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d7ae79c7 | 1 | Some warnings, first. |
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2 | |
3 | * BIG FAT WARNING ********************************************************* | |
4 | * | |
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5 | * If you touch anything on disk between suspend and resume... |
6 | * ...kiss your data goodbye. | |
7 | * | |
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8 | * If you do resume from initrd after your filesystems are mounted... |
9 | * ...bye bye root partition. | |
10 | * [this is actually same case as above] | |
1da177e4 | 11 | * |
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12 | * If you have unsupported (*) devices using DMA, you may have some |
13 | * problems. If your disk driver does not support suspend... (IDE does), | |
14 | * it may cause some problems, too. If you change kernel command line | |
15 | * between suspend and resume, it may do something wrong. If you change | |
16 | * your hardware while system is suspended... well, it was not good idea; | |
17 | * but it will probably only crash. | |
1da177e4 LT |
18 | * |
19 | * (*) suspend/resume support is needed to make it safe. | |
543cc27d | 20 | * |
b9827e4b | 21 | * If you have any filesystems on USB devices mounted before software suspend, |
543cc27d | 22 | * they won't be accessible after resume and you may lose data, as though |
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23 | * you have unplugged the USB devices with mounted filesystems on them; |
24 | * see the FAQ below for details. (This is not true for more traditional | |
25 | * power states like "standby", which normally don't turn USB off.) | |
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26 | |
27 | You need to append resume=/dev/your_swap_partition to kernel command | |
28 | line. Then you suspend by | |
29 | ||
30 | echo shutdown > /sys/power/disk; echo disk > /sys/power/state | |
31 | ||
32 | . If you feel ACPI works pretty well on your system, you might try | |
33 | ||
34 | echo platform > /sys/power/disk; echo disk > /sys/power/state | |
35 | ||
62c552cc BS |
36 | . If you would like to write hibernation image to swap and then suspend |
37 | to RAM (provided your platform supports it), you can try | |
38 | ||
39 | echo suspend > /sys/power/disk; echo disk > /sys/power/state | |
40 | ||
543cc27d PM |
41 | . If you have SATA disks, you'll need recent kernels with SATA suspend |
42 | support. For suspend and resume to work, make sure your disk drivers | |
43 | are built into kernel -- not modules. [There's way to make | |
44 | suspend/resume with modular disk drivers, see FAQ, but you probably | |
45 | should not do that.] | |
46 | ||
853609b6 | 47 | If you want to limit the suspend image size to N bytes, do |
ca0aec0f RW |
48 | |
49 | echo N > /sys/power/image_size | |
50 | ||
51 | before suspend (it is limited to 500 MB by default). | |
1da177e4 | 52 | |
1c936699 SC |
53 | . The resume process checks for the presence of the resume device, |
54 | if found, it then checks the contents for the hibernation image signature. | |
55 | If both are found, it resumes the hibernation image. | |
56 | ||
57 | . The resume process may be triggered in two ways: | |
58 | 1) During lateinit: If resume=/dev/your_swap_partition is specified on | |
59 | the kernel command line, lateinit runs the resume process. If the | |
60 | resume device has not been probed yet, the resume process fails and | |
61 | bootup continues. | |
62 | 2) Manually from an initrd or initramfs: May be run from | |
63 | the init script by using the /sys/power/resume file. It is vital | |
64 | that this be done prior to remounting any filesystems (even as | |
65 | read-only) otherwise data may be corrupted. | |
1da177e4 LT |
66 | |
67 | Article about goals and implementation of Software Suspend for Linux | |
68 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
1557cc42 | 69 | Author: Gábor Kuti |
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70 | Last revised: 2003-10-20 by Pavel Machek |
71 | ||
72 | Idea and goals to achieve | |
73 | ||
74 | Nowadays it is common in several laptops that they have a suspend button. It | |
75 | saves the state of the machine to a filesystem or to a partition and switches | |
76 | to standby mode. Later resuming the machine the saved state is loaded back to | |
77 | ram and the machine can continue its work. It has two real benefits. First we | |
