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KMUTIL(8) KernelManagement utility for kext collections KMUTIL(8)

kmutil <subcommand>

kmutil <load|unload|showloaded>

kmutil <find|libraries|print-diagnostics>

kmutil <create|inspect|check|log|dumpstate>

kmutil <clear-staging|trigger-panic-medic>

kmutil -h

kmutil is a multipurpose tool for managing kernel extensions (kexts) and kext collections on disk. It takes a subcommand and a number of options, some of which are common to multiple commands.

kmutil interacts with the KernelManagement subsystem for loading, unloading, and diagnosing kexts. It can also be used for inspecting the contents of a kext collection, interacting with the kernel to query load information, finding kexts and kext dependencies on disk, creating new collections of kexts, and displaying other diagnostic information.

Starting in macOS 11, kernel extensions are found in 3 different artifacts on disk. Each artifact is loaded exactly once at boot, and a kext must be linked into one of the three artifacts before it can be used.

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The boot kext collection contains the kernel and all system kexts necessary for starting and bootstrapping the operating system. It is an immutable artifact in /System/Library/KernelCollections. On Apple Silicon Macs, this artifact is kept exclusively in the Preboot volume.
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The system kext collection, if used, contains all remaining system kexts required by the operating system, and is loaded after boot. It is prelinked against the boot kext collection, and is also an immutable artifact in /System/Library/KernelCollections. Note that on Apple Silicon Macs, there is no system kext collection.
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The auxiliary kext collection, if built, contains kexts placed in /Library/Extensions and any other third-party kexts installed on the system. It is dynamically built by kernelmanagerd(8) and prelinked against the boot kext collection and, if present, the system kext collection. On Apple Silicon Macs, the auxiliary kext collection is located in the Preboot volume. For more information on installing third-party kexts into the auxiliary kext collection, see INSTALLING.

As of macOS 11, a kext is only loadable once it has been built into the auxiliary kext collection by kernelmanagerd(8), and the system has rebooted. At boot, kernelmanagerd(8) will load this collection into the kernel, which allows all of the kexts in the collection to match and load. If kmutil load, kextload(8), or any invocation of a KextManager function attempts to load a kext that is not yet loadable, kernelmanagerd(8) will stage the kext into a protected location, validate it, and prompt the user to approve a rebuild of the auxiliary kext collection. If the validation and rebuild are successful, the kext will be available on the next boot.

Commands and their specific options are listed below. For other options common to most commands, see OPTIONS.

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create: Create a new kext collection according to the options provided. This command should only be used by developers investigating custom kernels or replacing the contents of the boot kext collection or system kext collection. As of macOS 13.0, a KDK is required to create a new boot or system kext collection. To load or unload kexts already in a collection see the load and unload subcommands.
Specify one or more of boot, sys, or aux to build one or more collections at a time.
If building an auxiliary collection, don’t look for or generate a system kext collection.
Specify none, all, or allkexts (default: none) to strip symbol information after a kext has been built into a collection.
When building the boot kext collection, specify the path to the kernel. If -V is specified, kmutil will append the variant extension.
Only consider the bundle identifiers and paths explicitly specified, along with their dependencies.
—compress
Compress results using the LZFSE algorithm.
—img4-encode
Encode the collection in an img4 payload.
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inspect: Inspect & display the contents of a kext collection according to the options provided.
—show-mach-header
Print the mach header(s) in the collection(s). Use with —verbose to also display contents of inner fileset entries.
—show-fileset-entries
Only print mach header information present in fileset subentries. This is useful for determining prelink addresses and other load information about a kext in a collection.
—show-kext-load-addresses
When displaying the default output, include the load addresses of the kexts inline.
—show-kext-uuids
Include the UUIDs of each kext in the output.
—show-kernel-uuid
Print the UUID (and version) of the kernel if present in the collection. This will output nothing if a kernel is not found in the specified collection(s).
—show-kernel-uuid-only
Print the UUID of the kernel if present in the collection, and suppress default kext information.
—show-prelink-info
Dump the raw __PRELINK_INFO segment of the collection(s).
—show-collection-metadata
Print the metadata of the collection(s), such as their prelink uuids, the uuids of collections they link against, and the build version that produced the collection.
—show-mach-boot-properties
Print derived Mach-O boot properties of the collection(s).
—json
Output the section layout as JSON.
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load: Load the extension(s) specified with -b or -p. If the extension is not already in the auxiliary kext collection, the collection will be dynamically rebuilt by kernelmanagerd(8) for use on the next reboot. For more information, see INSTALLING. For kexts already contained in the boot, system, or auxiliary kext collection, the load subcommand will start the kext if it has not already been started.

