-From kernel/suspend.c:
+Some warnings, first.
* BIG FAT WARNING *********************************************************
*
- * If you have unsupported (*) devices using DMA...
- * ...say goodbye to your data.
- *
* If you touch anything on disk between suspend and resume...
* ...kiss your data goodbye.
*
- * If your disk driver does not support suspend... (IDE does)
- * ...you'd better find out how to get along
- * without your data.
- *
- * If you change kernel command line between suspend and resume...
- * ...prepare for nasty fsck or worse.
+ * If you do resume from initrd after your filesystems are mounted...
+ * ...bye bye root partition.
+ * [this is actually same case as above]
*
- * If you change your hardware while system is suspended...
- * ...well, it was not good idea.
+ * 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 platform > /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).
Article about goals and implementation of Software Suspend for Linux
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-Author: G\82ábor Kuti
+Author: G\82ábor Kuti
Last revised: 2003-10-20 by Pavel Machek
Idea and goals to achieve
You have your server on UPS. Power died, and UPS is indicating 30
seconds to failure. What do you do? Suspend to disk.
-Ethernet card in your server died. You want to replace it. Your
-server is not hotplug capable. What do you do? Suspend to disk,
-replace ethernet card, resume. If you are fast your users will not
-even see broken connections.
-
Q: Maybe I'm missing something, but why don't the regular I/O paths work?
A: Yes. That's what echo platform > /sys/power/disk does.
-Q: My machine doesn't work with ACPI. How can I use swsusp than ?
-
-A: Do a reboot() syscall with right parameters. Warning: glibc gets in
-its way, so check with strace:
-
-reboot(LINUX_REBOOT_MAGIC1, LINUX_REBOOT_MAGIC2, 0xd000fce2)
-
-(Thanks to Peter Osterlund:)
-
-#include <unistd.h>
-#include <syscall.h>
-
-#define LINUX_REBOOT_MAGIC1 0xfee1dead
-#define LINUX_REBOOT_MAGIC2 672274793
-#define LINUX_REBOOT_CMD_SW_SUSPEND 0xD000FCE2
-
-int main()
-{
- syscall(SYS_reboot, LINUX_REBOOT_MAGIC1, LINUX_REBOOT_MAGIC2,
- LINUX_REBOOT_CMD_SW_SUSPEND, 0);
- return 0;
-}
-
-Also /sys/ interface should be still present.
-
Q: What is 'suspend2'?
A: suspend2 is 'Software Suspend 2', a forked implementation of
website, and not to the Linux Kernel Mailing List. We are working
toward merging suspend2 into the mainline kernel.
-Q: A kernel thread must voluntarily freeze itself (call 'refrigerator').
-I found some kernel threads that don't do it, and they don't freeze
-so the system can't sleep. Is this a known behavior?
+Q: What is the freezing of tasks and why are we using it?
-A: All such kernel threads need to be fixed, one by one. Select the
-place where the thread is safe to be frozen (no kernel semaphores
-should be held at that point and it must be safe to sleep there), and
-add:
+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.
- try_to_freeze(PF_FREEZE);
-
-If the thread is needed for writing the image to storage, you should
-instead set the PF_NOFREEZE process flag when creating the thread (and
-be very carefull).
-
-
-Q: What is the difference between between "platform", "shutdown" and
-"firmware" in /sys/power/disk?
+Q: What is the difference between "platform" and "shutdown"?
A:
platform: save state in linux, then tell bios to powerdown and blink
"suspended led"
-firmware: tell bios to save state itself [needs BIOS-specific suspend
- partition, and has very little to do with swsusp]
-
-"platform" is actually right thing to do, but "shutdown" is most
-reliable.
+"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 managment, that's okay. But
-its useless for suspend-to-disk. (And I do not see how you could use
+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
distinctions between SUSPEND and FREEZE.
A: Doing SUSPEND when you are asked to do FREEZE is always correct,
-but it may be unneccessarily slow. If you want USB to stay simple,
+but it may be unneccessarily 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 heavilly, leading to very bad interactivity.
+Q: After resuming, system is paging heavily, leading to very bad interactivity.
A: Try running
cat `cat /proc/[0-9]*/maps | grep / | sed 's:.* /:/:' | sort -u` > /dev/null
-after resume. swapoff -a; swapon -a may also be usefull.
+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?
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/disk/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: No. You can suspend successfully, but you'll not be able to
+resume. uswsusp should be able to work with LVM. See suspend.sf.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.
git://ftp.safe.ca / safe / jmp / linux-2.6 / blobdiff