DYLD(1) General Commands Manual DYLD(1)
NAME
dyld - the dynamic link editor
SYNOPSIS
DYLD_FRAMEWORK_PATH
DYLD_FALLBACK_FRAMEWORK_PATH
DYLD_LIBRARY_PATH
DYLD_FALLBACK_LIBRARY_PATH
DYLD_INSERT_LIBRARIES
DYLD_FORCE_FLAT_NAMESPACE
DYLD_IMAGE_SUFFIX
DYLD_PRINT_LIBRARIES
DYLD_PRINT_LIBRARIES_POST_LAUNCH
DYLD_EBADEXEC_ONLY
DYLD_BIND_AT_LAUNCH
DYLD_DEAD_LOCK_HANG
DYLD_PREBIND_DEBUG
DYLD_ABORT_MULTIPLE_INITS
DYLD_NEW_LOCAL_SHARED_REGIONS
DYLD_NO_FIX_PREBINDING
DYLD_TRACE
DESCRIPTION
The dynamic linker uses the following environment variables. They affect any program that uses the dynamic linker.
DYLD_FRAMEWORK_PATH
This is a colon separated list of directories that contain frameworks. The dynamic linker searches these directories before it
searches for the framework by its install name. It allows you to test new versions of existing frameworks. (A framework is a
library install name that ends in the form XXX.framework/Versions/YYY/XXX or XXX.framework/XXX, where XXX and YYY are any name.)
For each framework that a program uses, the dynamic linker looks for the framework in each directory in DYLD_FRAMEWORK_PATH in turn.
If it looks in all the directories and can't find the framework, it searches the directories in DYLD_LIBRARY_PATH in turn. If it
still can't find the framework, it then searches DYLD_FALLBACK_FRAMEWORK_PATH and DYLD_FALLBACK_LIBRARY_PATH in turn.
Use the -L option to otool(1). to discover the frameworks and shared libraries that the executable is linked against.
DYLD_FALLBACK_FRAMEWORK_PATH
This is a colon separated list of directories that contain frameworks. It is used as the default location for frameworks not found
in their install path.
By default, it is set to $(HOME)/Library/Frameworks:/Library/Frameworks:/Network/Library/Frameworks:/System/Library/Frameworks
DYLD_LIBRARY_PATH
This is a colon separated list of directories that contain libraries. The dynamic linker searches these directories before it
searches the default locations for libraries. It allows you to test new versions of existing libraries.
For each library that a program uses, the dynamic linker looks for it in each directory in DYLD_LIBRARY_PATH in turn. If it still
can't find the library, it then searches DYLD_FALLBACK_FRAMEWORK_PATH and DYLD_FALLBACK_LIBRARY_PATH in turn.
Use the -L option to otool(1). to discover the frameworks and shared libraries that the executable is linked against.
DYLD_FALLBACK_LIBRARY_PATH
This is a colon separated list of directories that contain libraries. It is used as the default location for libraries not found in
their install path. By default, it is set to $(HOME)/lib:/usr/local/lib:/lib:/usr/lib.
DYLD_INSERT_LIBRARIES
This is a colon separated list of dynamic libraries to load before the ones specified in the program. This lets you test new mod-
ules of existing dynamic shared libraries that are used in flat-namespace images by loading a temporary dynamic shared library with
just the new modules. Note that this has no effect on images built a two-level namespace images using a dynamic shared library
unless DYLD_FORCE_FLAT_NAMESPACE is also used.
DYLD_FORCE_FLAT_NAMESPACE
Force all images in the program to be linked as flat-namespace images and ignore any two-level namespace bindings. This may cause
programs to fail to execute with a multiply defined symbol error if two-level namespace images are used to allow the images to have
multiply defined symbols.
DYLD_IMAGE_SUFFIX
This is set to a string of a suffix to try to be used for all shared libraries used by the program. For libraries ending in
".dylib" the suffix is applied just before the ".dylib". For all other libraries the suffix is appended to the library name. This
is useful for using conventional "_profile" and "_debug" libraries and frameworks.
