A recent update to the Linux kernel introduces a feature that permits users to cancel the hibernation process of their devices. This patch, proposed by Collabora“s Muhammad Anjum, aims to enhance user control during hibernation, although it also sheds light on broader challenges associated with sleep states.
Hibernation can require a significant amount of time to complete; Anjum notes that on his machine, this process takes around 20 seconds. The modification proposed in the request for comments allows users to interrupt the hibernation by pressing the power button. However, Anjum points out that implementing this feature involves complexities that may not be immediately apparent.
The hibernation feature has not been enabled by default in distributions like Ubuntu due to its potential risks. There is a comprehensive guide available for debugging hibernation issues, which can lead to severe consequences, including data loss. For example, while some machines may hibernate and successfully resume, users might find their keyboard and mouse unresponsive upon waking, leaving them unable to save their work properly. This unpredictability is a reason many distributions opt to keep hibernation disabled.
For those who decide to enable hibernation, the ability to cancel the process could prove beneficial. Regular updates to system firmware are likely to improve hibernation reliability, but many users neglect this important maintenance step. Tools like fwupd can assist with firmware updates, yet they require UEFI boot mode and sufficient space on the EFI system partition, which can pose challenges for older machines that might benefit the most from these updates.
The hibernation process itself involves saving all data held in memory to an SSD or hard disk, along with a snapshot of the operating system”s state before powering down. This state, defined as the deepest of four sleep levels by Intel, is known as Suspend-to-Disk. As described in resources like the Arch wiki, the other sleep states include Suspend-to-Idle, Standby, and Suspend-to-RAM. The advantage of hibernation is that it consumes no power, allowing users to disconnect the battery in older laptops if necessary.
However, there are drawbacks to this feature. Unlike Windows, which uses a specific file to store the memory image, Linux relies on the swap space designated for virtual memory, whether that is a swap file or a dedicated swap partition. For hibernation to work, the swap volume must be at least as large as the physical RAM. This requirement can create complications, particularly for systems with high memory usage, which may necessitate more swap space than available RAM.
Despite these limitations, hibernation remains a valuable tool, particularly when implemented in hybrid sleep mode. This approach combines the benefits of both hibernation and sleep by saving a hibernation image on disk while suspending to RAM. If the device has sufficient battery life, it resumes from sleep quickly; if the battery depletes, it can wake from hibernation instead.
As kernel developers like Anjum focus on improving hibernation support, there is hope for increased reliability and usage of this feature in the future.
