439 lines
17 KiB
Plaintext
439 lines
17 KiB
Plaintext
Some warnings, first.
|
|
|
|
* BIG FAT WARNING *********************************************************
|
|
*
|
|
* If you touch anything on disk between suspend and resume...
|
|
* ...kiss your data goodbye.
|
|
*
|
|
* If you do resume from initrd after your filesystems are mounted...
|
|
* ...bye bye root partition.
|
|
* [this is actually same case as above]
|
|
*
|
|
* If you have unsupported (*) devices using DMA, you may have some
|
|
* problems. If your disk driver does not support suspend... (IDE does),
|
|
* it may cause some problems, too. If you change kernel command line
|
|
* between suspend and resume, it may do something wrong. If you change
|
|
* your hardware while system is suspended... well, it was not good idea;
|
|
* but it will probably only crash.
|
|
*
|
|
* (*) suspend/resume support is needed to make it safe.
|
|
*
|
|
* If you have any filesystems on USB devices mounted before software suspend,
|
|
* they won't be accessible after resume and you may lose data, as though
|
|
* you have unplugged the USB devices with mounted filesystems on them;
|
|
* see the FAQ below for details. (This is not true for more traditional
|
|
* power states like "standby", which normally don't turn USB off.)
|
|
|
|
You need to append resume=/dev/your_swap_partition to kernel command
|
|
line. Then you suspend by
|
|
|
|
echo shutdown > /sys/power/disk; echo disk > /sys/power/state
|
|
|
|
. If you feel ACPI works pretty well on your system, you might try
|
|
|
|
echo platform > /sys/power/disk; echo disk > /sys/power/state
|
|
|
|
. If you would like to write hibernation image to swap and then suspend
|
|
to RAM (provided your platform supports it), you can try
|
|
|
|
echo suspend > /sys/power/disk; echo disk > /sys/power/state
|
|
|
|
. If you have SATA disks, you'll need recent kernels with SATA suspend
|
|
support. For suspend and resume to work, make sure your disk drivers
|
|
are built into kernel -- not modules. [There's way to make
|
|
suspend/resume with modular disk drivers, see FAQ, but you probably
|
|
should not do that.]
|
|
|
|
If you want to limit the suspend image size to N bytes, do
|
|
|
|
echo N > /sys/power/image_size
|
|
|
|
before suspend (it is limited to 500 MB by default).
|
|
|
|
. The resume process checks for the presence of the resume device,
|
|
if found, it then checks the contents for the hibernation image signature.
|
|
If both are found, it resumes the hibernation image.
|
|
|
|
. The resume process may be triggered in two ways:
|
|
1) During lateinit: If resume=/dev/your_swap_partition is specified on
|
|
the kernel command line, lateinit runs the resume process. If the
|
|
resume device has not been probed yet, the resume process fails and
|
|
bootup continues.
|
|
2) Manually from an initrd or initramfs: May be run from
|
|
the init script by using the /sys/power/resume file. It is vital
|
|
that this be done prior to remounting any filesystems (even as
|
|
read-only) otherwise data may be corrupted.
|
|
|
|
Article about goals and implementation of Software Suspend for Linux
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
Author: Gábor Kuti
|
|
Last revised: 2003-10-20 by Pavel Machek
|
|
|
|
Idea and goals to achieve
|
|
|
|
Nowadays it is common in several laptops that they have a suspend button. It
|
|
saves the state of the machine to a filesystem or to a partition and switches
|
|
to standby mode. Later resuming the machine the saved state is loaded back to
|
|
ram and the machine can continue its work. It has two real benefits. First we
|
|
save ourselves the time machine goes down and later boots up, energy costs
|
|
are real high when running from batteries. The other gain is that we don't have to
|
|
interrupt our programs so processes that are calculating something for a long
|
|
time shouldn't need to be written interruptible.