78 | save ourselves the time machine goes down and later boots up, energy costs | |
79 | are real high when running from batteries. The other gain is that we don't have to | |
80 | interrupt our programs so processes that are calculating something for a long | |
81 | time shouldn't need to be written interruptible. | |
82 | ||
83 | swsusp saves the state of the machine into active swaps and then reboots or | |
84 | powerdowns. You must explicitly specify the swap partition to resume from with | |
85 | ``resume='' kernel option. If signature is found it loads and restores saved | |
86 | state. If the option ``noresume'' is specified as a boot parameter, it skips | |
f996fc96 BS |
87 | the resuming. If the option ``hibernate=nocompress'' is specified as a boot |
88 | parameter, it saves hibernation image without compression. | |
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89 | |
90 | In the meantime while the system is suspended you should not add/remove any | |
91 | of the hardware, write to the filesystems, etc. | |
92 | ||
93 | Sleep states summary | |
94 | ==================== | |
95 | ||
96 | There are three different interfaces you can use, /proc/acpi should | |
97 | work like this: | |
98 | ||
99 | In a really perfect world: | |
100 | echo 1 > /proc/acpi/sleep # for standby | |
101 | echo 2 > /proc/acpi/sleep # for suspend to ram | |
102 | echo 3 > /proc/acpi/sleep # for suspend to ram, but with more power conservative | |
103 | echo 4 > /proc/acpi/sleep # for suspend to disk | |
104 | echo 5 > /proc/acpi/sleep # for shutdown unfriendly the system | |
105 | ||
106 | and perhaps | |
107 | echo 4b > /proc/acpi/sleep # for suspend to disk via s4bios | |
108 | ||
109 | Frequently Asked Questions | |
110 | ========================== | |
111 | ||
112 | Q: well, suspending a server is IMHO a really stupid thing, | |
113 | but... (Diego Zuccato): | |
114 | ||
115 | A: You bought new UPS for your server. How do you install it without | |
116 | bringing machine down? Suspend to disk, rearrange power cables, | |
117 | resume. | |
118 | ||
119 | You have your server on UPS. Power died, and UPS is indicating 30 | |
120 | seconds to failure. What do you do? Suspend to disk. | |
121 | ||
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122 | |
123 | Q: Maybe I'm missing something, but why don't the regular I/O paths work? | |
124 | ||
125 | A: We do use the regular I/O paths. However we cannot restore the data | |
126 | to its original location as we load it. That would create an | |
127 | inconsistent kernel state which would certainly result in an oops. | |
128 | Instead, we load the image into unused memory and then atomically copy | |
129 | it back to it original location. This implies, of course, a maximum | |
130 | image size of half the amount of memory. | |
131 | ||
132 | There are two solutions to this: | |
133 | ||
134 | * require half of memory to be free during suspend. That way you can | |
135 | read "new" data onto free spots, then cli and copy | |
136 | ||
137 | * assume we had special "polling" ide driver that only uses memory | |
138 | between 0-640KB. That way, I'd have to make sure that 0-640KB is free | |
139 | during suspending, but otherwise it would work... | |
140 | ||
141 | suspend2 shares this fundamental limitation, but does not include user | |
142 | data and disk caches into "used memory" by saving them in | |
143 | advance. That means that the limitation goes away in practice. | |
144 | ||
145 | Q: Does linux support ACPI S4? | |
146 | ||
147 | A: Yes. That's what echo platform > /sys/power/disk does. | |
148 | ||
1da177e4 LT |
149 | Q: What is 'suspend2'? |
150 | ||
151 | A: suspend2 is 'Software Suspend 2', a forked implementation of | |
152 | suspend-to-disk which is available as separate patches for 2.4 and 2.6 | |
153 | kernels from swsusp.sourceforge.net. It includes support for SMP, 4GB | |
154 | highmem and preemption. It also has a extensible architecture that | |
155 | allows for arbitrary transformations on the image (compression, | |
156 | encryption) and arbitrary backends for writing the image (eg to swap | |
157 | or an NFS share[Work In Progress]). Questions regarding suspend2 | |
158 | should be sent to the mailing list available through the suspend2 | |
159 | website, and not to the Linux Kernel Mailing List. We are working | |
160 | toward merging suspend2 into the mainline kernel. | |
161 | ||
