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OpenCore Configuration

Scheme

These properties are particularly relevant for older macOS operating systems. Refer to the Legacy Apple OS section for details on how to install and troubleshoot such macOS installations.

  1. CustomKernel
    • Type: plist boolean
    • Failsafe: false
    • Description: Use customised kernel cache from the Kernels directory located at the root of the ESP partition.

    Unsupported platforms including Atom and AMD require modified versions of XNU kernel in order to boot. This option provides the possibility to using a customised kernel cache which contains such modifications from ESP partition.

  2. FuzzyMatch
    • Type: plist boolean
    • Failsafe: false
    • Description: Use kernelcache with different checksums when available.

    On macOS 10.6 and earlier, kernelcache filename has a checksum, which essentially is adler32 from SMBIOS product name and EfiBoot device path. On certain firmware, the EfiBoot device path differs between UEFI and macOS due to ACPI or hardware specifics, rendering kernelcache checksum as always different.

    This setting allows matching the latest kernelcache with a suitable architecture when the kernelcache without suffix is unavailable, improving macOS 10.6 boot performance on several platforms.

  3. KernelArch
    • Type: plist string
    • Failsafe: Auto (Choose the preferred architecture automatically)
    • Description: Prefer specified kernel architecture (i386, i386-user32, x86_64) when available.

    On macOS 10.7 and earlier, the XNU kernel can boot with architectures different from the usual x86_64. This setting will use the specified architecture to boot macOS when it is supported by the macOS and the configuration:

    • i386 — Use i386 (32-bit) kernel when available.
    • i386-user32 — Use i386 (32-bit) kernel when available and force the use of 32-bit userspace on 64-bit capable processors if supported by the operating system. – On macOS, 64-bit capable processors are assumed to support SSSE3. This is not the case for older 64-bit capable Pentium processors, which cause some applications to crash on macOS 10.6. This behaviour corresponds to the -legacy kernel boot argument. – This option is unavailable on macOS 10.4 and 10.5 when running on 64-bit firmware due to an uninitialised 64-bit segment in the XNU kernel, which causes AppleEFIRuntime to incorrectly execute 64-bit code as 16-bit code.
    • x86_64 — Use x86_64 (64-bit) kernel when available.

    The algorithm used to determine the preferred kernel architecture is set out below.

    1. arch argument in image arguments (e.g. when launched via UEFI Shell) or in boot-args variable overrides any compatibility checks and forces the specified architecture, completing this algorithm.
    2. OpenCore build architecture restricts capabilities to i386 and i386-user32 mode for the 32-bit firmware variant.
    3. Determined EfiBoot version restricts architecture choice:
    • 10.4-10.5 — i386 or i386-user32 (only on 32-bit firmware)
    • 10.6 — i386, i386-user32, or x86_64
    • 10.7 — i386 or x86_64
    • 10.8 or newer — x86_64
    1. If KernelArch is set to Auto and SSSE3 is not supported by the CPU, capabilities are restricted to i386-user32 if supported by EfiBoot.
    2. Board identifier (from SMBIOS) based on EfiBoot version disables x86_64 support on an unsupported model if any i386 variant is supported. Auto is not consulted here as the list is not overridable in EfiBoot.
    3. KernelArch restricts the support to the explicitly specified architecture (when not set to Auto) if the architecture remains present in the capabilities.
    4. The best supported architecture is chosen in this order: x86_64, i386, i386-user32.

    Unlike macOS 10.7 (where certain board identifiers are treated as the i386 only machines), and macOS 10.5 or earlier (where x86_64 is not supported by the macOS kernel), macOS 10.6 is very special. The architecture choice on macOS 10.6 depends on many factors including not only the board identifier, but also the macOS product type (client vs server), macOS point release, and amount of RAM. The detection of all these is complicated and impractical, as several point releases had implementation flaws resulting in a failure to properly execute the server detection in the first place. For this reason, OpenCore on macOS 10.6 falls back on the x86_64 architecture whenever it is supported by the board, as it is on macOS 10.7.

    A 64-bit Mac model compatibility matrix corresponding to actual EfiBoot behaviour on macOS 10.6.8 and 10.7.5 is outlined below.

    Model 10.6 (Minimal) 10.6 (Client) 10.6 (Server) 10.7 (Any)
    Macmini 4,x (Mid 2010) 5,x (Mid 2011) 4,x (Mid 2010) 3,x (Early 2009)
    MacBook Unsupported Unsupported Unsupported 5,x (2009/09)
    MacBookAir Unsupported Unsupported Unsupported 2,x (Late 2008)
    MacBookPro 4,x (Early 2008) 8,x (Early 2011) 8,x (Early 2011) 3,x (Mid 2007)
    iMac 8,x (Early 2008) 12,x (Mid 2011) 12,x (Mid 2011) 7,x (Mid 2007)
    MacPro 3,x (Early 2008) 5,x (Mid 2010) 3,x (Early 2008) 3,x (Early 2008)
    Xserve 2,x (Early 2008) 2,x (Early 2008) 2,x (Early 2008) 2,x (Early 2008)

    Note: 3+2 and 6+4 hotkeys to choose the preferred architecture are unsupported as they are handled by EfiBoot and hence, difficult to detect.

  4. KernelCache
    • Type: plist string
    • Failsafe: Auto
    • Description: Prefer specified kernel cache type (Auto, Cacheless, Mkext, Prelinked) when available.

    Different variants of macOS support different kernel caching variants designed to improve boot performance. This setting prevents the use of faster kernel caching variants if slower variants are available for debugging and stability reasons. That is, by specifying Mkext, Prelinked will be disabled for e.g. 10.6 but not for 10.7. The list of available kernel caching types and its current support in OpenCore is listed below.

    macOS i386 NC i386 MK i386 PK x86_64 NC x86_64 MK x86_64 PK x86_64 KC
    10.4 YES YES (V1) NO (V1) - - - -
    10.5 YES YES (V1) NO (V1) - - - -
    10.6 YES YES (V2) YES(V2) YES YES(V2) YES(V2) -
    10.7 YES - YES(V3) YES - YES(V3) -
    10.8-10.9 - - - YES - YES(V3) -
    10.10-10.15 - - - - - YES(V3) -
    11+ - - - - - YES(V3) YES

    Note: The first version (V1) of the 32-bit prelinkedkernel is unsupported due to the corruption of kext symbol tables by the tools. On this version, the Auto setting will block prelinkedkernel booting. This also results in the keepsyms=1 boot argument being non-functional for kext frames on these systems.