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docs/guides/ultimate-guides/torrents/ultimate-intro-to-torrents/index.md
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| slug: ultimate-intro-to-torrents | ||
| title: The Ultimate Intro to Torrents | ||
| tags: [torrent, tutorial] | ||
| authors: TechSquidTV | ||
| --- | ||
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| # What is a Torrent? | ||
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| More than likely, you are at least somewhat familiar with torrents. They are a way to download files from the internet. | ||
| But how do they work? What are the benefits of using torrents? How do you use them? Are they safe? Consider the following your guide to _torrents_. | ||
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| ## The Background of BitTorrent | ||
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| In the late 90s [Bram Cohen](https://en.wikipedia.org/wiki/Bram_Cohen) ([twitter](https://twitter.com/bramcohen)), a software developer, was working for a company called [MojoNation](<https://en.wikipedia.org/wiki/Mnet_(peer-to-peer_network)#MojoNation>) that was trying to create an encrypted decentralized file storage system for commercial-use. | ||
| Unfortunately, the company was faced with severe financial difficulties and would close in 2002. | ||
| Just before then, Cohen would realize that the technology he had been working on, while not a commercial success, could be used to create a new file sharing protocol that could dramatically speed up the process of sharing large files, such as [porn collections](https://www.wired.com/2005/01/bittorrent-2/). | ||
| Other peer-to-peer file sharing protocols at the time existed, such as ["Kazaa"](https://en.wikipedia.org/wiki/Kazaa), but they all were dependent on downloading complete files from a single user or "peer". | ||
| Especially at the time, with the majority of people having slow and unreliable internet access, the process of downloading large files could, and usually did, take a very long time. | ||
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| Cohen would leave MojoNation in 2001 and begin work on the open protocol that would become known as [BitTorrent](https://en.wikipedia.org/wiki/BitTorrent). | ||
| BitTorrent would immediately become popular with the Linux community, as it allowed for the free distribution of Linux distributions and other free software that would not have had the funding or labor to distribute their software otherwise. | ||
| And by 2003, [ThePirateBay](https://en.wikipedia.org/wiki/The_Pirate_Bay) would launch, becoming one of the most infamous websites in the world to download free _pirated_ content, such as music, movies, and TV shows. | ||
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| ## BitTorrent Basics | ||
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| BitTorrent decentralizes the file sharing process. | ||
| Rather than one server being required to serve a file to many users, which can become bottle necked, BitTorrent allows for many users to share files with each other by joining a "swarm". | ||
| Users within the swarm can advertise they have a file, or a part of it, and exchange "pieces" with other users in the swarm. | ||
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| ### Torrent files | ||
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| In order to distribute a file using BitTorrent, a ["torrent"](https://en.wikipedia.org/wiki/Torrent_file) file is created, which contains metadata about the file(s) to be shared. | ||
| You can use a tool such as [TorrentEditor](https://torrenteditor.com/) to view the contents of a torrent file online. Here for example is the contents of the Ubuntu 23.04 Server ISO. | ||
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| :::info | ||
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| #### Ubuntu 23.04 Live Server Torrent Details | ||
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| **Filename:** ubuntu-23.04-live-server-amd64.iso.torrent | ||
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| ##### Hash Details | ||
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| Info Hash: D6B4535B A8F2B340 12BC6335 69F113E7 7017E032 | ||
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| ##### Tracker Information | ||
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| **Tracker URL:** https://torrent.ubuntu.com/announce | ||
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| **Seeds:** 158, **Peers:** 4, **Completed:** 1 | ||
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| Additional Tracker: https://ipv6.torrent.ubuntu.com/announce | ||
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| **Seeds:** 158, **Peers:** 4 **Completed:** 1 | ||
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| ##### Metadata | ||
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| - **Created On:** 04/20/23 12:14:49 | ||
| - **Created By:** mktorrent 1.1 | ||
| - **Comment:** Ubuntu CD releases.ubuntu.com | ||
| - **Piece Length\*:** 256 KB | ||
| - **Private\*:** Off - Unset | ||
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| ##### Files | ||
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| **Filename:** ubuntu-23.04-live-server-amd64.iso | ||
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| **File Size:** 2.46 GB | ||
| ::: | ||
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| The torrent file itself is incredibly small, for this 2.46 GB ISO the torrent itself is only 200 KB. | ||
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| ### Magnet links | ||
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| The data inside a torrent file is so small, that it can, in fact be can be represented as a URL rather than a file. | ||
| A ['Magnet link'](https://en.wikipedia.org/wiki/Magnet_URI_scheme) is a URL scheme that allows you to share information about a torrent as a link, rather than a file. | ||
