This guide assumes that you have a brand-new Debian VPS from Vultr, using root. If you aren't logged in as root, type:
su -
... then enter your root password. You will be logged into the root account.
Openfire is an XMPP server program developed by Ignite Realtime. It has advanced features such as a web control panel and plugin support.
Openfire is a Java applet, and requires it to run. You can find out how to install Java in this Vultr Doc.
Openfire Debian packages can be downloaded from the official website by copying the link address of the .deb package. Once you have the address, you can use wget to download it to your VPS.
wget -O openfire.deb http://your.copied.link/
At the time of writing, the command in full would look like this:
wget -O openfire.deb http://www.igniterealtime.org/downloads/download-landing.jsp?file=openfire/openfire_3.10.0_all.deb
To install, run the following dpkg command.
dpkg --install openfire.deb
Openfire will now be installed and started as a service.
To finish the installation, you must go through the setup wizard in the web panel. To access the panel, go to http://your.ip:9090/ and follow the setup wizard.
You may need to enable other firewall ports depending on your specific needs or plugins. Check the list of ports in the admin console in System Information.
And that's it! Openfire is now installed and running on your VPS. Anyone with a configured XMPP client can connect via your IP.