Why do cdimage.ubuntu.com and releases.ubuntu.com list different images?

There are two places I go when I want to download Ubuntu installer images: cdimage.ubuntu.com and releases.ubuntu.com.

Both of these appear equally official: they are both subdomains of ubuntu.com, and the main Ubuntu website makes references to both for its download links. (http://www.ubuntu.com/download/alternative-downloads uses the former for its 'Network installer' download links, and the latter for its 'BitTorrent' download links, for example.)

If I visit http://releases.ubuntu.com/ and follow links for the current Ubuntu release, I reach a page that lists numerous links to desktop and server installer images. Likewise, if I visit http://cdimage.ubuntu.com/ and follow links in a similar manner, I get to another very similar page that also gives numerous links to desktop and server installer images. At the moment, these pages are:

• http://releases.ubuntu.com/trusty/
• http://cdimage.ubuntu.com/releases/trusty/release/

(Following '14.04' links instead of 'trusty' leads to pages identical to the above, aside from their URLs.)

The language used on those two pages suggests that each page lists all of the available image files. For example, they each say "A full list of available files, including BitTorrent files, can be found below", and they each provide a wide variety of link types (.iso, .torrent, .metalink etc).

Neither page makes any reference to the other page's existence, and for a long time I thought that these were simply two different URLs serving essentially the same list of installer images.

Right?

Now that I look more closely I see that, despite appearances, the actual lists of files are almost entirely different. For the Trusty release, releases serves i386 and amd64 images, whilst the cdimage site serves PowerPC and Mac-friendly images. Even going back to the Precise release, when the architectures overlapped more, there are still installer images on each page that are not available from the other.

I've searched for explanations as to why the two sites are so disjoint, but have so far found none.

I assume that releases.ubuntu.com is intended to hold the more common installer images, whilst cdimage.ubuntu.com is intended to be a more comprehensive archive, given that it also hosts installers for the various spins such as Lubuntu, Xubuntu, etc.

However, this still doesn't explain some things:

• Why is there no single page I can go to and see all available images? For example, if releases.ubuntu.com is reserved for the more popular images, why are these not also included in the (more comprehensive) list at cdimage.ubuntu.com?

• If there's a good reason for keeping them separate, then why does neither page acknowledge the other as a complementary source of installer images?

• Is there any historical reason for this split?

If anyone has any behind-the-scenes insight into this, I'd be interested to hear how things ended up this way.

Solution 1:

The 1st page of releases.ubuntu.com seems to me to explain why:

Ubuntu Releases

The following releases of Ubuntu are available:

• Ubuntu 14.10 (Utopic Unicorn)
• Ubuntu 14.04.1 LTS (Trusty Tahr)
• Ubuntu 13.10 (Saucy Salamander)
• Ubuntu 13.04 (Raring Ringtail)
• Ubuntu 12.10 (Quantal Quetzal)
• Ubuntu 12.04.5 LTS (Precise Pangolin)
• Ubuntu 10.04.4 LTS (Lucid Lynx)

We are happy to provide hosting for the following projects via the cdimage server. While they are not commercially supported by Canonical, they receive full support from their communities.

• Edubuntu
• Kubuntu
• Lubuntu
• Mythbuntu
• Ubuntu GNOME
• UbuntuKylin
• UbuntuStudio
• Xubuntu

The cdimage server also hosts releases of other Ubuntu images not found on this server, such as builds for less popular architectures and other non-standard and unsupported images. For Ubuntu Desktop and Server on popular architectures, please see the links above instead.

• Unsupported Ubuntu Images

For old releases, see old-releases.ubuntu.com.

• releases.ubuntu.com

  Contains only current commercially supported releases images (i386 & amd64 only, 5 years period max LTS for server editions).

• old-releases.ubuntu.com/releases/

  Old releases images that no longer supported.

• cdimage.ubuntu.com/releases/

  Commercially unsupported favors and builds including alpha, beta and daily builds.

• cloud-images.ubuntu.com, old sub-domain is still working too uec-images.ubuntu.com

  Ubuntu Cloud Images are pre-installed disk images that have been customized by Ubuntu engineering to run on cloud-platforms such as Amazon EC2, Openstack, Windows and LXC.

  It was there in 2010 as shown in the history of UEC/Images Wiki page, Revision 2 as of 2010-08-19 20:59:56.

As canonical is a company that provides technical support, it should have should have such kind of separation.

Looking to the official links on www.ubuntu.com. They are all point to releases.ubuntu.com except Network installer and Ubuntu Kylin.

Another thing, they always try to minimize mirror size and mirroring daily builds just wasting of resources. Mirror script point only to releases.ubuntu.com

I couldn't find out any official note about such decision yet. But separation between releases and other builds back to 2005 at least. See Ubuntu Server Project Unleashed!. Even back to Oct 2004 with release of Ubuntu 4.10 which is the first release(just i386), Make a look on these few early mails from ubuntu-announce archive.

Solution 2:

As you pointed out, release.ubuntu.com is intended to hold more common installer image, whereas cdimage.ubuntu.com is for other images, like PowerPC or Kubuntu.

In my opinion, Canonical intended to split installers based on their popularity, since Ubuntu installer images are usually distributed using mirrors. Operators of mirror services can choose what type of mirror they want to copy.

For example, http://mirror.csclub.uwaterloo.ca/ubuntu-releases/ (Ubuntu mirror "University of Waterloo Computer Science Club") has images of releases.ubuntu.com and there is a link for cdimage server.