DYLD(1)DYLD(1)NAMEdyld - the dynamic link editor
SYNOPSIS
DYLD_LIBRARY_PATH
DYLD_INSERT_LIBRARIES
DYLD_PRINT_LIBRARIES
DYLD_MEM_PROTECT
DYLD_EBADEXEC_ONLY
DYLD_BIND_AT_LAUNCH
DYLD_DEAD_LOCK_HANG
DYLD_PREBIND_DEBUG
DESCRIPTION
These environment variables are used by the dynamic link editor and
when set effect programs that use the dynamic link editor.
DYLD_LIBRARY_PATH
This is set to a colon separated list of directories to change
which libraries a program uses. Then for each library install
name recorded in the executable, bundles and dependent libraries
the program uses, the last component of the install name is
appended with each of the directories in DYLD_LIBRARY_PATH in
turn. The first file that is found is then used for the
library. If none is found then the install name as recorded is
used. This allows such things as testing new versions of
existing dynamic shared libraries. The recorded library install
name can be seen with the -L option to otool(1).
DYLD_INSERT_LIBRARIES
This is set to a colon separated list of dynamic library
filenames to add additional libraries to a program when run.
The libraries listed in the list are loaded before the libraries
recorded in the executable, bundles and dependent libraries.
This allows such things as testing new modules of existing
dynamic shared libraries by creating a temporary dynamic shared
library with just the new modules.
DYLD_PRINT_LIBRARIES
When this is set the dynamic link editor writes to file
descriptor 2 (normally standard error) the filenames of the
libraries the program is using. This is useful to make sure
that the use of DYLD_LIBRARY_PATH is getting what you want.
DYLD_MEM_PROTECT
When this is set it causes the dynamic link editor to change the
protection of the memory it uses for its data structures when it
is not operating on them. It is possible for an errant program
to mistakenly write on the data structures of dynamic link
editor. This is used to help track down the point the program
does it's mistaken write. This will then cause the program to
crash at the first occurrence of a write making the error easier
to track down. Unfortunately this can't be done in the debugger
as the debugger's interface to the dynamic link editor will
cause the dynamic link editor's memory to remain writable. But
can produce a very useful core file.
DYLD_EBADEXEC_ONLY
When this is set it causes the dynamic link editor to do all of
the work needed to launch the program without launching it.
This will either print the cause why the program could not be
launch or print a message saying the program could be launched.
This 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 (see below).
DYLD_BIND_AT_LAUNCH
When this is set it causes the dynamic link editor to bind 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 it causes the dynamic link editor to enter a
loop that hangs the program if a thread doing a dynamic link
editor operation attempts to start another dynamic link editor
operation before completing the first. This allows a debugger
to be attached to such processes instead of letting this error
to cause the program to exit so the problem can be fixed.
DYLD_PREBIND_DEBUG
When set it causes the dynamic link editor to print diagnostics
as to the launching of programs and libraries build prebound.
This allows determining why a program is not being launch
prebound. The recorded library time stamps can be seen with the
-Lv option to otool(1).
For secure programs that are UNIX set uid or set gid, the searching of
libraries with the environment variable and the insertion of libraries
will not be done, unless the program is run as the real user. For
secure programs the dynamic link editor clears out the value of
DYLD_LIBRARY_PATH. This is so that if a program is exec(2)'ed from a
secure program it too will not have it's libraries searched for. For
staticly linked secure programs that exec(2) other programs that might
being using the dynamic link editor they too should clear out the value
of DYLD_LIBRARY_PATH.
SEE ALSOlibtool(1), ld(1), otool(1), redo_prebinding(1)NeXT Software, Inc. March 28, 1996 DYLD(1)
