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LD.SO(8)		   Linux Programmer's Manual		      LD.SO(8)



NAME
       ld.so, ld-linux.so* - dynamic linker/loader

DESCRIPTION
       The  programs ld.so and ld-linux.so* find and load the shared libraries
       needed by a program, prepare the program to run, and then run it.

       Linux binaries require dynamic linking (linking at run time) unless the
       -static option was given to ld during compilation.

       The  program  ld.so handles a.out binaries, a format used long ago; ld-
       linux.so* handles ELF (/lib/ld-linux.so.1 for libc5, /lib/ld-linux.so.2
       for  glibc2),  which everybody has been using for years now.  Otherwise
       both have the same behaviour, and use the same support files  and  pro-
       grams ldd(1), ldconfig(8) and /etc/ld.so.conf.

       The  shared libraries needed by the program are searched for in various
       places:

       o      (ELF only) Using the DT_RPATH dynamic section attribute  of  the
	      binary  if present and DT_RUNPATH attribute does not exist.  Use
	      of DT_RPATH is deprecated.

       o      Using the environment variable LD_LIBRARY_PATH.  Except  if  the
	      executable  is  a set-user-ID/set-group-ID binary, in which case
	      it is ignored.

       o      (ELF only) Using the DT_RUNPATH dynamic section attribute of the
	      binary if present.

       o      From  the	 cache file /etc/ld.so.cache which contains a compiled
	      list of candidate libraries previously found  in	the  augmented
	      library  path.  If, however, the binary was linked with -z node-
	      flib linker option, libraries in the default library  paths  are
	      skipped.

       o      In  the default path /lib, and then /usr/lib.  If the binary was
	      linked with -z nodeflib linker option, this step is skipped.

SYNOPSIS
       The dynamic linker can be run either indirectly	through	 running  some
       dynamically  linked  program  or library (in which case no command line
       options to the dynamic linker can be passed and, in the ELF  case,  the
       dynamic linker which is stored in the .interp section of the program is
       executed) or directly by running:

       /lib/ld-linux.so.*  [OPTIONS] [PROGRAM [ARGUMENTS]]

COMMAND LINE OPTIONS
       --list List all dependencies and how they are resolved.

       --verify
	      Verify that program  is  dynamically  linked  and	 this  dynamic
	      linker can handle it.

       --library-path PATH
	      Override	 LD_LIBRARY_PATH  environment  variable	 setting  (see
	      below).

       --ignore-rpath LIST
	      Ignore RPATH and RUNPATH information in object  names  in	 LIST.
	      This  option  has	 been  supported by glibc2 for about one hour.
	      Then it was renamed into:

       --inhibit-rpath LIST

ENVIRONMENT
       There are four important environment variables.

       LD_LIBRARY_PATH
	      A colon-separated list of directories in which to search for ELF
	      libraries	 at  execution-time.   Similar to the PATH environment
	      variable.

       LD_PRELOAD
	      A whitespace-separated list of additional,  user-specified,  ELF
	      shared  libraries	 to  be loaded before all others.  This can be
	      used  to	selectively  override  functions   in	other	shared
	      libraries.   For	set-user-ID/set-group-ID  ELF  binaries,  only
	      libraries in the standard search directories that are also  set-
	      user-ID will be loaded.

       LD_BIND_NOW
	      (libc5;  glibc  since  2.1.1) If set to non-empty string, causes
	      the dynamic linker to resolve all	 symbols  at  program  startup
	      instead  of  deferring  function call resolval to the point when
	      they are first referenced.  This is useful when using  a	debug-
	      ger.

       LD_TRACE_LOADED_OBJECTS
	      (ELF  only)  If  set  to non-empty string, causes the program to
	      list its dynamic library dependencies,  as  if  run  by  ldd(1),
	      instead of running normally.

       Then there are lots of more or less obscure variables, many obsolete or
       only for internal use.

       LD_WARN
	      (ELF only)(glibc since 2.1.3) If set to non-empty	 string,  warn
	      about unresolved symbols.

       LD_NOWARN
	      (a.out only)(libc5) Suppress warnings about a.out libraries with
	      incompatible minor version numbers.

       LD_BIND_NOT
	      (glibc since 2.1.95) Do not update the GOT (global offset table)
	      and PLT (procedure linkage table) after resolving a symbol.

       LD_DEBUG
	      (glibc since 2.1) Output verbose debugging information about the
	      dynamic linker.  If set to all prints all debugging  information
	      it  has,	if set to help prints a help message about which cate-
	      gories can be specified in this environment variable.

       LD_DEBUG_OUTPUT
	      (glibc since 2.1) File where LD_DEBUG output should be fed into,
	      default is standard output.  LD_DEBUG_OUTPUT is ignored for set-
	      user-ID/set-group-ID binaries.

       LD_VERBOSE
	      (glibc since 2.1) If set to non-empty string, output symbol ver-
	      sioning  information  about  the program if querying information
	      about the program (ie. either LD_TRACE_LOADED_OBJECTS  has  been
	      set,  or	--list	or  --verify  options  have  been given to the
	      dynamic linker).

       LD_PROFILE
	      (glibc since 2.1) Shared object to be profiled.

       LD_PROFILE_OUTPUT
	      (glibc since 2.1) File where LD_PROFILE output should be stored,
	      default  is  standard  output.  LD_PROFILE_OUTPUT is ignored for
	      set-user-ID/set-group-ID binaries.

       LD_AOUT_LIBRARY_PATH
	      (libc5) Version of LD_LIBRARY_PATH for a.out binaries only.  Old
	      versions of ld-linux.so.1 also supported LD_ELF_LIBRARY_PATH.

       LD_AOUT_PRELOAD
	      (libc5) Version of LD_PRELOAD for a.out binaries only.  Old ver-
	      sions of ld-linux.so.1 also supported LD_ELF_PRELOAD.

       LD_SHOW_AUXV
	      (glibc since 2.1) Show auxiliary array passed up from  the  ker-
	      nel.

       LD_HWCAP_MASK
	      (glibc since 2.1) Mask for hardware capabilities.

       LD_ORIGIN_PATH
	      (glibc  since  2.1) Path where the binary is found (for non-set-
	      user-ID programs).

       LD_DYNAMIC_WEAK
	      (glibc  since  2.1.91)  Allow  weak  symbols  to	be  overridden
	      (reverting to old glibc behaviour).

       LD_KEEPDIR
	      (a.out  only)(libc5)  Don't ignore the directory in the names of
	      a.out libraries to be loaded.  Use of this  option  is  strongly
	      discouraged.

       LDD_ARGV0
	      (libc5) argv[0] to be used by ldd(1) when none is present.

FILES
       /lib/ld.so
	      a.out dynamic linker/loader
       /lib/ld-linux.so.{1,2}
	      ELF dynamic linker/loader
       /etc/ld.so.cache
	      File  containing	a  compiled  list  of  directories in which to
	      search for libraries and an ordered list of candidate libraries.
       /etc/ld.so.preload
	      File  containing	a  whitespace  separated  list	of  ELF shared
	      libraries to be loaded before the program.
       lib*.so*
	      shared libraries

NOTES
       The ld.so functionality is available  for  executables  compiled	 using
       libc  version  4.4.3  or greater.  ELF functionality is available since
       Linux 1.1.52 and libc5.

SEE ALSO
       ldd(1), ldconfig(8)



				  2001-12-16			      LD.SO(8)
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