apr 2018 21:53:37 GMT
Create a single-use TCP or UDP proxy
### TCP -> TCP
nc -l -p 2000 -c "nc [ip|hostname] 3000"
### TCP -> UDP
nc -l -p 2000 -c "nc -u [ip|hostname] 3000"
### UDP -> UDP
nc -l -u -p 2000 -c "nc -u [ip|hostname] 3000"
### UDP -> TCP
nc -l -u -p 2000 -c "nc [ip|hostname] 3000"
Tool: socat
Testing remote connection to port
socat - TCP4:10.240.30.3:22
-- standard input (STDIO)TCP4:<params>- set tcp4 connection with specific params[hostname|ip]- set hostname/ip[1-65535]- set port number
Redirecting TCP-traffic to a UNIX domain socket under Linux
socat TCP-LISTEN:1234,bind=127.0.0.1,reuseaddr,fork,su=nobody,range=127.0.0.0/8 UNIX-CLIENT:/tmp/foo
TCP-LISTEN:<params>- set tcp listen with specific params[1-65535]- set port numberbind=[hostname|ip]- set bind hostname/ipreuseaddr- allows other sockets to bind to an addressfork- keeps the parent process attempting to produce more connectionssu=nobody- set userrange=[ip-range]- ip range
UNIX-CLIENT:<params>- communicates with the specified peer socketfilename- define socket
Tool: lsof
Show process that use internet connection at the moment
lsof -P -i -n
Show process that use specific port number
lsof -i tcp:443
Lists all listening ports together with the PID of the associated process
lsof -Pan -i tcp -i udp
List all open ports and their owning executables
lsof -i -P | grep -i "listen"
Show all open ports
lsof -Pnl -i
Show open ports (LISTEN)
lsof -Pni4 | grep LISTEN | column -t
List all files opened by a particular command
lsof -c "process"
View user activity per directory
lsof -u username -a +D /etc
Show 10 Largest Open Files
lsof / | \
awk '{ if($7 > 1048576) print $7/1048576 "MB" " " $9 " " $1 }' | \
sort -n -u | tail | column -t
Tool: netstat
Graph # of connections for each hosts
netstat -an | \
grep ESTABLISHED | \
awk '{print $5}' | \
awk -F: '{print $1}' | \
grep -v -e '^[[:space:]]*$' | \
sort | uniq -c | \
awk '{ printf("%s\t%s\t",$2,$1) ; for (i = 0; i < $1; i++) {printf("*")}; print "" }'
Monitor open connections for specific port including listen, count and sort it per IP
watch "netstat -plan | grep :443 | awk {'print \$5'} | cut -d: -f 1 | sort | uniq -c | sort -nk 1"
Tool: rsync
Rsync remote data as root using sudo
rsync --rsync-path 'sudo rsync' username@hostname:/path/to/dir/ /local/
Tool: host
Resolves the domain name (using external dns server)
host google.com 9.9.9.9
Checks the domain administrator (SOA record)
host -t soa google.com 9.9.9.9
Tool: dig
Resolves the domain name (short output)
dig google.com +short
Lookup NS record for specific domain
dig @9.9.9.9 google.com NS
Query only answer section
dig google.com +nocomments +noquestion +noauthority +noadditional +nostats
Query ALL DNS Records
dig google.com ANY +noall +answer
DNS Reverse Look-up
dig -x 172.217.16.14 +short
Tool: network-other
Get all subnets for specific AS (Autonomous system)
AS="AS32934"
whois -h whois.radb.net -- "-i origin ${AS}" | \
grep "^route:" | \
cut -d ":" -f2 | \
sed -e 's/^[ \t]//' | \
sort -n -t . -k 1,1 -k 2,2 -k 3,3 -k 4,4 | \
cut -d ":" -f2 | \
sed -e 's/^[ \t]/allow /' | \
sed 's/$/;/' | \
sed 's/allow */subnet -> /g'
Resolves domain name from dns.google.com with curl and jq
_dname="google.com" ; curl -s "https://dns.google.com/resolve?name=${_dname}&type=A" | jq .
Tool: awk
Remove duplicate entries in a file without sorting
awk '!x[$0]++' filename
Exclude multiple columns using AWK
awk '{$1=$3=""}1' filename
Tool: sed
To print a specific line from a file
sed -n 10p /path/to/file
Remove a specific line from a file
sed -i 10d /path/to/file
# alternative (BSD): sed -i'' 10d /path/to/file
Remove a range of lines from a file
sed -i <file> -re '<start>,<end>d'
Tool: grep
Search for a "pattern" inside all files in the current directory
grep -rn "pattern"
grep -RnisI "pattern" *
fgrep "pattern" * -R
Remove blank lines from a file and save output to new file
grep . filename > newfilename
Except multiple patterns
grep -vE '(error|critical|warning)' filename
Show data from file without comments
grep -v ^[[:space:]]*# filename
Show data from file without comments and new lines
egrep -v '#|^$' filename