Even I faced same issue with CentOS 6.5 running on a VM. I didn't observe any errors since the terminal (within VM) which I used for ./stack.sh was closed during automatic log out. Same issue repeated after fresh login. As a workaround, sshed into CentOS VM from different machine and ran stack.sh successfully.

Thanks, Shankarganesh.P.J

Does stack.sh.log file show any errors just before the system logs out? Try looking into the step that was performed last just before your system logs out. There can be a mis-configuration in the host that conflicts with the stack.sh script.