83144186 | 162 | Q: What is the freezing of tasks and why are we using it? |
1da177e4 | 163 | |
83144186 RW |
164 | A: The freezing of tasks is a mechanism by which user space processes and some |
165 | kernel threads are controlled during hibernation or system-wide suspend (on some | |
166 | architectures). See freezing-of-tasks.txt for details. | |
1da177e4 | 167 | |
11d77d0c | 168 | Q: What is the difference between "platform" and "shutdown"? |
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169 | |
170 | A: | |
171 | ||
172 | shutdown: save state in linux, then tell bios to powerdown | |
173 | ||
174 | platform: save state in linux, then tell bios to powerdown and blink | |
175 | "suspended led" | |
176 | ||
11d77d0c JB |
177 | "platform" is actually right thing to do where supported, but |
178 | "shutdown" is most reliable (except on ACPI systems). | |
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179 | |
180 | Q: I do not understand why you have such strong objections to idea of | |
181 | selective suspend. | |
182 | ||
2fe0ae78 ML |
183 | A: Do selective suspend during runtime power management, that's okay. But |
184 | it's useless for suspend-to-disk. (And I do not see how you could use | |
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185 | it for suspend-to-ram, I hope you do not want that). |
186 | ||
187 | Lets see, so you suggest to | |
188 | ||
189 | * SUSPEND all but swap device and parents | |
190 | * Snapshot | |
191 | * Write image to disk | |
192 | * SUSPEND swap device and parents | |
193 | * Powerdown | |
194 | ||
195 | Oh no, that does not work, if swap device or its parents uses DMA, | |
196 | you've corrupted data. You'd have to do | |
197 | ||
198 | * SUSPEND all but swap device and parents | |
199 | * FREEZE swap device and parents | |
200 | * Snapshot | |
201 | * UNFREEZE swap device and parents | |
202 | * Write | |
203 | * SUSPEND swap device and parents | |
204 | ||
205 | Which means that you still need that FREEZE state, and you get more | |
206 | complicated code. (And I have not yet introduce details like system | |
207 | devices). | |
208 | ||
209 | Q: There don't seem to be any generally useful behavioral | |
210 | distinctions between SUSPEND and FREEZE. | |
211 | ||
212 | A: Doing SUSPEND when you are asked to do FREEZE is always correct, | |
25985edc | 213 | but it may be unnecessarily slow. If you want your driver to stay simple, |
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214 | slowness may not matter to you. It can always be fixed later. |
215 | ||
216 | For devices like disk it does matter, you do not want to spindown for | |
217 | FREEZE. | |
218 | ||
2fe0ae78 | 219 | Q: After resuming, system is paging heavily, leading to very bad interactivity. |
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220 | |
221 | A: Try running | |
222 | ||
223 | cat `cat /proc/[0-9]*/maps | grep / | sed 's:.* /:/:' | sort -u` > /dev/null | |
224 | ||
a58a414f | 225 | after resume. swapoff -a; swapon -a may also be useful. |
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226 | |
227 | Q: What happens to devices during swsusp? They seem to be resumed | |
228 | during system suspend? | |
229 | ||
230 | A: That's correct. We need to resume them if we want to write image to | |
231 | disk. Whole sequence goes like | |
232 | ||
233 | Suspend part | |
234 | ~~~~~~~~~~~~ | |
235 | running system, user asks for suspend-to-disk | |
236 | ||
237 | user processes are stopped | |
238 | ||
239 | suspend(PMSG_FREEZE): devices are frozen so that they don't interfere | |
240 | with state snapshot | |
241 | ||
242 | state snapshot: copy of whole used memory is taken with interrupts disabled | |
243 | ||
244 | resume(): devices are woken up so that we can write image to swap | |
245 | ||
246 | write image to swap | |
247 | ||
248 | suspend(PMSG_SUSPEND): suspend devices so that we can power off | |
249 | ||
250 | turn the power off | |
251 | ||
252 | Resume part | |
253 | ~~~~~~~~~~~ | |
254 | (is actually pretty similar) | |
255 | ||
256 | running system, user asks for suspend-to-disk | |
257 | ||
25985edc | 258 | user processes are stopped (in common case there are none, but with resume-from-initrd, no one knows) |
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259 | |
260 | read image from disk | |
261 | ||
262 | suspend(PMSG_FREEZE): devices are frozen so that they don't interfere | |
263 | with image restoration | |
264 | ||
