Edit boot entry At boot menu by press "e" to edit a boot entry, go to the line beginning with "linux".
Add "systemd.confirm_spawn=1", remove "rhgb quiet" linux16 /vmlinuz-3.10.0-123.9.3.el7.x86_64 root=/dev/mapper/ol-root ro crashkernel=auto vconsole.font=latarcyrheb-sun16 rd.lvm.lv=ol/swap rd.lvm.lv=ol/root vconsole.keymap=us rhgb quiet LANG=en_US.UTF-8 systemd.confirm_spawn=1
Continue to boot up linux
Press Ctrl-x to continue the boot process. The system will now ask interactively which services are to be started.