|
|
|
|
swsusp saves the state of the machine into active swaps and then reboots or
|
|
powerdowns. You must explicitly specify the swap partition to resume from with
|
|
``resume='' kernel option. If signature is found it loads and restores saved
|
|
state. If the option ``noresume'' is specified as a boot parameter, it skips
|
|
the resuming. If the option ``hibernate=nocompress'' is specified as a boot
|
|
parameter, it saves hibernation image without compression.
|
|
|
|
In the meantime while the system is suspended you should not add/remove any
|
|
of the hardware, write to the filesystems, etc.
|
|
|
|
Sleep states summary
|
|
====================
|
|
|
|
There are three different interfaces you can use, /proc/acpi should
|
|
work like this:
|
|
|
|
In a really perfect world:
|
|
echo 1 > /proc/acpi/sleep # for standby
|
|
echo 2 > /proc/acpi/sleep # for suspend to ram
|
|
echo 3 > /proc/acpi/sleep # for suspend to ram, but with more power conservative
|
|
echo 4 > /proc/acpi/sleep # for suspend to disk
|
|
echo 5 > /proc/acpi/sleep # for shutdown unfriendly the system
|
|
|
|
and perhaps
|
|
echo 4b > /proc/acpi/sleep # for suspend to disk via s4bios
|
|
|
|
Frequently Asked Questions
|
|
==========================
|
|
|
|
Q: well, suspending a server is IMHO a really stupid thing,
|
|
but... (Diego Zuccato):
|
|
|
|
A: You bought new UPS for your server. How do you install it without
|
|
bringing machine down? Suspend to disk, rearrange power cables,
|
|
resume.
|
|
|
|
You have your server on UPS. Power died, and UPS is indicating 30
|
|
seconds to failure. What do you do? Suspend to disk.
|
|
|
|
|
|
Q: Maybe I'm missing something, but why don't the regular I/O paths work?
|
|
|
|
A: We do use the regular I/O paths. However we cannot restore the data
|
|
to its original location as we load it. That would create an
|
|
inconsistent kernel state which would certainly result in an oops.
|
|
Instead, we load the image into unused memory and then atomically copy
|
|
it back to it original location. This implies, of course, a maximum
|
|
image size of half the amount of memory.
|
|
|
|
There are two solutions to this:
|
|
|
|
* require half of memory to be free during suspend. That way you can
|
|
read "new" data onto free spots, then cli and copy
|
|
|
|
* assume we had special "polling" ide driver that only uses memory
|
|
between 0-640KB. That way, I'd have to make sure that 0-640KB is free
|
|
during suspending, but otherwise it would work...
|
|
|
|
suspend2 shares this fundamental limitation, but does not include user
|
|
data and disk caches into "used memory" by saving them in
|
|
advance. That means that the limitation goes away in practice.
|
|
|
|
Q: Does linux support ACPI S4?
|
|
|
|
A: Yes. That's what echo platform > /sys/power/disk does.
|
|
|
|
Q: What is 'suspend2'?
|
|
|
|
A: suspend2 is 'Software Suspend 2', a forked implementation of
|
|
suspend-to-disk which is available as separate patches for 2.4 and 2.6
|
|
kernels from swsusp.sourceforge.net. It includes support for SMP, 4GB
|
|
highmem and preemption. It also has a extensible architecture that
|
|
allows for arbitrary transformations on the image (compression,
|
|
encryption) and arbitrary backends for writing the image (eg to swap
|
|
or an NFS share[Work In Progress]). Questions regarding suspend2
|
|
should be sent to the mailing list available through the suspend2
|
|
website, and not to the Linux Kernel Mailing List. We are working
|
|
toward merging suspend2 into the mainline kernel.
|
|
|
|
Q: What is the freezing of tasks and why are we using it?
|
|
|
|
A: The freezing of tasks is a mechanism by which user space processes and some
|
|
kernel threads are controlled during hibernation or system-wide suspend (on some
|
|
architectures). See freezing-of-tasks.txt for details.
|
|
|
|
Q: What is the difference between "platform" and "shutdown"?
