Managing different versions of a software - update-alternatives

Managing different versions of a software in Ubuntu is made easy by update-alternatives. For example, assume having different versions of eclipse in Ubuntu.

The eclipse can be installed from the tar balls available from eclipse download page. Juno Download page. Indigo Download Page.

Move the downloaded the tar balls to /opt and unzip them. (/opt - just a directory for optional packages)

$cd /opt
/opt$sudo mv ~/Downloads/eclipse-cpp-juno-SR2-linux-gtk-x86_64.tar.gz .
/opt$sudo tar xzvf eclipse-cpp-juno-SR2-linux-gtk-x86_64.tar.gz
/opt$sudo mv eclipse eclipse_juno
/opt$sudo mv ~/Downloads/eclipse-cpp-indigo-SR2-incubation-linux-gtk-x86_64.tar.gz .
/opt$sudo tar xzvf eclipse-cpp-indigo-SR2-incubation-linux-gtk-x86_64.tar.gz
/opt$sudo mv eclipse eclipse_indigo

The launcher executable (eclipse.exe) for the installed versions of eclipse would be in the respective install folder. I.e., In our case there will be a launcher executable (eclipse.exe) inside "/opt/eclipse_juno/" and "/opt/eclipse_indigo".

Now to manage the launch of these two versions of eclipse, we use the "update-alternatives" as shown below.

$sudo update-alternatives --install /usr/bin/eclipse eclipse /opt/eclipse_juno/eclipse 20
$sudo update-alternatives --install /usr/bin/eclipse eclipse /opt/eclipse_indigo/eclipse 10

Now to choose between versions, use "update-alternatives --config".

$ sudo update-alternatives --config eclipse
There are 2 choices for the alternative eclipse (providing /usr/bin/eclipse).

Selection Path                        Priority  Status
------------------------------------------------------------
* 0       /opt/eclipse_juno/eclipse   20        auto mode
  1       /opt/eclipse_indigo/eclipse 10        manual mode
  2       /opt/eclipse_juno/eclipse   20        manual mode

Press enter to keep the current choice[*], or type selection number:

By giving the selection number, the desired version shall be made set for launching.

Now we see the "update-alternatives --install" in detail. Consider the following command we issued above.

$sudo update-alternatives --install /usr/bin/eclipse eclipse /opt/eclipse_juno/eclipse 20

Here the number '20' is the priority for the version of the launcher we configure for alternatives. Higher the number higher the priority.

'/opt/eclipse_juno/eclipse' is the launcher we configure for alternatives.

'eclipse' is a symbolic link to be created in /etc/alternatives/. This symbolic link will point to the launcher we configure. Here it will be '/opt/eclipse_juno/eclipse'.

'/usr/bin/eclipse' is a symbolic link to '/etc/alternatives/eclipse'.

How it works?

'/usr/bin/eclipse' will always link to '/etc/alternatives/eclipse'. And '/etc/alternatives/eclipse' will change its link to the launcher we configure through "update-alternatives --config".