update_dyld_shared_cac... BSD General Commands Manualupdate_dyld_shared_cac...
NAME
update_dyld_shared_cache -- Updates dyld's shared cache
SYNOPSIS
update_dyld_shared_cache [-root directory] [-arch arch] [-force] [-debug] [-sort_by_name]
[-universal_boot]
DESCRIPTION
update_dyld_shared_cache ensures that dyld's shared cache is up-to-date. (This command can also be
called as update_prebinding.) Normally, this command never needs to be manually run. Instead, it is
automatically run by launchd when dyld notices the shared cache is out of date. To prevent the cache
from being regeneated during an install or during development of OS dylibs, dyld will not trigger a
shared cache rebuild if the environment variable DYLD_NO_FIX_PREBINDING is set, or if the main exe-cutable executable
cutable is a setuid binary, or alternate dylibs are loaded via one of the DYLD_ environment variables.
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 depenents 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 allosw you to update the shared cache on a non-running version of the OS.
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.
-sort_by_name
By default update_dyld_shared_cache assignes a random start address to each mach-o image in
the cache. This option causes the start addresses to be choosen in path order, thus subse-quent subsequent
quent runs will produce the same address layout which can help reproduce some bugs.
-universal_boot
This option can only be used running on an machine with an Intel processor. It builds
caches that can be used when booting on an Intel or a PowerPC based machine.
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)
Darwin March 23, 2007 Darwin
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