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RTLD(1)			  BSD 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 de-
     termine 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	be-
     gins.  This is useful for C++ libraries that contain static constructors.

     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 ig-
		      nored 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 li-
		      braries.	If the directory is not	specified then the di-
		      rectories	specified by LD_LIBRARY_PATH will be searched
		      first followed by	the set	of built-in standard directo-
		      ries.  This is ignored for set-user-ID and set-group-ID

     LD_BIND_NOW      When set to a nonempty string, causes	to re-
		      locate all external function calls before	starting exe-
		      cution 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 ob-
		      jects, to	standard output.

		      When set to a nonempty string, causes	to ex-
		      pand 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)

BSD			       January 28, 2000				   BSD


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