When using the installer (bin) to upgrade Confluence on Linux, the installer does not keep the port number from the older version, setting it to the default 8090 again.

Documentation says:

During the upgrade the wizard will migrate following from your existing Confluence installation:

TCP port values in your server.xml file.

Steps to reproduce

1. Install a Confluence 5.0.3, for example
2. Modify its port number on <confluence-install-folder>/conf/server.xml to use 8099, for example.
3. Download Confluence 5.6.4 bin installer for Linux
4. Run it and select the Upgrade option, pointing it to the 5.0.3 version you've just installed.
5. Once the upgrade is done, the installer prints a message like the following one:
   Confluence 5.6.4 can be accessed at http://localhost:8099
   • However, if we check its server.xml file under <confluence-install-folder>/conf/server.xml, we'll see that the port number got updated to 8090 instead of keeping the 8099 one.

Workaround

Stop the Confluence instance and set the port number on <confluence-install-folder>/conf/server.xml again.