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Screenshot of the AdminLTE web interface for Pi-hole
|Initial release||June 15, 2015|
v4.3.2 / September 15, 2019
|Written in||Bash, PHP (optional web server), C (optional DNS server FTLDNS) and CSS|
|Licence||European Union Public Licence|
|Alexa rank||48,904 (May 2018)|
Pi-hole is a Linux network-level advertisement and Internet tracker blocking application which acts as a DNS sinkhole (and optionally a DHCP server), intended for use on a private network. It is designed for use on embedded devices with network capability, such as the Raspberry Pi, but it can be used on other machines running Linux and cloud implementations.
The Pi-hole project was created by Jacob Salmela as an open source alternative to the AdTrap in 2014 and was hosted on GitHub. Since then, several contributors have joined the project, most notably (based on the number of commits as of May 2018) dschaper, PromoFaux and DL6ER.
The Pi-hole makes use of dnsmasq, cURL, lighttpd, PHP and the AdminLTE Dashboard to block DNS requests for known tracking and advertising domains. The application serves as a DNS server for a private network (replacing any pre-existing DNS server provided by another device or the ISP), with the ability to block advertisements and tracking domains for users' devices. It obtains lists of advert and tracking domains from predefined sources (which can be modified by the user) that the Pi-hole uses to compare DNS queries to. If a match is found within any of the lists, or the user blacklist, the Pi-hole will refuse to resolve the requested domain and respond to the requesting device with a blank webpage.
Because Pi-hole blocks domains at the network level, it is able to block advertisements, such as banner adverts on a webpage, but it can also block adverts in unconventional locations, such as on Android, iOS and smart TVs.
Using VPN services, Pi-Hole can block domains without using a DNS filter setup in a router. Any device that supports VPN can use Pi-Hole on a cellular network or a home network without a DNS server configured. 
The nature of Pi-hole allows it to also block website domains in general by manually blacklisting the domain name. Likewise, domains can be whitelisted manually should a website's function be impaired by domains being blocked. Pi-hole can also function as a network monitoring tool, which can aid in troubleshooting DNS requests and faulty networking troubleshooting.
Difference from traditional advertisement blockers
Pi-hole functions similarly to a network firewall, meaning that adverts and tracking domains are blocked for all devices behind it, whereas traditional advertisement blockers only run in a user's browser, and remove adverts only on the same machine.
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