Ubuntu – “dist-upgrade” and why does it upgrade more than “upgrade”

apt

I was wondering why upgrade sometimes doesn't want to upgrade certain parts of the system, while dist-upgrade does. Here's an example after running apt-get upgrade:

apt-get upgrade:

rimmer@rimmer-Lenovo-IdeaPad-S10-2:~$ sudo apt-get upgrade
Reading package lists... Done
Building dependency tree       
Reading state information... Done
The following packages have been kept back:
  linux-generic linux-headers-generic linux-image-generic
0 upgraded, 0 newly installed, 0 to remove and 3 not upgraded.

versus apt-get dist-upgrade:

rimmer@rimmer-Lenovo-IdeaPad-S10-2:~$ sudo apt-get dist-upgrade
Reading package lists... Done
Building dependency tree       
Reading state information... Done
Calculating upgrade... Done
The following NEW packages will be installed:
  linux-headers-3.0.0-13 linux-headers-3.0.0-13-generic
  linux-image-3.0.0-13-generic
The following packages will be upgraded:
  linux-generic linux-headers-generic linux-image-generic
3 upgraded, 3 newly installed, 0 to remove and 0 not upgraded.
Need to get 48.5 MB of archives.
After this operation, 215 MB of additional disk space will be used.
Do you want to continue [Y/n]?

In other words, why can't this be performed by upgrade?

Best Answer

From apt-get manual:

upgrade
   upgrade is used to install the newest versions of all packages
   currently installed on the system from the sources enumerated in
   /etc/apt/sources.list. Packages currently installed with new
   versions available are retrieved and upgraded; under no
   circumstances are currently installed packages removed, or packages
   not already installed retrieved and installed. New versions of
   currently installed packages that cannot be upgraded without
   changing the install status of another package will be left at
   their current version. An update must be performed first so that
   apt-get knows that new versions of packages are available.

dist-upgrade
   dist-upgrade in addition to performing the function of upgrade,
   also intelligently handles changing dependencies with new versions
   of packages; apt-get has a "smart" conflict resolution system, and
   it will attempt to upgrade the most important packages at the
   expense of less important ones if necessary. So, dist-upgrade
   command may remove some packages. The /etc/apt/sources.list file
   contains a list of locations from which to retrieve desired package
   files. See also apt_preferences(5) for a mechanism for overriding
   the general settings for individual packages.

And with the newer apt tool available from 14.04 onwards:

full-upgrade
   full-upgrade performs the function of upgrade but may also remove
   installed packages if that is required in order to resolve a
   package conflict.

In your particular case, I see, for example, that linux-headers is a virtual package that is provided by both linux-headers-3.0.0-12 and linux-headers-3.0.0-13 and that sounds like the kind of package installation and removal handled by dist-upgrade, but not by upgrade.

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