Ubuntu – Are apt-get repositories hardcoded to a specific release

accessibilityaptmaintenanceusability

From the usability point of view, I do not understand why on each release upgrade you have to manually patch all the URLs of apt in order to make them point to the newer distribution.

Why is not possible for apt to auto-detect the current and use it, so when you upgrade there is no need to upgrade the urls anymore?

Best Answer

I do not understand why on each release upgrade you have to manually patch all the URLs of apt in order to make them point to the newer distribution.

You do not have to do this. (Not typically, anyway.) Actually, in Ubuntu, manually changing release names in sources.list is not a supported way to upgrade, and may often not work.

When the package manager checks to see what package versions are available to be installed or upgraded to, /etc/apt/sources.list and any configuration files in /etc/apt/sources.list.d are consulted to discover which software sources are configured. This includes but is not limited to information about what release is installed, and occasionally (though not usually!) it even makes sense to have software sources configured for releases other than the one you are running.

When you upgrade to a newer Ubuntu release using a supported method (such as the Software Updater / Update Manager or the do-release-upgrade command), the release names in sources.list are changed automatically. Some software sources, such as PPAs, may instead be disabled.

One of the reasons Ubuntu's package manager doesn't just check which release is installed and use that information dynamically to determine what software sources to use, is that there is no one thing that is the release you are running. Normally, which Ubuntu release you're using (e.g., 14.04) is well defined. But during a release upgrade, and under some other circumstances (some pathological and others proper), you may have a mixture of different releases.

In order for Ubuntu to get the point in a release upgrade where you are really, truly, and definitively running the next release (i.e., the release upgrade target), or even to the point where commonly used indicators like the contents of /etc/lsb-release would indicate the target release, it must first change what software sources are configured (to those of the target release) and upgrade, install, and remove packages to reflect what is provided by those software sources.

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Ubuntu – Does apt-get automatically check digital signatures

You are trusting that canonical compiled the program so it did not have any tampering that is not evident in the source code, and that they verified the signature on the source code from the ubuntu developer that uploaded it, or that debian did the same for the debian developer who uploaded it, if the package came from debian. You are trusting the developer who uploaded the source package, who of course, can not thoroughly review all of the upstream code, so you are also trusting all of the upstream open source contributors.

Ubuntu – How does APT work (apt-get, cache, search)

You are right that apt-get update reads from the sources (online) and the other commands apt-get search and apt-get install read from the cached information. From man apt:

update (apt-get(8))
       update is used to download package information from all configured
       sources. Other commands operate on this data to e.g. perform
       package upgrades or search in and display details about all
       packages available for installation.

The difference between apt search <package> and apt-cache search <package> is that the output of apt search is fancier (has colours, alphabetically organised, has nice line separation for easy reading) because apt is a fancy new interface. This is explained well in this answer on the difference between apt & apt-get

However, search isn't the only thing you can do with apt-cache:

Usage: apt-cache [options] command
       apt-cache [options] show pkg1 [pkg2 ...]

apt-cache queries and displays available information about installed
and installable packages. It works exclusively on the data acquired
into the local cache via the 'update' command of e.g. apt-get. The
displayed information may therefore be outdated if the last update was
too long ago, but in exchange apt-cache works independently of the
availability of the configured sources (e.g. offline).

Most used commands:
  showsrc - Show source records
  search - Search the package list for a regex pattern
  depends - Show raw dependency information for a package
  rdepends - Show reverse dependency information for a package
  show - Show a readable record for the package
  pkgnames - List the names of all packages in the system
  policy - Show policy settings

This is from the info page for apt-cache

apt combines commands from apt-get and apt-cache, so you can get the same or slightly fancier/tidied up output from any of the apt-cache [option] <package> commands with apt [option] <package> eg

apt show gimp

displays almost exactly the same as

apt-cache show gimp

Best Answer

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