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1What: /sys/power/
2Date: August 2006
3Contact: Rafael J. Wysocki <rjw@sisk.pl>
4Description:
5 The /sys/power directory will contain files that will
6 provide a unified interface to the power management
7 subsystem.
8
9What: /sys/power/state
10Date: August 2006
11Contact: Rafael J. Wysocki <rjw@sisk.pl>
12Description:
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
23What: /sys/power/disk
24Date: August 2006
25Contact: Rafael J. Wysocki <rjw@sisk.pl>
26Description:
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 The suspend-to-disk method may be chosen by writing to this
43 file one of the accepted strings:
44
45 'firmware'
46 'platform'
47 'shutdown'
48 'reboot'
49
50 It will only change to 'firmware' or 'platform' if the system
51 supports that.
52
53What: /sys/power/image_size
54Date: August 2006
55Contact: Rafael J. Wysocki <rjw@sisk.pl>
56Description:
57 The /sys/power/image_size file controls the size of the image
58 created by the suspend-to-disk mechanism. It can be written a
59 string representing a non-negative integer that will be used
60 as an upper limit of the image size, in bytes. The kernel's
61 suspend-to-disk code will do its best to ensure the image size
62 will not exceed this number. However, if it turns out to be
63 impossible, the kernel will try to suspend anyway using the
64 smallest image possible. In particular, if "0" is written to
65 this file, the suspend image will be as small as possible.
66
67 Reading from this file will display the current image size
68 limit, which is set to 500 MB by default.
69
70What: /sys/power/pm_trace
71Date: August 2006
72Contact: Rafael J. Wysocki <rjw@sisk.pl>
73Description:
74 The /sys/power/pm_trace file controls the code which saves the
75 last PM event point in the RTC across reboots, so that you can
76 debug a machine that just hangs during suspend (or more
77 commonly, during resume). Namely, the RTC is only used to save
78 the last PM event point if this file contains '1'. Initially
79 it contains '0' which may be changed to '1' by writing a
80 string representing a nonzero integer into it.
81
82 To use this debugging feature you should attempt to suspend
83 the machine, then reboot it and run
84
85 dmesg -s 1000000 | grep 'hash matches'
86
87 CAUTION: Using it will cause your machine's real-time (CMOS)
88 clock to be set to a random invalid time after a resume.