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RTLD(1)                 FreeBSD General Commands Manual                RTLD(1)

NAME, rtld - run-time link-editor

     The utility is a self-contained shared object providing run-
     time support for loading and link-editing shared objects into a process'
     address space.  It is also commonly known as the dynamic linker.  It uses
     the data structures contained within dynamically linked programs to
     determine which shared libraries are needed and loads them using the
     mmap(2) system call.

     After all shared libraries have been successfully loaded,
     proceeds to resolve external references from both the main program and
     all objects loaded.  A mechanism is provided for initialization routines
     to be called on a per-object basis, giving a shared object an opportunity
     to perform any extra set-up before execution of the program proper
     begins.  This is useful for C++ libraries that contain static

     The utility itself is loaded by the kernel together with any
     dynamically-linked program that is to be executed.  The kernel transfers
     control to the dynamic linker.  After the dynamic linker has finished
     loading, relocating, and initializing the program and its required shared
     objects, it transfers control to the entry point of the program.

     To locate the required shared objects in the file system, may
     use a ``hints'' file prepared by the ldconfig(8) utility.

     The utility recognizes a number of environment variables that
     can be used to modify its behaviour as follows:

     LD_LIBRARY_PATH      A colon separated list of directories, overriding
                          the default search path for shared libraries.  This
                          is ignored for set-user-ID and set-group-ID

     LD_PRELOAD           A list of shared libraries, separated by colons
                          and/or white space, to be linked in before any other
                          shared libraries.  If the directory is not specified
                          then the directories specified by LD_LIBRARY_PATH
                          will be searched first followed by the set of built-
                          in standard directories.  This is ignored for set-
                          user-ID and set-group-ID programs.

     LD_BIND_NOW          When set to a nonempty string, causes to
                          relocate all external function calls before starting
                          execution of the program.  Normally, function calls
                          are bound lazily, at the first call of each
                          function.  LD_BIND_NOW increases the start-up time
                          of a program, but it avoids run-time surprises
                          caused by unexpectedly undefined functions.

                          When set to a nonempty string, causes to
                          exit after loading the shared objects and printing a
                          summary which includes the absolute pathnames of all
                          objects, to standard output.

                          When set to a nonempty string, causes to
                          expand the summary to indicate which objects caused
                          each object to be loaded.


                          When set, these variables are interpreted as format
                          strings a la printf(3) to customize the trace output
                          and are used by ldd(1)'s -f option and allows ldd(1)
                          to be operated as a filter more conveniently.  The
                          following conversions can be used:

                          %a    The main program's name (also known as

                          %A    The value of the environment variable

                          %o    The library name.

                          %m    The library's major version number.

                          %p    The full pathname as determined by rtld's
                                library search rules.

                          %x    The library's load address.

                          Additionally, `\n' and `\t' are recognized and have
                          their usual meaning.


     ld(1), ldd(1), elf(5), ldconfig(8)

FreeBSD 11.0-PRERELEASE        January 28, 2000        FreeBSD 11.0-PRERELEASE


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