What: /sys/power/ Date: August 2006 Contact: Rafael J. Wysocki 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 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: September 2006 Contact: Rafael J. Wysocki 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. Additionally, /sys/power/disk can be used to turn on one of the two testing modes of the suspend-to-disk mechanism: 'testproc' or 'test'. If the suspend-to-disk mechanism is in the 'testproc' mode, writing 'disk' to /sys/power/state will cause the kernel to disable nonboot CPUs and freeze tasks, wait for 5 seconds, unfreeze tasks and enable nonboot CPUs. If it is in the 'test' mode, writing 'disk' to /sys/power/state will cause the kernel to disable nonboot CPUs and freeze tasks, shrink memory, suspend devices, wait for 5 seconds, resume devices, unfreeze tasks and enable nonboot CPUs. Then, we are able to look in the log messages and work out, for example, which code is being slow and which device drivers are misbehaving. The suspend-to-disk method may be chosen by writing to this file one of the accepted strings: 'firmware' 'platform' 'shutdown' 'reboot' 'testproc' 'test' 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 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 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' If you do not get any matches (or they appear to be false positives), it is possible that the last PM event point referred to a device created by a loadable kernel module. In this case cat /sys/power/pm_trace_dev_match (see below) after your system is started up and the kernel modules are loaded. CAUTION: Using it will cause your machine's real-time (CMOS) clock to be set to a random invalid time after a resume. What; /sys/power/pm_trace_dev_match Date: October 2010 Contact: James Hogan Description: The /sys/power/pm_trace_dev_match file contains the name of the device associated with the last PM event point saved in the RTC across reboots when pm_trace has been used. More precisely it contains the list of current devices (including those registered by loadable kernel modules since boot) which match the device hash in the RTC at boot, with a newline after each one. The advantage of this file over the hash matches printed to the kernel log (see /sys/power/pm_trace), is that it includes devices created after boot by loadable kernel modules. Due to the small hash size necessary to fit in the RTC, it is possible that more than one device matches the hash, in which case further investigation is required to determine which device is causing the problem. Note that genuine RTC clock values (such as when pm_trace has not been used), can still match a device and output it's name here. What: /sys/power/pm_async Date: January 2009 Contact: Rafael J. Wysocki Description: The /sys/power/pm_async file controls the switch allowing the user space to enable or disable asynchronous suspend and resume of devices. If enabled, this feature will cause some device drivers' suspend and resume callbacks to be executed in parallel with each other and with the main suspend thread. It is enabled if this file contains "1", which is the default. It may be disabled by writing "0" to this file, in which case all devices will be suspended and resumed synchronously. What: /sys/power/wakeup_count Date: July 2010 Contact: Rafael J. Wysocki Description: The /sys/power/wakeup_count file allows user space to put the system into a sleep state while taking into account the concurrent arrival of wakeup events. Reading from it returns the current number of registered wakeup events and it blocks if some wakeup events are being processed at the time the file is read from. Writing to it will only succeed if the current number of wakeup events is equal to the written value and, if successful, will make the kernel abort a subsequent transition to a sleep state if any wakeup events are reported after the write has returned. What: /sys/power/reserved_size Date: May 2011 Contact: Rafael J. Wysocki Description: The /sys/power/reserved_size file allows user space to control the amount of memory reserved for allocations made by device drivers during the "device freeze" stage of hibernation. It can be written a string representing a non-negative integer that will be used as the amount of memory to reserve for allocations made by device drivers' "freeze" callbacks, in bytes. Reading from this file will display the current value, which is set to 1 MB by default.