For most kexts, the load subcommand must run as the superuser (root). Kexts installed under /System/ with an OSBundleAllowUserLoad property set to true may be loaded via the load subcommand by non-root users.

macOS 10.6 introduced C functions for loading kexts, KextManagerLoadKextWithIdentifier() and KextManagerLoadKextWithURL(), which are described in Apple’s developer documentation. These functions continue to be supported as of macOS 11.

If this kext is already loaded, send the named personality to the catalog.
Don’t use the default repositories for kexts. If you use this option, you will have to explicitly specify all dependencies of the kext being loaded, or otherwise worked on using the —repository option.
—load-style
Control the load style of the request to load extension. Valid options:
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start-and-match: Start the kernel extension and also begin matching on any accompanying personalities. (default)
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start-only: Start any specified kernel extensions but do not begin matching against any personalities provided by those extensions (unless matching has already started for them).
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match-only: Do not explictly start any of the given kernel extensions but do begin matching on IOKit personalities provided by them. This is useful to allow extensions that were previous loaded with start-only to now begin matching.
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unload: Unload the extension(s) specified with -b or -p. The extension must have been previously linked into a kext collection and loaded by the KernelManagement system. A successfull call to the unload subcommand will invoke the kext’s stop function and end the kext’s IOKit lifecycle, however the kext remains in kernel memory as part of the kext collection from which it was loaded. The extension will not be removed from any collection, including the auxiliary kext collection, and will still be available for loading without requiring a reboot.

If another loaded kext has a dependency on the kext being unloaded, the unload will fail. You can determine whether a kext has dependents using the showloaded subcommand.

Terminate all instances of the IOService class, but do not unload its kext or unload its personalities.
Terminate services and remove personalities only; do not unload kexts.
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libraries: Search for library kexts in the boot kext collection and the system kext collection (if available) that define symbols needed for linking the specified kexts, printing their bundle identifiers and versions. Information on symbols not found are printed after the library kext information for each architecture.

A handy use of the libraries subcommand is to run it with just the —xml flag and pipe the output to pbcopy(1). If the exit status is zero (indicating no undefined or multiply-defined symbols), you can open your kext’s Info.plist file in a text editor and paste the library declarations over the OSBundleLibraries property.

You can specify other collections with the libraries subcommand to look for dependencies in other collections as well.

—all-symbols
List all symbols; found, not found, or found more than once.
—onedef-symbols
List all symbols found, with the library kext they were found in.
—multdef-symbols
List all symbols found more than once, with their library kexts.
—undef-symbols
List all symbols not found in any library.
—unsupported
Look in unsupported kexts for symbols.
Use library kext compatible versions rather than current versions.
—xml
Print XML fragment suitable for pasting.
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showloaded: Display the status/information of loaded kernel extensions on the system, according to the options provided. By default, the following is shown for each kext:
The load index of the kext (used to track linkage references). Gaps in the list indicate kexts that have been unloaded.
The number of references to this kext by others. If nonzero, the kext cannot be unloaded.
The address in kernel space where the kext has been loaded.
The number of bytes of kernel memory that the kext occupies. If this is zero, the kext is a built-in part of the kernel that has an entry as a kext for resolving dependencies among kexts.
The number of wired bytes of kernel memory that the kext occupies.
The architecture of the kext, displayed only if using the —arch-info option.
The CFBundleIdentifier of the kext.
The CFBundleVersion of the kext.
<Linked Against>
The index numbers of all other kexts that this kext has a reference to.

