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- What: /sys/power/
- Date: August 2006
- Contact: Rafael J. Wysocki <rjw@sisk.pl>
- Description:
- The /sys/power directory will contain files that will
- provide a unified interface to the power management
- subsystem.
- What: /sys/power/state
- Date: August 2006
- Contact: Rafael J. Wysocki <rjw@sisk.pl>
- Description:
- The /sys/power/state file controls the 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 these strings causes the system to
- transition into that state. Please see the file
- Documentation/power/states.txt for a description of each of
- these states.
- What: /sys/power/disk
- Date: August 2006
- Contact: Rafael J. Wysocki <rjw@sisk.pl>
- Description:
- The /sys/power/disk file controls the operating mode of the
- suspend-to-disk mechanism. Reading from this file returns
- the name of the method by which the system will be put to
- sleep on the next suspend. There are four methods supported:
- 'firmware' - means that the memory image will be saved to disk
- by some firmware, in which case we also assume that the
- firmware will handle the system suspend.
- 'platform' - the memory image will be saved by the kernel and
- the system will be put to sleep by the platform driver (e.g.
- ACPI or other PM registers).
- 'shutdown' - the memory image will be saved by the kernel and
- the system will be powered off.
- 'reboot' - the memory image will be saved by the kernel and
- the system will be rebooted.
- The suspend-to-disk method may be chosen by writing to this
- file one of the accepted strings:
- 'firmware'
- 'platform'
- 'shutdown'
- 'reboot'
- It will only change to 'firmware' or 'platform' if the system
- supports that.
- What: /sys/power/image_size
- Date: August 2006
- Contact: Rafael J. Wysocki <rjw@sisk.pl>
- Description:
- The /sys/power/image_size file 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 kernel's
- suspend-to-disk code will do its best to ensure the image size
- will not exceed this number. However, if it turns out to be
- impossible, the kernel 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.
- What: /sys/power/pm_trace
- Date: August 2006
- Contact: Rafael J. Wysocki <rjw@sisk.pl>
- Description:
- The /sys/power/pm_trace file controls the code which saves the
- last PM event point in the RTC across reboots, so that you can
- debug a machine that just hangs during suspend (or more
- commonly, during resume). Namely, the RTC is only used to save
- the last PM event point if this file contains '1'. Initially
- it contains '0' which may be changed to '1' by writing a
- string representing a nonzero integer into it.
- To use this debugging feature you should attempt to suspend
- the machine, then reboot it and run
- dmesg -s 1000000 | grep 'hash matches'
- CAUTION: Using it will cause your machine's real-time (CMOS)
- clock to be set to a random invalid time after a resume.
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