Thread commands contain machine-specific data structures suitable for use in the thread state primitives. The machine specific data structures follow the struct thread_command as follows. Each flavor of machine specific data structure is preceded by an uint32_t constant for the flavor of that data structure, an uint32_t that is the count of uint32_t's of the size of the state data structure and then the state data structure follows. This triple may be repeated for many flavors. The constants for the flavors, counts and state data structure definitions are expected to be in the header file <machine/thread_status.h>. These machine specific data structures sizes must be multiples of 4 bytes. The cmdsize reflects the total size of the thread_command and all of the sizes of the constants for the flavors, counts and state data structures.

For executable objects that are unix processes there will be one thread_command (cmd == LC_UNIXTHREAD) created for it by the link-editor. This is the same as a LC_THREAD, except that a stack is automatically created (based on the shell's limit for the stack size). Command arguments and environment variables are copied onto that stack.