Power management/Suspend and hibernate
Currently there are available three methods of suspending: suspend to RAM (usually called just suspend), suspend to disk (usually known as hibernate), and hybrid suspend (sometimes aptly called suspend to both):
- Suspend to RAM method cuts power to most parts of the machine aside from the RAM, which is required to restore the machine's state. Because of the large power savings, it is advisable for laptops to automatically enter this mode when the computer is running on batteries and the lid is closed (or the user is inactive for some time).
- Suspend to disk method saves the machine's state into swap space and completely powers off the machine. When the machine is powered on, the state is restored. Until then, there is zero power consumption.
- Suspend to both method saves the machine's state into swap space, but does not power off the machine. Instead, it invokes usual suspend to RAM. Therefore, if the battery is not depleted, the system can resume from RAM. If the battery is depleted, the system can be resumed from disk, which is much slower than resuming from RAM, but the machine's state has not been lost.
There are multiple low level interfaces (backends) providing basic functionality, and some high level interfaces providing tweaks to handle problematic hardware drivers/kernel modules (e.g. video card re-initialization).
- 1 Low level interfaces
- 2 High level interfaces
- 3 Suspend to RAM
- 4 Hibernation
- 5 Troubleshooting
Low level interfaces
Though these interfaces can be used directly, it is advisable to use some of high level interfaces to suspend/hibernate. Using low level interfaces directly is significantly faster using any high level interface, since running all the pre- and post-suspend hooks takes time, but hooks can properly set hardware clock, restore wireless etc.
The most straightforward approach is to directly inform the in-kernel software suspend code (swsusp) to enter a suspended state; the exact method and state depends on the level of hardware support. On modern kernels, writing appropriate strings to
/sys/power/state is the primary mechanism to trigger this suspend.
See kernel documentation for details.
The uswsusp ('Userspace Software Suspend') is a wrapper around the kernel's suspend-to-RAM mechanism, which performs some graphics adapter manipulations from userspace before suspending and after resuming.
See main article Uswsusp.
TuxOnIce is a fork of the kernel implementation of suspend/hibernate that provides kernel patches to improve the default implementation. It requires a custom kernel to achieve this purpose.
See main article TuxOnIce.
High level interfaces
See Power Management#Sleep hooks for additional information on configuring suspend/hibernate hooks. Also see
man systemd-sleep, and
pm-utils is a set of shell scripts that encapsulate the backend's suspend/hibernate functionality. It comes with a set of pre- and post-suspend tweaks and various hooks to customize the process.
See main article pm-utils.
Suspend to RAM
Suspend to RAM should work out of the box.
In order to use hibernation, you need to create swap partition or swap file. See Swap for details.
About swap partition/file size
Even if your swap partition is smaller than RAM, you still have a big chance of hibernating successfully. According to kernel documentation:
/sys/power/image_sizecontrols the size of the image created by the suspend-to-disk mechanism. It can be written a string representing a non-negative integer that will be used as an upper limit of the image size, in bytes. The suspend-to-disk mechanism will do its best to ensure the image size will not exceed that number. However, if this turns out to be impossible, it will try to suspend anyway using the smallest image possible. In particular, if "0" is written to this file, the suspend image will be as small as possible. Reading from this file will display the current image size limit, which is set to 2/5 of available RAM by default.
You may either decrease the value of
/sys/power/image_size to make the suspend image as small as possible (for small swap partitions), or increase it to possibly speed up the hibernation process.
Required kernel parameters
The kernel parameter
resume=<swap_partition> has to be used. As
<swap_partition> you can use either kernel name of the swap partition, i.e.
/dev/sda1, or the UUID of the swap partition. See Kernel parameters for more examples for various bootloaders.
For example, with GRUB2 you can use
And if you use UUID instead:
Don't forget to run
grub-mkconfig -o /boot/grub/grub.cfg afterwards.
Hibernation into swap file
Using a swap file instead of a swap partition requires an additional kernel parameter
resume_offset=<Swap File Offset>.
The value of
<Swap File Offset> can be obtained by running
filefrag -v <Swap File>, the output is in a table format and the required value is located in the first row of the
physical_offset column. For example:
# filefrag -v /swapfile
Filesystem type is: ef53 File size of /swapfile is 4294967296 (1048576 blocks of 4096 bytes) ext: logical_offset: physical_offset: length: expected: flags: 0: 0.. 0: 38912.. 38912: 1: 1: 1.. 22527: 38913.. 61439: 22527: unwritten 2: 22528.. 53247: 899072.. 929791: 30720: 61440: unwritten ...
In the example the value of
<Swap File Offset> is
Recreate initial ramdisk
If you use an initramfs (default Arch systems do), you must add the
resume hook into the HOOKS in the configuration of mkinitcpio:
# resume must be placed after block and lvm2, but before filesystems HOOKS="... block lvm2 resume filesystems ..."
Finally, you must rebuild the initrd image for these changes to take effect:
# mkinitcpio -p linux
You might want to tweak your DSDT table to make it work. See DSDT article
Add acpi_sleep=nonvs kernel flag to your loader, and you are done!