3.4 Upgrading packages

Package upgrades are a great success of the APT system. They can be achieved with a single command: apt-get upgrade. You can use this command to upgrade packages within the same distribution, as well as to upgrade to a new distribution, although for the latter the command apt-get dist-upgrade is preferred; see section Upgrading to a new release, Section 3.5 for more details.

It's useful to run this command with the -u option. This option causes APT to show the complete list of packages which will be upgraded. Without it, you'll be upgrading blindly. APT will download the latest versions of each package and will install them in the proper order. It's important to always run apt-get update before you try this. See section Updating the list of available packages, Section 3.1. Look at this example:

     # apt-get -u upgrade
     Reading Package Lists... Done
     Building Dependency Tree... Done
     The following packages have been kept back
       cpp gcc lilo 
     The following packages will be upgraded
       adduser ae apt autoconf debhelper dpkg-dev esound esound-common ftp indent
       ipchains isapnptools libaudiofile-dev libaudiofile0 libesd0 libesd0-dev
       libgtk1.2 libgtk1.2-dev liblockfile1 libnewt0 liborbit-dev liborbit0
       libstdc++2.10-glibc2.2 libtiff3g libtiff3g-dev modconf orbit procps psmisc 
     29 packages upgraded, 0 newly installed, 0 to remove and 3 not upgraded.
     Need to get 5055B/5055kB of archives. After unpacking 1161kB will be used.
     Do you want to continue? [Y/n]

The process is very simple. Note that in the first few lines, apt-get says that some packages were kept back. This means that there are new versions of these packages which will not be installed for some reason. Possible reasons are broken dependencies (a package on which it depends doesn't have a version available for download) or new dependencies (the package has come to depend on new packages since the last version).

There's no clean solution for this first case. For the second case, it's sufficient to run apt-get install for the specific package in question, as this will download the dependencies. An even cleaner solution is to use dist-upgrade. See section Upgrading to a new release, Section 3.5.