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- Power Management Interface
- The power management subsystem provides a unified sysfs interface to
- userspace, regardless of what architecture or platform one is
- running. The interface exists in /sys/power/ directory (assuming sysfs
- is mounted at /sys).
- /sys/power/state controls system power state. Reading from this file
- returns what states are supported, which is hard-coded to 'standby'
- (Power-On Suspend), 'mem' (Suspend-to-RAM), and 'disk'
- (Suspend-to-Disk).
- Writing to this file one of those strings causes the system to
- transition into that state. Please see the file
- Documentation/power/states.txt for a description of each of those
- states.
- /sys/power/disk controls the operating mode of the suspend-to-disk
- mechanism. Suspend-to-disk can be handled in several ways. The
- greatest distinction is who writes memory to disk - the firmware or
- the kernel. If the firmware does it, we assume that it also handles
- suspending the system.
- If the kernel does it, then we have three options for putting the system
- to sleep - using the platform driver (e.g. ACPI or other PM
- registers), powering off the system or rebooting the system (for
- testing). The system will support either 'firmware' or 'platform', and
- that is known a priori. But, the user may choose 'shutdown' or
- 'reboot' as alternatives.
- Reading from this file will display what the mode is currently set
- to. Writing to this file will accept one of
- 'firmware'
- 'platform'
- 'shutdown'
- 'reboot'
- It will only change to 'firmware' or 'platform' if the system supports
- it.
- /sys/power/image_size controls the size of the image created by
- the suspend-to-disk mechanism. It can be written a string
- representing a non-negative integer that will be used as an upper
- limit of the image size, in bytes. The suspend-to-disk mechanism will
- do its best to ensure the image size will not exceed that number. However,
- if this turns out to be impossible, it will try to suspend anyway using the
- smallest image possible. In particular, if "0" is written to this file, the
- suspend image will be as small as possible.
- Reading from this file will display the current image size limit, which
- is set to 500 MB by default.
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