| This means websites that want to share torrents, no longer had to worry about serving files, making it extremely robust to simply share a _static_ webpage with links to all the files you want to share. | ||
| Static webpages are extremely easy to host, robust against traffic spikes and take-down attempts, and can often even be hosted for free on a number of services online. | ||
| This helped make torrent indexers like ThePirateBay _decentralized_. In 2012, in an effort to ensure the longevity of the content on ThePirateBay and thanks to their recent conversion to magnet links, the site was replicated by users and [reduced to a 90 MB torrent file](https://torrentfreak.com/the-pirate-bay-returns-121213/) that anyone could copy and re-host. | ||
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| A magnet link works similar to how if you have ever clicked on an email address in the browser before and had it open up your default email client. | ||
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| If you have never seen an email link before, it looks like this: | ||
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| ```html | ||
| <a href="mailto:[email protected]">[email protected]</a> | ||
| ``` | ||
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| If you click on that link, it will open up your default email client and create a new email to the address. | ||
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| Similarly, a magnet link looks like this: | ||
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| ```html | ||
| <a href="magnet:?xt=urn:btih:222FGW5I6KZUAEV4MM2WT4IT45YBPYBS&dn=ubuntu-23.04-live-server-amd64.iso&xl=2641264640&tr=https%3A%2F%2Ftorrent.ubuntu.com%2Fannounce">ubuntu-23.04-live-server-amd64.iso</a> | ||
| ``` | ||
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| This link, when clicked, will launch your system default torrent client and begin downloading the file. | ||
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| ### Torrent Clients | ||
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| If you were downloading a typical file from the internet, you would likely use a web browser to grab the file, save it to your computer and then end communication with the server. | ||
| BitTorrent is different, as it is a peer-to-peer protocol, you are not just downloading a file from a server, you are also uploading the file to other users. | ||
| To do so, you'll need a BitTorrent client, some software that can communicate with other users and share the file. | ||
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| There are many BitTorrent clients available, but the most popular these days are: | ||
| - [Transmission](https://transmissionbt.com/) | ||
| - [Deluge](https://deluge-torrent.org/) | ||
| - [qBittorrent](https://www.qbittorrent.org/) | ||
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| ### Torrent Tracker | ||
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| In order to begin downloading a file via torrent, you need to connect with other "peers" or users in the swarm who have "pieces" of the file you want. | ||
| A "[tracker](https://en.wikipedia.org/wiki/BitTorrent_tracker)" is a web server that keeps track of members in a swarm and aids in connecting users together based on which pieces of the file they have. | ||
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| When a torrent client initiates a download from a torrent file, it will first connect to the tracker and announce that it is joining the swarm and what pieces of the file it has available, if any. | ||
| The tracker will respond with a list of peers that the client can connect to and begin downloading the file from. Once the client and a peer have connected, they no longer require the tracker to communicate with each other. However, the client will continue to communicate with the tracker to update it on the pieces it has available and to receive a list of new peers to connect with. | ||
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| If a tracker were to go down before you got the chance to connect to the swarm, it might be very difficult to find other peers to connect with. You'll notice most torrent files will have multiple trackers listed to ensure longevity of the torrent. If all trackers were offline, it would still be possible to join the swarm if your client was aware of at least one other peer in the swarm. Luckily, this is where the [DHT](#dht-distributed-hash-table) comes in. | ||
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| ### DHT (Distributed Hash Table) | ||
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| A [DHT](https://en.wikipedia.org/wiki/Distributed_hash_table) is a decentralized system for storing and retrieving simple key-value data, where any member of the network retrieve data from any other member of the network. In BitTorrent, the [Mainline DHT](https://en.wikipedia.org/wiki/Mainline_DHT) protocol is used to store information about torrents and their peers locally. The DHT works as an alternative to a tracker and can aid in connecting to a swarm if the tracker is offline. | ||
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| To find peers for a particular swarm over DHT, a `get_peers` query is made with the SHA-1 hash of the torrent (the "infohash") as the key to the "nearest" node in the DHT. The node will then respond with a list of peers in the swarm. If the node does not have any peers, it will respond with a list of other nodes in the DHT that are closer to the infohash. The client will then query those nodes for peers and continue until it has found peers to connect with. An algorithmic virtual game of telephone. It is important to note that "nearest" in the context of the DHT is not related to physical geographical distance, but instead a mathematical distance that creates efficient and balanced routing. | ||
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