|
|
|
|
A:
|
|
|
|
shutdown: save state in linux, then tell bios to powerdown
|
|
|
|
platform: save state in linux, then tell bios to powerdown and blink
|
|
"suspended led"
|
|
|
|
"platform" is actually right thing to do where supported, but
|
|
"shutdown" is most reliable (except on ACPI systems).
|
|
|
|
Q: I do not understand why you have such strong objections to idea of
|
|
selective suspend.
|
|
|
|
A: Do selective suspend during runtime power management, that's okay. But
|
|
it's useless for suspend-to-disk. (And I do not see how you could use
|
|
it for suspend-to-ram, I hope you do not want that).
|
|
|
|
Lets see, so you suggest to
|
|
|
|
* SUSPEND all but swap device and parents
|
|
* Snapshot
|
|
* Write image to disk
|
|
* SUSPEND swap device and parents
|
|
* Powerdown
|
|
|
|
Oh no, that does not work, if swap device or its parents uses DMA,
|
|
you've corrupted data. You'd have to do
|
|
|
|
* SUSPEND all but swap device and parents
|
|
* FREEZE swap device and parents
|
|
* Snapshot
|
|
* UNFREEZE swap device and parents
|
|
* Write
|
|
* SUSPEND swap device and parents
|
|
|
|
Which means that you still need that FREEZE state, and you get more
|
|
complicated code. (And I have not yet introduce details like system
|
|
devices).
|
|
|
|
Q: There don't seem to be any generally useful behavioral
|
|
distinctions between SUSPEND and FREEZE.
|
|
|
|
A: Doing SUSPEND when you are asked to do FREEZE is always correct,
|
|
but it may be unnecessarily slow. If you want your driver to stay simple,
|
|
slowness may not matter to you. It can always be fixed later.
|
|
|
|
For devices like disk it does matter, you do not want to spindown for
|
|
FREEZE.
|
|
|
|
Q: After resuming, system is paging heavily, leading to very bad interactivity.
|
|
|
|
A: Try running
|
|
|
|
cat /proc/[0-9]*/maps | grep / | sed 's:.* /:/:' | sort -u | while read file
|
|
do
|
|
test -f "$file" && cat "$file" > /dev/null
|
|
done
|
|
|
|
after resume. swapoff -a; swapon -a may also be useful.
|
|
|
|
Q: What happens to devices during swsusp? They seem to be resumed
|
|
during system suspend?
|
|
|
|
A: That's correct. We need to resume them if we want to write image to
|
|
disk. Whole sequence goes like
|
|
|
|
Suspend part
|
|
~~~~~~~~~~~~
|
|
running system, user asks for suspend-to-disk
|
|
|
|
user processes are stopped
|
|
|
|
suspend(PMSG_FREEZE): devices are frozen so that they don't interfere
|
|
with state snapshot
|
|
|
|
state snapshot: copy of whole used memory is taken with interrupts disabled
|
|
|
|
resume(): devices are woken up so that we can write image to swap
|
|
|
|
write image to swap
|
|
|
|
suspend(PMSG_SUSPEND): suspend devices so that we can power off
|
|
|
|
turn the power off
|
|
|
|
Resume part
|
|
~~~~~~~~~~~
|
|
(is actually pretty similar)
|
|
|
|
running system, user asks for suspend-to-disk
|
|
|
|
user processes are stopped (in common case there are none, but with resume-from-initrd, no one knows)
|
|
|
|
read image from disk
|
|
|
|
suspend(PMSG_FREEZE): devices are frozen so that they don't interfere
|
|
with image restoration
|
|
|
|
image restoration: rewrite memory with image
|
|
|
|
resume(): devices are woken up so that system can continue
|
|
|
|
thaw all user processes
|
|
|
|
Q: What is this 'Encrypt suspend image' for?
|
|
|
|
A: First of all: it is not a replacement for dm-crypt encrypted swap.
