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The Linux power management subsystem shows a unified sysfs interface to userspace. The interface exists in /sys/power/ directory.
The file: /sys/power/state controls the system power state. A reading from this file, will return what states are supported, which are hard-coded to:
  • standby (Power-On Suspend),
  • mem (Power-On Suspend-to-RAM)
  • disk (Power-Off Suspend-to-Disk)

To add the standby and suspend on memory support in the kernel it is necessary to enable: 
 Power management option ---> Power management support
 Power management option ---> Suspend to RAM and standby

To enter in standby type on the available target: 
 target# echo -n standby > /sys/pm/state

To enter in suspend on memory type on the available target: 
   target# echo -n mem > /sys/pm/state


Bibliography
  • Linux Symposium 2002: The Linux Kernel Device Model
  • Linux Symposium 2003: Linux Kernel Power Management
  • Linux Symposium 2005: The sysfs Filesystem
  • Linux Symposium 2008: Suspend-to-RAM in Linux
  • Linux Kernel Weekly: A new suspend/hibernate infrastructure