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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

     When resolving dependencies for the loaded objects,
     translates dynamic token strings in rpath and soname.  If the -z origin
     option of the static linker was set when linking the binary, the token
     expansion is performed at the object load time, see 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

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

     $PLATFORM      Translated to the machine hardware platform.

     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.  The
     following search order is used to locate required shared objects:

           1.   DT_RPATH of the referencing object unless that object also
                contains a DT_RUNPATH tag
           2.   DT_RPATH of the program unless the referencing object contains
                a DT_RUNPATH tag
           3.   Path indicated by LD_LIBRARY_PATH environment variable
           4.   DT_RUNPATH of the referencing object
           5.   Hints file produced by the ldconfig(8) utility
           6.   The /lib and /usr/lib directories, unless the referencing
                object was linked using the ``-z nodefaultlib'' option

     The 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_DUMP_REL_POST       If set, will print a table containing
                            all relocations after symbol binding and

     LD_DUMP_REL_PRE        If set, will print a table containing
                            all relocations before symbol binding and

     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_LIBRARY_PATH_RPATH  If the variable is specified and has a value
                            starting with any of 'y', 'Y' or '1' symbols, the
                            path specified by LD_LIBRARY_PATH variable is
                            allowed to override the path from DT_RPATH for
                            binaries which does not contain DT_RUNPATH tag.
                            For such binaries, when the variable
                            LD_LIBRARY_PATH_RPATH is set, ``-z nodefaultlib''
                            link-time option is ignored as well.

     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_LIBRARY_PATH_FDS A colon separated
                            list of file descriptor numbers for library
                            directories.  This is intended for use within
                            capsicum(4) sandboxes, when global namespaces such
                            as the filesystem are unavailable.  It is
                            consulted just after LD_LIBRARY_PATH.  This
                            variable is unset for set-user-ID and set-group-ID

     LD_BIND_NOT            When set to a nonempty string, prevents
                            modifications of the PLT slots when doing
                            bindings.  As result, each call of the PLT-
                            resolved function is resolved.  In combination
                            with debug output, this provides complete account
                            of all bind actions at runtime.  This variable is
                            unset 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

                            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.  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

                            %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

                            %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, will log events such as the
                            loading and unloading of shared objects via

     LD_LOADFLTR            If set, 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

DIRECT EXECUTION MODE is typically used implicitly, loaded by the kernel as
     requested by the PT_INTERP program header of the executed binary.
     FreeBSD also supports a direct execution mode for the dynamic linker.  In
     this mode, the user explicitly executes and provides the path
     of the program to be linked and executed as an argument.  This mode
     allows use of a non-standard dynamic linker for a program activation
     without changing the binary or without changing the installed dynamic
     linker.  Execution options may be specified.

     The syntax of the direct invocation is

           /libexec/ [-f fd] [-p] [--] image_path [image arguments]

     The options are as follows:

     -f fd   File descriptor fd references the binary to be activated by
     It must already be opened in the process when
             executing  If this option is specified, image_path
             is only used to provide the argv[0] value to the program.

     -p      If the image_path argument specifies a name which does not
             contain a slash ``/'' character, uses the search path
             provided by the environment variable PATH to find the binary to

     --      Ends the options.  The argument following -- is
             interpreted as the path of binary to execute.

     To conform to user expectation to not break some naively restricted
     execution environments, in the direct execution mode emulates
     verification of the binary execute permission for current user.  The
     verification only uses Unix DACs, ignores ACLs and is racy by its nature.
     The environments which rely on such restrictions are weak and breakable
     on its own.

     /var/run/        Hints file.
     /var/run/      Hints file for 32-bit binaries on 64-bit
     /etc/libmap.conf                The libmap configuration file.
     /etc/libmap32.conf              The libmap configuration file for 32-bit
                                     binaries on 64-bit system.

     ld(1), ldd(1), capsicum(4), elf(5), libmap.conf(5), ldconfig(8)

FreeBSD 11.1-RELEASE-p4          May 20, 2017          FreeBSD 11.1-RELEASE-p4
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