|
|
It cannot protect your computer while it is suspended. Instead it does
|
|
protect from leaking sensitive data after resume from suspend.
|
|
|
|
Think of the following: you suspend while an application is running
|
|
that keeps sensitive data in memory. The application itself prevents
|
|
the data from being swapped out. Suspend, however, must write these
|
|
data to swap to be able to resume later on. Without suspend encryption
|
|
your sensitive data are then stored in plaintext on disk. This means
|
|
that after resume your sensitive data are accessible to all
|
|
applications having direct access to the swap device which was used
|
|
for suspend. If you don't need swap after resume these data can remain
|
|
on disk virtually forever. Thus it can happen that your system gets
|
|
broken in weeks later and sensitive data which you thought were
|
|
encrypted and protected are retrieved and stolen from the swap device.
|
|
To prevent this situation you should use 'Encrypt suspend image'.
|
|
|
|
During suspend a temporary key is created and this key is used to
|
|
encrypt the data written to disk. When, during resume, the data was
|
|
read back into memory the temporary key is destroyed which simply
|
|
means that all data written to disk during suspend are then
|
|
inaccessible so they can't be stolen later on. The only thing that
|
|
you must then take care of is that you call 'mkswap' for the swap
|
|
partition used for suspend as early as possible during regular
|
|
boot. This asserts that any temporary key from an oopsed suspend or
|
|
from a failed or aborted resume is erased from the swap device.
|
|
|
|
As a rule of thumb use encrypted swap to protect your data while your
|
|
system is shut down or suspended. Additionally use the encrypted
|
|
suspend image to prevent sensitive data from being stolen after
|
|
resume.
|
|
|
|
Q: Can I suspend to a swap file?
|
|
|
|
A: Generally, yes, you can. However, it requires you to use the "resume=" and
|
|
"resume_offset=" kernel command line parameters, so the resume from a swap file
|
|
cannot be initiated from an initrd or initramfs image. See
|
|
swsusp-and-swap-files.txt for details.
|
|
|
|
Q: Is there a maximum system RAM size that is supported by swsusp?
|
|
|
|
A: It should work okay with highmem.
|
|
|
|
Q: Does swsusp (to disk) use only one swap partition or can it use
|
|
multiple swap partitions (aggregate them into one logical space)?
|
|
|
|
A: Only one swap partition, sorry.
|
|
|
|
Q: If my application(s) causes lots of memory & swap space to be used
|
|
(over half of the total system RAM), is it correct that it is likely
|
|
to be useless to try to suspend to disk while that app is running?
|
|
|
|
A: No, it should work okay, as long as your app does not mlock()
|
|
it. Just prepare big enough swap partition.
|
|
|
|
Q: What information is useful for debugging suspend-to-disk problems?
|
|
|
|
A: Well, last messages on the screen are always useful. If something
|
|
is broken, it is usually some kernel driver, therefore trying with as
|
|
little as possible modules loaded helps a lot. I also prefer people to
|
|
suspend from console, preferably without X running. Booting with
|
|
init=/bin/bash, then swapon and starting suspend sequence manually
|
|
usually does the trick. Then it is good idea to try with latest
|
|
vanilla kernel.
|
|
|
|
Q: How can distributions ship a swsusp-supporting kernel with modular
|
|
disk drivers (especially SATA)?
|
|
|
|
A: Well, it can be done, load the drivers, then do echo into
|
|
/sys/power/resume file from initrd. Be sure not to mount
|
|
anything, not even read-only mount, or you are going to lose your
|
|
data.
|
|
|
|
Q: How do I make suspend more verbose?
|
|
|
|
A: If you want to see any non-error kernel messages on the virtual
|
|
terminal the kernel switches to during suspend, you have to set the
|
|
kernel console loglevel to at least 4 (KERN_WARNING), for example by
|
|
doing
|
|
|
|
# save the old loglevel
|
|
read LOGLEVEL DUMMY < /proc/sys/kernel/printk
|
|
# set the loglevel so we see the progress bar.
|
|
# if the level is higher than needed, we leave it alone.
|
|
if [ $LOGLEVEL -lt 5 ]; then
|
|
echo 5 > /proc/sys/kernel/printk
|
|
fi
|
|
|
|
IMG_SZ=0
|
|
read IMG_SZ < /sys/power/image_size
|
|
echo -n disk > /sys/power/state
|
|
RET=$?
