update_dyld_shared_cache(1)

NAME
update_dyld_shared_cache - Updates dyld's shared cache

SYNOPSIS
update_dyld_shared_cache [-root directory] [-overlay directory] [-arch arch] [-force] [-debug] [-universal_boot] [-verify]

DESCRIPTION
update_dyld_shared_cache ensures that dyld's shared cache is up-to-date. This tool is normally only run by Apple's Installer and Software Update, as they are the only official ways for OS dylibs to be updated. But if for some reason you used another mechanism to alter an OS dylib, you should manually run update_dyld_shared_cache.

Note that the new cache does not take effect until the OS is rebooted.

If a safe-boot is done (booting with shift key held down) the cache is deleted.

The dyld shared cache is mapped by dyld into a process at launch time. Later, when loading any mach-o image, dyld will first check if is in the share cache, and if it is will use that pre-bound version instead of opening, mapping, and binding the original file. This results in significant performance improvements to launch time.

update_dyld_shared_cache scans the directory /var/db/dyld/shared_region_roots for text files containing paths to mach-o executables. The full dependencies of all dylibs required by those executables is used to determine which libraries are commonly used and should be placed in the shared cache. If one of the text files contains a path to a dylib, that dylib and its dependents will be forced into the cache.

update_dyld_shared_cache builds a separate cache file for each architecture. The cache files and a readable text map of the cached are generated to /var/db/dyld.

You must be root to run this tool.

The options are as follows:

-root directory
    This option specifies the root of an OS installation for which dyld's shared cache should be updated. This is used by the Installer to update the dyld shared cache in a partition other than the one you into which you are currently booted. The cache files are created in the var/db/dyld directory of the specified directory. Note: if you are manually doing this, be sure to run the update_dyld_shared_cache tool that is in the partition being updated. This assures the cache format created will match that expected when booting off that partition.

-overlay directory
    This option specifies the root of a sparse directory tree. When building the dyld shared cache, any corresponding mach-o files in the sparse directory will override those in the boot partition. This is used by Software Update to build a dyld shared cache for the update that is about to be installed. The cache files are created in the var/db/dyld directory of the specified directory.

-arch arch
    By default update_dyld_shared_cache generates cache files for all architecture that the current machine can execute. You can override this behavior by specifying one or more -arch options and list exactly which architectures should have their shared caches updated.

-force
    This option will cause update_dyld_shared_cache to regenerated the shared cache files even if they appear to be already up-to-date.

-debug
    This option prints out additional information about the work being done.

-universal_boot
    This option builds caches for all machines.

-verify
    Will regenerate a shared cache in-memory that matches the randomization of the existing shared cache file. Then instead of writing the cache file, it compares the in-memory cache file to the on disk version and reports any differences.

FILES
/var/db/dyld/shared_region_roots directory of text files with paths to mach-o images used to determine what should be in shared cache.

SEE ALSO
dyld(1)