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

NAME
     ld-elf.so.1, ld.so, rtld - run-time link-editor

DESCRIPTION
     The ld-elf.so.1 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, ld-elf.so.1
     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
     constructors.

     When resolving dependencies for the loaded objects, ld-elf.so.1 may be
     allowed to translate dynamic token strings in rpath and soname by setting
     -z origin option of the static linker ld(1).  The following strings are
     recognized now:

     $ORIGIN        Translated to the full path of the loaded object.

     $OSNAME        Translated to the name of the operating system
                    implementation.

     $OSREL         Translated to the release level of the operating system.

     $PLATFORM      Translated to the machine hardware platform.

     The ld-elf.so.1 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, ld-elf.so.1 may
     use a ``hints'' file prepared by the ldconfig(8) utility.

     The ld-elf.so.1 utility recognizes a number of environment variables that
     can be used to modify its behaviour.  On 64-bit architectures, the linker
     for 32-bit objects recognizes all the environment variables listed below,
     but is being prefixed with LD_32_, for example:
     LD_32_TRACE_LOADED_OBJECTS.

     LD_DUMP_REL_POST       If set, ld-elf.so.1 will print a table containing
                            all relocations after symbol binding and
                            relocation.

     LD_DUMP_REL_PRE        If set, ld-elf.so.1 will print a table containing
                            all relocations before symbol binding and
                            relocation.

     LD_LIBMAP              A library replacement list in the same format as
                            libmap.conf(5).  For convenience, the characters
                            `=' and `,' can be used instead of a space and a
                            newline.  This variable is parsed after
                            libmap.conf(5), and will override its entries.
                            This variable is unset for set-user-ID and set-
                            group-ID programs.

     LD_LIBMAP_DISABLE      If set, disables the use of libmap.conf(5) and
                            LD_LIBMAP.  This variable is unset for set-user-ID
                            and set-group-ID programs.

     LD_ELF_HINTS_PATH      This variable will override the default location
                            of ``hints'' file.  This variable is unset for
                            set-user-ID and set-group-ID programs.

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

     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
                            variable is unset for set-user-ID and set-group-ID
                            programs.

     LD_BIND_NOW            When set to a nonempty string, causes ld-elf.so.1
                            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.

     LD_TRACE_LOADED_OBJECTS
                            When set to a nonempty string, causes ld-elf.so.1
                            to exit after loading the shared objects and
                            printing a summary which includes the absolute
                            pathnames of all objects, to standard output.

     LD_TRACE_LOADED_OBJECTS_ALL
                            When set to a nonempty string, causes ld-elf.so.1
                            to expand the summary to indicate which objects
                            caused each object to be loaded.

     LD_TRACE_LOADED_OBJECTS_FMT1

     LD_TRACE_LOADED_OBJECTS_FMT2
                            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.  If the dependency name starts with
                            string lib, LD_TRACE_LOADED_OBJECTS_FMT1 is used,
                            otherwise LD_TRACE_LOADED_OBJECTS_FMT2 is used.
                            The following conversions can be used:

                            %a    The main program's name (also known as
                                  ``__progname'').

                            %A    The value of the environment variable
                                  LD_TRACE_LOADED_OBJECTS_PROGNAME.  Typically
                                  used to print both the names of programs and
                                  shared libraries being inspected using
                                  ldd(1).

                            %o    The library name.

                            %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_UTRACE              If set, ld-elf.so.1 will log events such as the
                            loading and unloading of shared objects via
                            utrace(2).

     LD_LOADFLTR            If set, ld-elf.so.1 will process the filtee
                            dependencies of the loaded objects immediately,
                            instead of postponing it until required.
                            Normally, the filtees are opened at the time of
                            the first symbol resolution from the filter
                            object.

FILES
     /var/run/ld-elf.so.hints        Hints file.
     /var/run/ld-elf32.so.hints      Hints file for 32-bit binaries on 64-bit
                                     system.
     /etc/libmap.conf                The libmap configuration file.
     /etc/libmap32.conf              The libmap configuration file for 32-bit
                                     binaries on 64-bit system.

SEE ALSO
     ld(1), ldd(1), elf(5), libmap.conf(5), ldconfig(8)

FreeBSD 11.0-PRERELEASE          April 1, 2009         FreeBSD 11.0-PRERELEASE

NAME | DESCRIPTION | FILES | SEE ALSO

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