Based on kernel version 2.6.26. Page generated on 2008-07-16 21:12 EST.
1 What: /sys/power/ 2 Date: August 2006 3 Contact: Rafael J. Wysocki <rjw[AT]sisk[DOT]pl> 4 Description: 5 The /sys/power directory will contain files that will 6 provide a unified interface to the power management 7 subsystem. 8 9 What: /sys/power/state 10 Date: August 2006 11 Contact: Rafael J. Wysocki <rjw[AT]sisk[DOT]pl> 12 Description: 13 The /sys/power/state file controls the system power state. 14 Reading from this file returns what states are supported, 15 which is hard-coded to 'standby' (Power-On Suspend), 'mem' 16 (Suspend-to-RAM), and 'disk' (Suspend-to-Disk). 17 18 Writing to this file one of these strings causes the system to 19 transition into that state. Please see the file 20 Documentation/power/states.txt for a description of each of 21 these states. 22 23 What: /sys/power/disk 24 Date: September 2006 25 Contact: Rafael J. Wysocki <rjw[AT]sisk[DOT]pl> 26 Description: 27 The /sys/power/disk file controls the operating mode of the 28 suspend-to-disk mechanism. Reading from this file returns 29 the name of the method by which the system will be put to 30 sleep on the next suspend. There are four methods supported: 31 'firmware' - means that the memory image will be saved to disk 32 by some firmware, in which case we also assume that the 33 firmware will handle the system suspend. 34 'platform' - the memory image will be saved by the kernel and 35 the system will be put to sleep by the platform driver (e.g. 36 ACPI or other PM registers). 37 'shutdown' - the memory image will be saved by the kernel and 38 the system will be powered off. 39 'reboot' - the memory image will be saved by the kernel and 40 the system will be rebooted. 41 42 Additionally, /sys/power/disk can be used to turn on one of the 43 two testing modes of the suspend-to-disk mechanism: 'testproc' 44 or 'test'. If the suspend-to-disk mechanism is in the 45 'testproc' mode, writing 'disk' to /sys/power/state will cause 46 the kernel to disable nonboot CPUs and freeze tasks, wait for 5 47 seconds, unfreeze tasks and enable nonboot CPUs. If it is in 48 the 'test' mode, writing 'disk' to /sys/power/state will cause 49 the kernel to disable nonboot CPUs and freeze tasks, shrink 50 memory, suspend devices, wait for 5 seconds, resume devices, 51 unfreeze tasks and enable nonboot CPUs. Then, we are able to 52 look in the log messages and work out, for example, which code 53 is being slow and which device drivers are misbehaving. 54 55 The suspend-to-disk method may be chosen by writing to this 56 file one of the accepted strings: 57 58 'firmware' 59 'platform' 60 'shutdown' 61 'reboot' 62 'testproc' 63 'test' 64 65 It will only change to 'firmware' or 'platform' if the system 66 supports that. 67 68 What: /sys/power/image_size 69 Date: August 2006 70 Contact: Rafael J. Wysocki <rjw[AT]sisk[DOT]pl> 71 Description: 72 The /sys/power/image_size file controls the size of the image 73 created by the suspend-to-disk mechanism. It can be written a 74 string representing a non-negative integer that will be used 75 as an upper limit of the image size, in bytes. The kernel's 76 suspend-to-disk code will do its best to ensure the image size 77 will not exceed this number. However, if it turns out to be 78 impossible, the kernel will try to suspend anyway using the 79 smallest image possible. In particular, if "0" is written to 80 this file, the suspend image will be as small as possible. 81 82 Reading from this file will display the current image size 83 limit, which is set to 500 MB by default. 84 85 What: /sys/power/pm_trace 86 Date: August 2006 87 Contact: Rafael J. Wysocki <rjw[AT]sisk[DOT]pl> 88 Description: 89 The /sys/power/pm_trace file controls the code which saves the 90 last PM event point in the RTC across reboots, so that you can 91 debug a machine that just hangs during suspend (or more 92 commonly, during resume). Namely, the RTC is only used to save 93 the last PM event point if this file contains '1'. Initially 94 it contains '0' which may be changed to '1' by writing a 95 string representing a nonzero integer into it. 96 97 To use this debugging feature you should attempt to suspend 98 the machine, then reboot it and run 99 100 dmesg -s 1000000 | grep 'hash matches' 101 102 CAUTION: Using it will cause your machine's real-time (CMOS) 103 clock to be set to a random invalid time after a resume.