The following options are available for the showloaded command:

—show-mach-headers
Show the mach headers of the loaded extensions and/or kernel, if —show-kernel is specified.
—show <loaded|unloaded|all>
Restrict output to a specific load state.
—collection <boot|sys|aux|codeless>
Restrict the load information to a particular kind. Defaults to all non-codeless kexts if unspecified. To display information about codeless kexts and dexts that the kernel knows about, use —collection codeless —show all.
—sort
Sort the output by load address of each extension, instead of by index.
—list-only
Print the list of extensions only, omitting the header on the first line.
—arch-info
Include the architecture info in output.
—no-kernel-components
Do not show kernel components in output.
—show-kernel
Show load information about the kernel in the output. Use with —show-mach-headers to view the kernel mach header.
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dumpstate: Display diagnostic information about the state of kernelmanagerd(8).
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find: Locate and print paths of kexts (or kexts in collections) matching the filter criteria. For more information on filtering, see FILTERING OPTIONS. Searches are performed using the same kext management logic used elsewhere in kmutil, by which only kexts specified with the repository or bundle options are eligible; this is specifically not an exhaustive, recursive filesystem search.
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check: Check that load information and/or kext collections on the system are consistent.
—collection-linkage
Check to see that the collections on the system are properly linked together by inspecting the UUID metadata in the prelink info section of each collection on the system.
—load-info
Check to see that the load information in the kernel properly mirrors the collections on disk. This is the default action if no other options are specified.
—kernel-only
If checking load info, just check that the kernel matches, and no other kexts.
—collection <boot|sys|aux>:
Restrict consistency check to one (or more) of the specified collection types. If unspecified, check all by default.
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log: Display logging information about the kext management subsystem. This is a wrapper around the system log(1) command with a pre-defined predicate to show only logs from kernelmanagerd and kmutil.
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print-diagnostics: Perform all possible tests on one or more kexts, and indicate whether or not the kext can be successfully built into a collection. If there are issues found with the kext, diagnostic information is reported which can help to isolate and resolve the problem. Note that some tests require root. Note that custom collections, variants, and architectures can be specified with the GENERIC and COLLECTION kmutil options.
Print diagnostics for the bundle specified at this path (can be specified more than once).
Don’t resolve kext dependencies
Recursively diagnose all kext dependencies of each kext specified with -p. Ignored when -Z is present.
—plugins
Diagnose each kext found in the PlugIns directory of kexts specified with -p.
—do-staging
Perform kext staging to the SIP protected location. This test requires root privileges.
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clear-staging: Clear the staging directory managed by kernelmanagerd(8) and kmutil(8).
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migrate: System subcommand used during a software update.
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install: System subcommand used to update the Boot and System kext collections.

The following commands can only be run in Recovery Mode.

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trigger-panic-medic: Remove the auxiliary kext collection and remove all kext approvals on the next boot. This subcommand can only be used in Recovery Mode. This command can be used to recover the system from a kext that causes a kernel panic. After calling trigger-panic-medic, all previously installed kexts will prompt the user to re-approve them when they are loaded or installed.
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configure-boot: Configure a custom boot object policy. This command can be used to install a custom mach-o file from which the system will boot. In order to install custom boot objects, you must first enter Medium Security by using the Startup Disk utility in Recovery Mode. Setting a custom boot object will further lower the system security to Permissive Security, and you will be prompted to confirm this action.
The Mach-O that the booter will load and start. The file can be optionally compressed and wrapped in an img4.
Compress the custom boot object
Install the custom boot object for the specified volume
—raw
Treat custom boot object as a raw file to be installed. The object will be installed with custom Mach-O boot properties derived from –lowest-virtual-address and –entry-point
—lowest-virtual-address
Lowest virtual memory address of the raw boot object. (iBoot will map the raw boot object at this virtual address)
—entry-point
Virtual memory address of entry point into the raw boot object

The following options are global to most kmutil subcommands.

