I tried to build KDE Frameworks 5 from scratch and installed in /opt/kf5. I started KDE and got this message: "All shell packages are missing.". I noticed that it was looking for a directory named plasma/shells. This directory is present in $KF5_PREFIX/share in my installation. What do I need to do to get it to start ? I included the output from startx, some error messages in there may explain why ? https://paste.kde.org/pwpp8von6

Probably the most knowledgeable guy I know of when it comes to Slackware and KDE 5 is Alien Bob, who kindly maintains a blog on the subject as well as building and maintaining most of the KDE packages for the Slackware Distro. - to include KDE 5

So in answer to your actual question, I'd guess your KDE shell directory is not in your $PATH.

In answer to the question you didn't ask, how can I just get this thing started and use it, take a look the links and follow Aliens directions for configuration and installation. Download and use Aliens packages rather than doing a config/make/make install on the sources and if my own experience is any guide, It will work like a charm as soon as you install it.

Well, among the first lines of your log there's this:

/opt/kf5/bin/startkde: line 152: kapplymousetheme: command not found

This can either mean that your plasma installation is incomplete or $KF5_PREFIX/bin (in this case /opt/kf5/bin) is not in your PATH.

Further below, I found:

27: module "org.kde.kquickcontrolsaddons" is not installed

This could mean incorrect "kdeclarative" installation, wrong QML_IMPORT_PATH or QML2_IMPORT_PATH or simply wrong cmake commands used when installing kdeclarative, and as such QML components have ended in wrong place.

klauncher said: Could not find the 'kf5/kio/trash' plugin.

This could mean similar to the above. But, this time something may be wrong with either kio or kio-extras install. You can use find . -name "*kio_trash*" in /opt/kf5 to see if it's installed in a place that's not in QT_PLUGIN_PATH

kscreen: Launcher failed to load any backend: KScreen will be useless

Similar to the problem above. libkscreen is the package you should look for. Also, search for KSC_XRandR11.so or KSC_XRandR.so. Should be in QT_PLUGIN_PATH.

See also:

http://anduin.linuxfromscratch.org/~...iles/kde5.html