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Revision as of 09:34, 18 May 2006 by Zobel (Talk | contribs) (Kernel configuration)
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Software Suspend - swsusp

Software Suspend (swsusp) is a suspend-to-disk implementation included in the 2.6 kernel series. See Software Suspend 2 for an alternative implementation, which has some advantages.

Kernel configuration

To enable software suspend change your kernel config as follows:

Power management options → <*>Power management support (CONFIG_PM)
Power management options → <*>Software Suspend (CONFIG_SOFTWARE_SUSPEND)
Power management options → [/dev/resume_partition]Default resume partition (CONFIG_PM_STD_PARTITION)

/dev/resume_partition needs to be replaced by the swap partition you want to use for suspending. (Use # fdisk -l /dev/hda if unsure.)

You can override the default resume partition anytime by giving resume=/dev/resume_partition as kernel boot parameter. Also, in case you suspended, but want to boot up normally (without resuming from the saved image - losing all data that was unsaved at suspend time), you can give the noresume kernel boot parameter.

For some people suspending did not work if resume_partition was specified in the kernel config. In such case specify the resume partition as a kernel parameter instead.
When using Debian Etch or Sid, you need to use initramfs-tools as yaird is currently (2006-05-18) not supporting swsusp. See the Debian Wiki for more details.


To suspend you can either do a simple # echo disk > /sys/power/state (recommended) or use the patched SysVInit and call # swsusp or # shutdown -z now. As the /proc/acpi/sleep interface becomes deprecated in newer kernels you should NOT use the old # echo -n 4 > /proc/acpi/sleep anymore.

Ideally, you would do this from a script like /etc/acpi/actions/hibernate.sh. It has proven to be a good idea to shutdown the following processes/drivers within the script before you do the actual suspend:

  • any running mysql server
  • the linuxant driver may require to be stopped as well (# dldrstop does the trick).

Afterwards you might want to enable them again, as well as run a script that does necessary configurations according to the ac power state. Furthermore, the system clock is not readjusted automatically, so you will probably also want the do that from that script (i.e. by restarting your systemclock bootup script).

If the sound output is silent after resume, the following commands might help to get sound to work again without reloading any modules:

amixer set Master mute >/dev/null 2>&1
amixer set PCM mute >/dev/null 2>&1
amixer set Master unmute >/dev/null 2>&1
amixer set PCM unmute >/dev/null 2>&1

S5 vs. S4 state

Finally you should take note that swsusp does not set the ACPI S4 state. Instead it goes to S5. This means that the machine itself doesn't know that it was suspend rather than shutdown. Hence you can i.e. boot a parallel installed other operating system and resume your linux session later, as long as you don't touch the swap partition the image was saved to.