swsusp.rst

Swap suspend

Some warnings, first.

Warning

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.)

Swap partition:

You need to append resume=/dev/your_swap_partition to kernel command line or specify it using /sys/power/resume.

Swap file:

If using a swapfile you can also specify a resume offset using resume_offset=<number> on the kernel command line or specify it in /sys/power/resume_offset.

After preparing 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 around 2/5 of available RAM by default).