|
|
#
|
|
# the logic here is:
|
|
# if image_size > 0 (without kernel support, IMG_SZ will be zero),
|
|
# then try again with image_size set to zero.
|
|
if [ $RET -ne 0 -a $IMG_SZ -ne 0 ]; then # try again with minimal image size
|
|
echo 0 > /sys/power/image_size
|
|
echo -n disk > /sys/power/state
|
|
RET=$?
|
|
fi
|
|
|
|
# restore previous loglevel
|
|
echo $LOGLEVEL > /proc/sys/kernel/printk
|
|
exit $RET
|
|
|
|
Q: Is this true that if I have a mounted filesystem on a USB device and
|
|
I suspend to disk, I can lose data unless the filesystem has been mounted
|
|
with "sync"?
|
|
|
|
A: That's right ... if you disconnect that device, you may lose data.
|
|
In fact, even with "-o sync" you can lose data if your programs have
|
|
information in buffers they haven't written out to a disk you disconnect,
|
|
or if you disconnect before the device finished saving data you wrote.
|
|
|
|
Software suspend normally powers down USB controllers, which is equivalent
|
|
to disconnecting all USB devices attached to your system.
|
|
|
|
Your system might well support low-power modes for its USB controllers
|
|
while the system is asleep, maintaining the connection, using true sleep
|
|
modes like "suspend-to-RAM" or "standby". (Don't write "disk" to the
|
|
/sys/power/state file; write "standby" or "mem".) We've not seen any
|
|
hardware that can use these modes through software suspend, although in
|
|
theory some systems might support "platform" modes that won't break the
|
|
USB connections.
|
|
|
|
Remember that it's always a bad idea to unplug a disk drive containing a
|
|
mounted filesystem. That's true even when your system is asleep! The
|
|
safest thing is to unmount all filesystems on removable media (such USB,
|
|
Firewire, CompactFlash, MMC, external SATA, or even IDE hotplug bays)
|
|
before suspending; then remount them after resuming.
|
|
|
|
There is a work-around for this problem. For more information, see
|
|
Documentation/usb/persist.txt.
|
|
|
|
Q: Can I suspend-to-disk using a swap partition under LVM?
|
|
|
|
A: Yes and No. You can suspend successfully, but the kernel will not be able
|
|
to resume on its own. You need an initramfs that can recognize the resume
|
|
situation, activate the logical volume containing the swap volume (but not
|
|
touch any filesystems!), and eventually call
|
|
|
|
echo -n "$major:$minor" > /sys/power/resume
|
|
|
|
where $major and $minor are the respective major and minor device numbers of
|
|
the swap volume.
|
|
|
|
uswsusp works with LVM, too. See http://suspend.sourceforge.net/
|
|
|
|
Q: I upgraded the kernel from 2.6.15 to 2.6.16. Both kernels were
|
|
compiled with the similar configuration files. Anyway I found that
|
|
suspend to disk (and resume) is much slower on 2.6.16 compared to
|
|
2.6.15. Any idea for why that might happen or how can I speed it up?
|
|
|
|
A: This is because the size of the suspend image is now greater than
|
|
for 2.6.15 (by saving more data we can get more responsive system
|
|
after resume).
|
|
|
|
There's the /sys/power/image_size knob that controls the size of the
|
|
image. If you set it to 0 (eg. by echo 0 > /sys/power/image_size as
|
|
root), the 2.6.15 behavior should be restored. If it is still too
|
|
slow, take a look at suspend.sf.net -- userland suspend is faster and
|
|
supports LZF compression to speed it up further.
|