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An open source kernel extension providing a sync between RTC variables and NVRAM. By design the mach kernel encrypts hibernate sleepimage and writes the encryption key to variable "IOHibernateRTCVariables" in the system registry (PMRootDomain). Somehow this value has to be written into RTC (or SMC) in order the boot.efi could read it. But in case if you have to limit your RTC memory to 1 bank (128 bytes), it doesn't work: there are no any variables in SMC/NVRAM/RTC (actually FakeSMC).

Fortunately, boot.efi can read key "IOHibernateRTCVariables" from NVRAM! This kext detects entering into "hibernate" power state, reads variable IOHibernateRTCVariables from the system registry and writes it to NVRAM.


  • Enables 'native' hibernation on PC's with hardware NVRAM on 10.10.5 and later. 'Native' means hibernation with encryption (standard hibernate modes 3 & 25)
  • Enables dumping NVRAM to file /nvram.plist before hibernation or panic


  • -hbfx-dump-nvram saves NVRAM to a file nvram.plist before hibernation and after kernel panic (with panic info)

  • -hbfx-disable-patch-pci disables patching of IOPCIFamily (this patch helps to avoid hang & black screen after resume (restoreMachineState won't be called for all devices)

  • hbfx-patch-pci=XHC,IMEI,IGPU allows to specify explicit device list (and restoreMachineState won't be called only for these devices). Also supports values none, false, off.

  • -hbfxdbg turns on debugging output

  • -hbfxbeta enables loading on unsupported osx

  • -hbfxoff disables kext loading

  • hbfx-ahbm=abhm_value controls auto-hibernation feature, where abhm_value is an arithmetic sum of respective values below:

    • EnableAutoHibernation = 1: If this flag is set, system will hibernate instead of regular sleep (flags below can be used to limit this behavior)
    • WhenLidIsClosed = 2: Auto hibernation can happen when lid is closed (if bit is not set - no matter which status lid has)
    • WhenExternalPowerIsDisconnected = 4: Auto hibernation can happen when external power is disconnected (if bit is not set - no matter whether it is connected)
    • WhenBatteryIsNotCharging = 8: Auto hibernation can happen when battery is not charging (if bit is not set - no matter whether it is charging)
    • WhenBatteryIsAtWarnLevel = 16: Auto hibernation can happen when battery is at warning level (macOS and battery kext are responsible for this level)
    • WhenBatteryAtCriticalLevel = 32: Auto hibernation can happen when battery is at critical level (macOS and battery kext are responsible for this level)
    • DoNotOverrideWakeUpTime = 64: Do not alter next wake up time, macOS is fully responsible for sleep maintenance dark wakes
    • DisableStimulusDarkWakeActivityTickle = 128: Disable power event kStimulusDarkWakeActivityTickle in kernel, so this event cannot trigger a switching from dark wake to full wake

    When when IOPMPowerSource cannot detect warning or critical battery level (it happens on hackintosh), next 4 bits can be used to specify minimal capacity percent remaining value when hibernation will be forced:

    • RemainCapacityBit1 = 256 (1)
    • RemainCapacityBit2 = 512 (2)
    • RemainCapacityBit3 = 1024 (4)
    • RemainCapacityBit4 = 2048 (8)

    Specified minimal capacity will be also used to put macOS into sleep/hibernate state (when the remaining capacity is less than it). 4 bits can be used to specify the battery levels from 1 to 15. Bits RemainCapacityBit1-RemainCapacityBit4 are 1,2,4,8 in percentage, so for example if you want to have 10 percent level to be the point where the laptop goes into sleep/hibernation, you would add Bits RemainCapacityBit4 and RemainCapacityBit2 which would be 2048+512=2560 (8+2=10 percent) in hbfx-ahbm. Bit EnableAutoHibernation defines a final state (sleep or hibernate).

NVRAM options

The following options can be stored in NVRAM (GUID = E09B9297-7928-4440-9AAB-D1F8536FBF0A), they can be used instead of respective boot-args

  • hbfx-dump-nvram - type Boolean
  • hbfx-disable-patch-pci - type Boolean
  • hbfx-patch-pci=XHC,IMEI,IGPU,none,false,off - type String
  • hbfx-ahbm - type Number