There are a few ways to make this happen, the simplest way is to reboot the machine with this command:

shutdown -rf now

Specifically for Debian you can also do this:

touch /fastboot

The bit more complicated way is to add fastboot as kernel parameter. This can be either done by editing it live when the server boots up or by changing your grub config /boot/grub/grub.conf. Search for menuentry and look for the part "linux" and add fastboot like in this example:

linux /boot/vmlinuz-2.6.32-5-amd64 root=UUID=6ba7e075-d8cf-4839-xxxx ro  quiet fastboot