Difference between revisions of "Suspend to RAM"

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[[Category:Power management]]
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#REDIRECT [[Suspend and Hibernate]]
{{Article summary start}}
 
{{Article summary text|Describes the operation of the pm-utils suspend framework and supported backend methods}}
 
{{Article summary heading|Related}}
 
{{Article summary wiki|Pm-utils}}
 
{{Article summary wiki|Uswsusp}}
 
{{Article summary wiki|TuxOnIce}}
 
{{Article summary end}}
 
From [[Wikipedia:Sleep mode]]:
 
:''Sleep mode can go by many different names, including '''Stand By''', '''Sleep''', and '''Suspend'''. When placed in this sleep mode, aside from the RAM which is required to restore the machine's state, the computer attempts to cut power to all unneeded parts of the machine. Because of the large power savings, most laptops automatically enter this mode when the computer is running on batteries and the lid is closed.''
 
 
 
There is a variety of mechanisms to enable your operating system to suspend to memory or to disk. To understand the difference between these systems, you need to know that there exists a suspend/resume implementation in the kernel (swsusp) and typically a set of additional tweaks to handle specific drivers/modules/hardware (e.g. video card re-initialization).
 
 
 
* [[systemd]] provides commands for suspend to RAM, hibernate and a hybrid suspend using the kernel's native suspend/resume functionality. There are also mechanisms to add hooks to customize pre- and post-suspend actions.
 
 
 
* [[pm-utils]] is a set of shell scripts that encapsulate the kernel's suspend/resume functionality. It comes with a set of pre- and post-suspend tweaks and various hooks to customize the process.
 
 
 
* [[uswsusp]] also aims to provide programs that encapsulate the kernel's suspend/resume functionality with the additional necessary tweaks. It also aims to provide a suspend-to-both functionality - this allows resuming from memory if battery is not depleted and resuming from disk if battery is completely depleted.
 
 
 
* [[TuxOnIce]] differs from pm-utils and uswsusp in that it attempts to directly patch the kernel's suspend/resume functionality to add more functionality than the default implementation. Therefore it requires a custom kernel.
 
 
 
* [[Suspending to RAM with hibernate-script]]
 
 
 
Note that the end goal of these packages is to provide binaries/scripts that can be invoked to perform suspend/resume. Actually hooking them up to power buttons or menu clicks or laptop lid events is left to other mechanisms. To automatically suspend/resume on certain power events, such as laptop lid close or battery depletion percentage, you may want to look into running [[Acpid]].
 
 
 
== Low level interfaces ==
 
 
 
Though these interfaces can be used directly, it is advisable to use some of [[#High level interfaces|high level interfaces]] to suspend/resume. Using low level interfaces directly is significantly faster using any high level interface, since running all the pre- and post-suspend hooks takes time, but hooks can properly set hardware clock, restore wireless etc.
 
 
 
=== kernel (swsusp) ===
 
 
 
The most straightforward approach is to directly inform the in-kernel software suspend code (swsusp) to enter a suspended state; the exact method and state depends on the level of hardware support. On modern kernels, writing appropriate strings to {{ic|/sys/power/state}} is the primary mechanism to trigger this suspend. See http://acpi.sourceforge.net/documentation/sleep.html for details.
 
 
 
For example, let us study out how pm-utils does this.
 
 
 
{{hc|/usr/lib/pm-utils/pm-functions  # from line 294, comments added|<nowiki>
 
if grep -q mem /sys/power/state; then
 
    SUSPEND_MODULE="kernel"
 
    # Suspend-to-RAM
 
    # ACPI State S3
 
    # Device State D3
 
    # Greatest power savings, slower resume
 
    do_suspend() { echo -n "mem" >/sys/power/state; }
 
elif [ -c /dev/pmu ] && pm-pmu --check; then
 
    SUSPEND_MODULE="kernel"
 
    # Suspend using Macintosh-style PMU
 
    # Fallback for older kernels in which the sysfs interface does not support this hardware
 
    do_suspend() { pm-pmu --suspend; }
 
elif grep -q standby /sys/power/state; then
 
    SUSPEND_MODULE="kernel"
 
    # Power-On-Suspend
 
    # ACPI State S1
 
    # Device State D1 (supported devices)
 
    # Minimal power savings, fast resume
 
    do_suspend() { echo -n "standby" >/sys/power/state; }
 
fi
 
</nowiki>}}
 
 
 
=== uswsusp ===
 
 
 
The uswsusp ('Userspace Software Suspend') provides ''s2ram'', a wrapper around the kernel's suspend-to-RAM mechanism, which performs some graphics adapter manipulations from userspace before suspending and after resuming.
 
 
 
See main article [[Uswsusp]].
 
 
 
=== tuxonice ===
 
 
 
TuxOnIce is a fork of the kernel implementation of suspend/resume that provides kernel patches to improve the default implementation. It requires a custom kernel to achieve this purpose.
 
 
 
See main article [[TuxOnIce]].
 
 
 
== High level interfaces ==
 
 
 
=== systemd ===
 
 
 
Systemd provides native commands for suspend, hibernate and a hybrid suspend, see [[Power Management#Power management with systemd]] for details.
 
 
 
See [[Power Management#Sleep hooks]] for additional information on configuring suspend/resume hooks. Also see {{ic|man systemctl}}, {{ic|man systemd-sleep}}, and {{ic|man systemd.special}}.
 
 
 
=== pm-utils ===
 
 
 
See main article [[pm-utils]].
 
 
 
== Troubleshooting ==
 
 
 
=== ACPI_OS_NAME ===
 
 
 
You might want to tweak your '''DSDT table''' to make it work. See [[DSDT]] article
 
 
 
== Other Resources ==
 
 
 
*[http://suspend.sourceforge.net/ Uswsusp Home Page]
 
*[http://en.wikipedia.org/wiki/Advanced_Configuration_and_Power_Interface Advanced Configuration and Power Interface]
 
*{{ic|/usr/share/doc/suspend/README}} Uswsusp Documentation
 
*{{ic|/usr/share/doc/suspend/README.s2ram-whitelist}} s2ram-whitelist README
 
*{{ic|/usr/src/linux-2.6.38-ARCH/Documentation/power/interface.txt}} Kernel Power Management Interface
 
*{{ic|/usr/src/linux-2.6.38-ARCH/Documentation/power/states.txt}} System Power Management States
 

Revision as of 20:49, 27 July 2013