Setting the Environment to Run Your Desktop
Assuming you are using a dedicated user to build , and you already have an installed version, running your new may be a bit tricky, as the new has to take precedence over the old. You must change the environment variables of your login scripts to make sure the newly-built desktop is used.

Automatically installing a login driver
Starting from version 1.16, will try to install an appropriate login driver, that will allow you to login to your -built desktop from your login manager. This can be disabled by using the install-session-driver configuration file option.
Session setup does not occur while is running in pretend mode.
This driver works by setting up a custom xsession session type. This type of session should work by default with the sddm login manager (where it appears as a Custom session), but other login managers (such as LightDM and gdm) may require additional files installed to enable xsession support.

Adding xsession support for distributions
The default login managers for some distributions may require additional packages to be installed in order to support xsession logins.
The Fedora distribution requires the xorg-x11-xinit-session package to be installed for custom xsession login support.
Debian and Debian-derived distributions should support custom xsession logins, but require the allow-user-xsession option to be set in /etc/X11/Xsession.options. See also the Debian documentation on customizing the X session.
For other distributions, go to Manually adding support for xsession.

Manually adding support for xsession
If there were no distribution-specific directions for your distribution in Adding xsession support for distributions, you can manually add a Custom xsession login entry to your distribution's list of session types as follows:

Adding an .xsession login session type.
This procedure will likely require administrative privileges to complete.
Create the file /usr/share/xsessions/kdesrc-build.desktop.
Ensure the file just created has the following text:

Type=XSession
Exec=$HOME/.xsession
Name=KDE Plasma Desktop (unstable; kdesrc-build)

The $HOME entry must be replaced by the full path to your home directory (example, /home/user). The desktop entry specification does not allow for user-generic files.
When the login manager is restarted, it should show a new session type, KDE Plasma Desktop (unstable; kdesrc-build) in its list of sessions, which should try to run the .xsession file installed by if it is selected when you login.
It may be easiest to restart the computer to restart the login manager, if the login manager does not track updates to the /usr/share/xsessions directory.

Setting up the environment manually
This documentation used to include instruction on which environment variables to set in order to load up the newly-built desktop. These instructions have been moved to an appendix ().
If you intend to setup your own login support you can consult that appendix or view the kde-env-master.sh.in file included with the source.