The longrun utility requires the Linux CPUID and MSR devices be compiled into the kernel, or the msr and cpuid modules must be loaded. You should use kernel 2.4.0 or later. This package includes integration with the apm and acpid daemons. To make your laptop enter low power mode when unplugged from AC power, or when the battery is low, edit /etc/default/longrun. This is disabled by default. -- Joey Hess