DYLD_PRINT_LIBRARIES
When this is set, the dynamic linker writes to file descriptor 2 (normally standard error) the filenames of the libraries the pro-
gram is using. This is useful to make sure that the use of DYLD_LIBRARY_PATH is getting what you want.
DYLD_PRINT_LIBRARIES_POST_LAUNCH
This does the same as DYLD_PRINT_LIBRARIES but the printing starts after the program gets to its entry point.
DYLD_EBADEXEC_ONLY
When this is set, the dynamic linker does all of the work needed to launch a program without launching it. This either prints the
cause why the program could not be launched or prints a message saying the program could be launched. This variable can be used a
supplement to the program ebadexec(1) to determine why a program can't be launched. For programs that should not have any undefined
symbols when launched the DYLD_BIND_AT_LAUNCH can also be set to check this.
DYLD_BIND_AT_LAUNCH
When this is set, the dynamic linker binds all undefined symbols the program needs at launch time. This includes function symbols
that can are normally lazily bound at the time of their first call.
DYLD_DEAD_LOCK_HANG
When this is set, the dynamic linker enters a loop that hangs the program if a thread doing a dynamic linker operation attempts to
start another dynamic linker operation before completing the first. This lets you attach a debugger to the process instead of let-
ting the process exit.
DYLD_PREBIND_DEBUG
When this is set, the dynamic linker prints diagnostics about launching prebound programs and libraries. This lets you determine why
a program is not being launched prebound. You can view the recorded library time stamps with the -Lv option to otool(1).
DYLD_ABORT_MULTIPLE_INITS
When this is set, the dynamic linker causes the program to abort when multiple library initialization routines are being run which
can happen if code called via a library initialization routine makes a call to a dyld API. Then under the debugger it is easy to do
a back trace and find the code that is making the call to a dyld API via code called from a library initialization routine
For secure programs that are UNIX set uid or set gid, the dynamic linker will not use the dyld environment variables for path searching and
library insertion, unless the program is run as the real user. For secure programs, the dynamic linker clears out the value of the dyld
path and insertion environment variables. This is so that if a program is exec(2)'ed from a secure program too will not have it's
libraries searched for, as well. For statically linked secure programs that exec(2) other programs that might use the dynamic linker, they
too should clear out the values of the dyld path and insertion environment variables.
DYLD_NEW_LOCAL_SHARED_REGIONS
When set, the dynamic linker directs the system to provide a new set of shared regions as the repository for library load requests
for dynamic libraries built with MH_SPLIT_SEGS (split shared libraries).
Split shared libraries reside in a defined contiguous region of address space in all dynamic linker runtime processes. This space
is backed by named regions or sub-maps. These sub-maps are owned by the system and items which are to mapped into them must be
mapped via the load_shared_file(2) call. The use of sub-maps promotes a high degree of system resource sharing between the pro-
cesses which incorporate and use them. However, some processes require either additional or different libraries to be loaded into
the shared region. While there is some space available within the shared region for alternate and new shared libraries, it is inap-
propriate to use that area for temporary or private libraries. Setting the DYLD_NEW_LOCAL_SHARED_REGIONS flag will cause all chil-
dren of the current process to have their own set of sub-maps. In this way the libraries found in the children's submaps will not
be caused to be present in the submaps shared by the rest of the system.
DYLD_NEW_LOCAL_SHARED_REGIONS should be set by anyone wishing to run non-standard or temporary split shared libraries by setting an
explicit path to point to them. i.e. by using the DYLD_LIBRARY_PATH environment variable instead of changing the root by executing
a chroot(2) call.
DYLD_TRACE
Cause dyld to put tracing information in the kernel trace buffer for its operations.
DYLD_NO_FIX_PREBINDING
Causes dyld not to run /usr/bin/fix_prebinding on executables that are launched which had prebinding information that could not be
used for the launch.
SEE ALSO
libtool(1), ld(1), otool(1), redo_prebinding(1)
Apple Computer, Inc. July 24, 2002 DYLD(1)