Using Fish as default shell crashes KDE

[Lily White]

When I use fish as the default shell (via chsh). After a system reboot, 
The KDE login screen would show up, but after logging in, it displays 
only a blank screen.

I quit X to look at the logs and saw core dumps left and right. 
Moreover, some commands like `reboot' and even `init' are not found by 
the shell (both fish and bash), and it even thinks I need to install the 
`systemd' package. Though `systemctl' is still available.

My guess is that the booting KDE requires running something in my profiles.

Any explanations?