How to manage different versions of same software in Linux?

Question

Under Ubuntu most software is available in Ubuntu repositories. What happens if I install a newer version of software from different ppa that is not available in repositories yet?

1. Will it upgrade the old version to the new one? In this case I have no fallback if the new version is faulty. What happens if Ubuntu repositories publishes an update itself later?

2. Will it install a second (new-)version in parallel? If this is the case how do I control which version I launch when I type in the program name on command line?

(To be specific: The software "Arduino 1.06" is offered via Ubuntu repositories. There is a new version 1.6 available, but not in the Ubuntu repositories yet. What happens to my old version when I install 1.6?)

Answer 1

Yes, if you install a new version of a package using Ubuntu's installation tools (Ubuntu Software Center, or a low-level tool like dpkg), it will replace the old version.

There is no no simple, supported way to install two versions of a single package in parallel. However, if there is a problem with the new version, you can go back to the old version by re-installing it.

There are some options of installing multiple versions of a program in parallel:

• Some software is packaged specially to allow this. Different versions use different package names, so they appear as different packages to the installation system, and can be installed in parallel. However, note that this only works if this is taken into account when creating the packages - you cannot just rename the packages before installation. This is most often done with libraries that have incompatible changes (for example, GTK+ V3 is packaged as libgtk-3-0, V2 as libgtk2.0-0 ).
• Get a version of the software that is not a Debian package (Ubuntu's package format), but can be installed by just unpacking it in a folder. Then you can install as many versions as you want. For example, Firefox is distributed like this.
• Finally, you can manually unpack a Debian package, install it into a folder and modify the software to find its files in the new location. This, however, can be quite complicated, so is usually only an option for software developers.