QEMU is a generic and open-source machine emulator and virtualizer. When used as a machine emulator, QEMU can run OSs and programs made for one machine (for example, an ARM board) on a different machine (for example, your own PC). QEMU is really its own virtualization solution that works in user space. Combining it with KVM speeds it up considerably, providing a robust hypervisor running at the kernel level.
When qemu is launched from the command line the GUI of the virtual machine does not launch but only a message.
VNC server started at 127.0.0.1:5869
appears on the terminal.
The problem most probably is because the sdl libraries have not been installed. Hence install the same using the package manager of your respective distro. For eg if you are running Debian(Ubuntu) based systems then run the following commands in the terminal.
$ sudo apt-get install libsdl1.2-dev
Now try running the qemu and GUI should appear.