Ever so often, you might try to update your Ubuntu Server packages and find that certain ones are “kept back” during the upgrade process. These will often be kernel or other mission critical packages that do not get updated.
The reason some packages might get kept back is that some dependencies have been changed for them, and installing the new versions will require additional packages to be installed. In most cases, the new installations will not hurt your system, but those packages are still held so that you can manually review each case.
Fortunately, the fix for this problem is quite simple. If you have run “upgrade”, and some packages are kept back, all you have to do to install them is run “dist-upgrade”. This will make sure your entire distribution is up to date and will install those “kept back” packages along with their new dependencies.
From the command line type:
$ sudo apt-get dist-upgrade
Alternatively, if you are unsure if you want to upgrade the entire system, you can install each package individually and approve any new dependencies as you are prompted. For more information as well as a lengthy discussion about the topic, see the Debian administration page.