265 | image restoration: rewrite memory with image | |
266 | ||
267 | resume(): devices are woken up so that system can continue | |
268 | ||
269 | thaw all user processes | |
270 | ||
271 | Q: What is this 'Encrypt suspend image' for? | |
272 | ||
273 | A: First of all: it is not a replacement for dm-crypt encrypted swap. | |
274 | It cannot protect your computer while it is suspended. Instead it does | |
275 | protect from leaking sensitive data after resume from suspend. | |
276 | ||
277 | Think of the following: you suspend while an application is running | |
278 | that keeps sensitive data in memory. The application itself prevents | |
279 | the data from being swapped out. Suspend, however, must write these | |
280 | data to swap to be able to resume later on. Without suspend encryption | |
281 | your sensitive data are then stored in plaintext on disk. This means | |
282 | that after resume your sensitive data are accessible to all | |
283 | applications having direct access to the swap device which was used | |
284 | for suspend. If you don't need swap after resume these data can remain | |
285 | on disk virtually forever. Thus it can happen that your system gets | |
286 | broken in weeks later and sensitive data which you thought were | |
287 | encrypted and protected are retrieved and stolen from the swap device. | |
288 | To prevent this situation you should use 'Encrypt suspend image'. | |
289 | ||
290 | During suspend a temporary key is created and this key is used to | |
291 | encrypt the data written to disk. When, during resume, the data was | |
292 | read back into memory the temporary key is destroyed which simply | |
293 | means that all data written to disk during suspend are then | |
294 | inaccessible so they can't be stolen later on. The only thing that | |
295 | you must then take care of is that you call 'mkswap' for the swap | |
296 | partition used for suspend as early as possible during regular | |
297 | boot. This asserts that any temporary key from an oopsed suspend or | |
298 | from a failed or aborted resume is erased from the swap device. | |
299 | ||
300 | As a rule of thumb use encrypted swap to protect your data while your | |
301 | system is shut down or suspended. Additionally use the encrypted | |
302 | suspend image to prevent sensitive data from being stolen after | |
303 | resume. | |
7e958883 | 304 | |
ecbd0da1 | 305 | Q: Can I suspend to a swap file? |
7e958883 | 306 | |
ecbd0da1 RW |
307 | A: Generally, yes, you can. However, it requires you to use the "resume=" and |
308 | "resume_offset=" kernel command line parameters, so the resume from a swap file | |
309 | cannot be initiated from an initrd or initramfs image. See | |
310 | swsusp-and-swap-files.txt for details. | |
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311 | |
312 | Q: Is there a maximum system RAM size that is supported by swsusp? | |
313 | ||
314 | A: It should work okay with highmem. | |
315 | ||
316 | Q: Does swsusp (to disk) use only one swap partition or can it use | |
317 | multiple swap partitions (aggregate them into one logical space)? | |
318 | ||
319 | A: Only one swap partition, sorry. | |
320 | ||
321 | Q: If my application(s) causes lots of memory & swap space to be used | |
322 | (over half of the total system RAM), is it correct that it is likely | |
323 | to be useless to try to suspend to disk while that app is running? | |
324 | ||
325 | A: No, it should work okay, as long as your app does not mlock() | |
326 | it. Just prepare big enough swap partition. | |
327 | ||
a58a414f | 328 | Q: What information is useful for debugging suspend-to-disk problems? |
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329 | |
330 | A: Well, last messages on the screen are always useful. If something | |
331 | is broken, it is usually some kernel driver, therefore trying with as | |
332 | little as possible modules loaded helps a lot. I also prefer people to | |
333 | suspend from console, preferably without X running. Booting with | |
334 | init=/bin/bash, then swapon and starting suspend sequence manually | |
335 | usually does the trick. Then it is good idea to try with latest | |
336 | vanilla kernel. | |
337 | ||
543cc27d PM |
338 | Q: How can distributions ship a swsusp-supporting kernel with modular |
339 | disk drivers (especially SATA)? | |
340 | ||
341 | A: Well, it can be done, load the drivers, then do echo into | |
