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I have a desktop PC where hibernation is enabled, but it is never used (AFAIK it has never been used).

However, there is a 12GB hiberfil.sys file in the root directory of drive C: (SSD).

I was considering disabling hibernation (powercfg -h off from elevated cmd line) in order to delete this file to claim back this much needed drive space.

However, I've noticed that the last-modification timestamp of this file is updated everytime the system is "restarted" or even "cold booted" after a complete shutdown.

Is this file actively used outside of hibernation - during boot? Or, the fact that the last-modification of this file changes is just a by-product of hibernation being enabled in the first place?

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    I am not sure about when the file gets updated but If you don't use hibernation, simply turn it off and you won't see any erroneous behavior as a result. I do it on most (not all) of my machines.
    – Señor CMasMas
    Commented Feb 27, 2020 at 19:51
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    @SeñorCMasMas its definitely used by fast startup, because that puts the system to hibernation.
    – LPChip
    Commented Feb 27, 2020 at 20:09
  • It is used by fast startup, due to the fact, fast startup is a hybrid hibernation power mode. You might be able to adjust the size of the file. If your system fails to compress everything into the smaller file, take note of the BSOD you will receive, sadly if that does not work the only alternative is to disable it entirely.
    – Ramhound
    Commented Feb 27, 2020 at 21:32

2 Answers 2

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In Windows 8 and up, when you shutdown the computer with Fast Startup enabled, windows is not actually shutdown. Instead, all programs are closed, and then the system is placed in hibernation.

So yes, you are actually using Hibernation even if you are not realizing it. This is also why it makes a huge difference to turn off the pc, then turn on, or to reboot, when it comes to troubleshooting an issue.

By disabling hibernation, you basically turn off hybrid shutdown. Instead the system will shutdown normally, and as a result, the system will also boot much slower. If you really need the space, you can of course disable the feature.

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Windows 10 Fast Startup also uses hiberfil.sys, but if you turn off both Fast Startup and Hibernation, that file is automatically deleted.

For dual-boot systems, you probably want both those features turned off, or access to the Windows OS partition would be denied or read-only.

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    -1 because this is partially incorrect. Fast Startup depends on Hibernation. Disabling hibernation will automatically stop Fast Startup (aka Hybrid shutdown) and turn it into a regular shutdown.
    – LPChip
    Commented Feb 27, 2020 at 20:12

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