Specify the architecture to use for the extensions or collections specified. Defaults to the current running architecture.
Specify a variant, i.e., development, debug, or kasan, of extensions or collections to prefer instead of the release defaults.
Disable staging and validation of extensions when performing an action.
Enable verbose output.
Paths to directories containing extensions. If -R is specified, the volume root will be automatically prepended.
Specify the target volume to operate on. Defaults to /.

The following options can be used in certain kmutil commands for filtering its input or output.

Include the bundle specified at this path in the results. Return an error if not found.
Search for, and/or include this identifier in the results. Return an error if not found.
—optional-identifier
Search for, and/or include this identifier in the results, if possible.
—elide-identifier
Do not include this identifier in the results.
Specify a filter, in predicate syntax, which must match against properties of an extension to be included in the input or output. This argument can be overridden by other arguments for specifying and including extensions.
Specify a filter, in predicate syntax, which must match against properties of an extension to be included in the input or output. This argument can not be overridden by other arguments for specifying and including extensions.
–kdk
The KDK path to use for discovering kexts when creating a new boot or sys kext collection.
–build
Use with caution. This specifies the build version number to use when discovering kexts and building kext collections. If no build version is specified, the current system build version number is used.

For more information on predicate filter syntax, see the predicate programming guide available in the Apple developer documentation.

The following options can be used to specify paths and options for handling kext collections. If left unspecified, collection paths will default to the default paths for the system kext collections.

The path to the boot kext collection.
The path to the system kext collection.
The path to the auxiliary kext collection.
Recover gracefully, where applicable, if a collection is missing.

Inspect the contents of system kext collections:

$ kmutil inspect -v --show-mach-header -B /System/Library/KernelCollections/BootKernelExtensions.kc
$ kmutil inspect --show-fileset-entries --bundle-identifier com.apple.kernel

Load and unload kexts:

$ kmutil load -b com.apple.filesystems.apfs
$ kmutil load -p /Library/Extensions/foo.kext
$ kmutil unload -p /System/Library/Extensions/apfs.kext

Show load information about kexts:

$ kmutil showloaded --show-mach-headers --bundle-identifier com.example.foo
$ kmutil showloaded --show-kernel --collection boot
$ kmutil showloaded --show unloaded --filter "'CFBundleVersion' == '15.2.13'"

Find dependencies of kexts:

$ kmutil libraries -p /Library/Extensions/foo.kext --xml | pbcopy

Create custom kext collections:

$ kmutil -n boot -B myboot.kc -k mykernel --elide-identifier com.apple.filesystems.apfs
$ kmutil -n boot sys -B myboot.kc -S mysys.kc -V debug
$ kmutil -n boot -B myboot.kc -k mykernel
$ kmutil -n sys -B myboot.kc -S mysys.kc -F "'OSBundleRequired' == 'Safe Boot'" -s stripkexts
$ kmutil -n aux -r /Library/Extensions -L

kmutil exits with a zero status on success. On error, kmutil prints an error message and then exits with a non-zero status.

Well known exit codes:

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3 : kmutil failed because the kext is missing when trying to unload it.
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27 : kmutil failed because user approval is required.
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28 : kmutil failed because a reboot is required.

For frequent users, kmutil can generate a shell completion script by invoking:

$ kmutil --generate-completion-script <shell>

This option supports zsh(1), bash(1), and fish. If no shell is specified, then a completion script will be generated for the current running shell.

kernelmanagerd(8)

2022-08-01