1c936699 | 342 | /sys/power/resume file from initrd. Be sure not to mount |
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343 | anything, not even read-only mount, or you are going to lose your |
344 | data. | |
345 | ||
346 | Q: How do I make suspend more verbose? | |
347 | ||
348 | A: If you want to see any non-error kernel messages on the virtual | |
349 | terminal the kernel switches to during suspend, you have to set the | |
e084dbd3 PM |
350 | kernel console loglevel to at least 4 (KERN_WARNING), for example by |
351 | doing | |
352 | ||
353 | # save the old loglevel | |
354 | read LOGLEVEL DUMMY < /proc/sys/kernel/printk | |
355 | # set the loglevel so we see the progress bar. | |
356 | # if the level is higher than needed, we leave it alone. | |
357 | if [ $LOGLEVEL -lt 5 ]; then | |
358 | echo 5 > /proc/sys/kernel/printk | |
359 | fi | |
360 | ||
361 | IMG_SZ=0 | |
362 | read IMG_SZ < /sys/power/image_size | |
363 | echo -n disk > /sys/power/state | |
364 | RET=$? | |
365 | # | |
366 | # the logic here is: | |
367 | # if image_size > 0 (without kernel support, IMG_SZ will be zero), | |
368 | # then try again with image_size set to zero. | |
369 | if [ $RET -ne 0 -a $IMG_SZ -ne 0 ]; then # try again with minimal image size | |
370 | echo 0 > /sys/power/image_size | |
371 | echo -n disk > /sys/power/state | |
372 | RET=$? | |
373 | fi | |
374 | ||
375 | # restore previous loglevel | |
376 | echo $LOGLEVEL > /proc/sys/kernel/printk | |
377 | exit $RET | |
543cc27d PM |
378 | |
379 | Q: Is this true that if I have a mounted filesystem on a USB device and | |
380 | I suspend to disk, I can lose data unless the filesystem has been mounted | |
381 | with "sync"? | |
382 | ||
b9827e4b DB |
383 | A: That's right ... if you disconnect that device, you may lose data. |
384 | In fact, even with "-o sync" you can lose data if your programs have | |
385 | information in buffers they haven't written out to a disk you disconnect, | |
386 | or if you disconnect before the device finished saving data you wrote. | |
543cc27d | 387 | |
b9827e4b DB |
388 | Software suspend normally powers down USB controllers, which is equivalent |
389 | to disconnecting all USB devices attached to your system. | |
390 | ||
391 | Your system might well support low-power modes for its USB controllers | |
392 | while the system is asleep, maintaining the connection, using true sleep | |
393 | modes like "suspend-to-RAM" or "standby". (Don't write "disk" to the | |
394 | /sys/power/state file; write "standby" or "mem".) We've not seen any | |
395 | hardware that can use these modes through software suspend, although in | |
11d77d0c JB |
396 | theory some systems might support "platform" modes that won't break the |
397 | USB connections. | |
543cc27d PM |
398 | |
399 | Remember that it's always a bad idea to unplug a disk drive containing a | |
b9827e4b DB |
400 | mounted filesystem. That's true even when your system is asleep! The |
401 | safest thing is to unmount all filesystems on removable media (such USB, | |
402 | Firewire, CompactFlash, MMC, external SATA, or even IDE hotplug bays) | |
403 | before suspending; then remount them after resuming. | |
d7ae79c7 | 404 | |
0458d5b4 AS |
405 | There is a work-around for this problem. For more information, see |
406 | Documentation/usb/persist.txt. | |
407 | ||
23b168d4 PM |
408 | Q: Can I suspend-to-disk using a swap partition under LVM? |
409 | ||
410 | A: No. You can suspend successfully, but you'll not be able to | |
411 | resume. uswsusp should be able to work with LVM. See suspend.sf.net. | |
412 | ||
e084dbd3 PM |
413 | Q: I upgraded the kernel from 2.6.15 to 2.6.16. Both kernels were |
414 | compiled with the similar configuration files. Anyway I found that | |
415 | suspend to disk (and resume) is much slower on 2.6.16 compared to | |
416 | 2.6.15. Any idea for why that might happen or how can I speed it up? | |
417 | ||
418 | A: This is because the size of the suspend image is now greater than | |
419 | for 2.6.15 (by saving more data we can get more responsive system | |
420 | after resume). | |
421 | ||
422 | There's the /sys/power/image_size knob that controls the size of the | |
423 | image. If you set it to 0 (eg. by echo 0 > /sys/power/image_size as | |
424 | root), the 2.6.15 behavior should be restored. If it is still too | |
425 | slow, take a look at suspend.sf.net -- userland suspend is faster and | |
426 | supports LZF compression to speed it up further. |