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Torrent files are increasingly being replaced by magnet links, "mini torrent files" in concise and plain-text form that can be simply copy pasted around. Those link to the actual .torrent file "in the BitTorrent cloud", without relying on servers that may be temporarily overtaxed ("OMG NEW UBUNTU MUST GET NOW") or simply offline.

Does Canonical offer magnet links for their Torrent distributions? Where can one find them?

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The literal answer is that Ubuntu doesn't list its torrents as magnet links.

However they do offer something very close: http://torrent.ubuntu.com:6969/ lists all of their torrent's info hashes, which is the main piece of information a magnet link contains. If you paste one into Transmission's "Add URL" entry, Transmission will add it and start looking for peers via DHT, just as it would a magnet link.

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Canonical makes the .torrent file for the various ISO install images available for download. You can download the .torrent file for an install image, as well as various other download meta-files and the actual ISO images files, on the Ubuntu Releases page organized by release.

For example, here is the link for the page of the most frequently downloaded files for Ubuntu 12.04 LTS. The first line of a "most frequently downloaded" page for a release also contains a link to the list of download mirrors and a link to a page where you can download other images, including DVDs and source CDs.

I personally have not seen a magnet link for an Ubuntu ISO image torrent on a Canonical site. I think they don't bother with them since it is debatable whether doing so would result in a meaningful (i.e. noticeable) performance improvement.

The .torrent files for the Ubuntu ISOs tend to be quite small. Typical .torrent files sizes appear to be well under 40 KB for a CD ISO and under 100 KB for a DVD ISO. This is roughly the size of a small to medium sized image file. It is highly unlikely that the Canonical servers will be overtaxed by downloads of these files.

A more likely problem is that the servers hosting the web pages containing the download links for the .torrent files will be hard to access on high volume days. I don't see how adding magnet links could help with that. One would still have to access the (overtaxed) Canonical server hosting the web page which contained the magnet link to use the magnet link.

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Actually magnet links are slower: performance is not the point. They are more reliable however. A magnet link could conceivably simply be shared via twitter or other out-of-band mechanisms, given how relatively short they are. But I wasn't asking why doesn't Canonical give magnet links: that should've been a bug report, not a question. I was asking if and where they were published. –  badp Jun 10 '12 at 12:44
    
@badp Reliability, or more properly availability, does not strike me as something Canonical could effectively address with magnet links. As for distribution via an out-of-band mechanism, you would then have potential validation problems. How do you know that the magnet you used downloaded Canonical's Ubuntu and not a "fake Ubuntu" fabricated by some other malicious party? Of course, you can always validate an ISO by going to the Canonical site and obtaining the checksums for it. But if you're going to do that then what benefit did using the magnet provide vs downloading the .torrent itself? –  irrational John Jun 10 '12 at 12:54
    
I'd know because Marco Ceppi shared it. Or Canonical itself. Webs of trust and all that junk. But we're getting side-tracked here. –  badp Jun 10 '12 at 13:03
    
@badp Yes, it is a digression. But can you see that Canonical might have different priorities when deciding how their content is distributed than, say, a torrent index site? FWIW, if you want to tweet a magnet link for an Ubuntu release you can already do that now. All you need to do is download the torrent, extract the BTIH (BitTorrent Info Hash), and construct the magnet link. –  irrational John Jun 10 '12 at 13:15
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