LD.SO(8)							      LD.SO(8)



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

DESCRIPTION
       ld.so loads the shared libraries needed by a program, prepares the pro-
       gram to run, and then runs it.  Unless  explicitly  specified  via  the
       -static	option to ld during compilation, all Linux programs are incom-
       plete and require further linking at run time.

       The necessary shared libraries needed by the program are  searched  for
       in the following order

       o      Using	 the	  environment	  variable     LD_LIBRARY_PATH
	      (LD_AOUT_LIBRARY_PATH for a.out programs).  Except if  the  exe-
	      cutable  is a setuid/setgid binary, in which case it is ignored.

       o      From the cache file /etc/ld.so.cache which contains  a  compiled
	      list  of	candidate  libraries previously found in the augmented
	      library path.

       o      In the default path /lib, and then /usr/lib.

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
       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	setuid/setgid  ELF binaries, only libraries in
	      the standard search directories that are	also  setgid  will  be
	      loaded.

       LD_TRACE_LOADED_OBJECTS
	      If  present,  causes  the  program  to  list its dynamic library
	      dependencies, as if run by ldd, instead of running normally.

       LD_BIND_NOW
	      If present, causes the dynamic linker to resolve all symbols  at
	      program startup instead of when they are first referenced.

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

       LD_AOUT_LIBRARY_PATH
	      A colon-separated list of directories in	which  to  search  for
	      a.out libraries at execution-time.  Similar to the PATH environ-
	      ment variable.

       LD_AOUT_PRELOAD
	      The name of an additional, user-specified, a.out shared  library
	      to  be loaded after all others.  This can be used to selectively
	      override functions in other shared libraries.

       LD_NOWARN
	      Suppress warnings about a.out libraries with incompatible  minor
	      version numbers.

       LD_WARN
	      If set to non-empty string, warn about unresolved symbols.

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

       LD_DEBUG
	      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  categories  can  be
	      specified in this environment variable.

       LD_DEBUG_OUTPUT
	      File  where LD_DEBUG output should be fed into, default is stan-
	      dard output. LD_DEBUG_OUTPUT is ignored for setuid/setgid  bina-
	      ries.

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

       LD_PROFILE
	      Shared object to be profiled.

       LD_PROFILE_OUTPUT
	      File where LD_PROFILE output should be stored, default is  stan-
	      dard  output. LD_DEBUG_OUTPUT is ignored for setuid/setgid bina-
	      ries.

       LD_ASSUME_KERNEL
	      Every DSO (Dynamic Shared Object, aka shared library)  can  tell
	      the  dynamic  linker  in	glibc  which minimum OS ABI version is
	      needed. The information about the  minimum  OS  ABI  version  is
	      encoded  in a ELF note section usually named .note.ABI-tag. This
	      is used to determine which library to load when multiple version
	      of   the	 same	library  is  installed	on  the  system.   The
	      LD_ASSUME_KERNEL environment variable overrides the kernel  ver-
	      sion  used  by  the dynamic linker to determine which library to
	      load.

RPATH TOKEN EXPANSION
       The runtime linker provides a number of tokens that can be used	in  an
       rpath specification (DT_RPATH or DT_RUNPATH).

       $ORIGIN
	      ld.so understands the string $ORIGIN (or equivalently ${ORIGIN})
	      in an rpath specification to mean the directory  containing  the
	      application   executable.   Thus,   an  application  located  in
	      somedir/app  could  be  compiled	with   gcc   -Wl,-rpath,'$ORI-
	      GIN/../lib'  so  that  it  finds an associated shared library in
	      somedir/lib no matter where somedir is located in the  directory
	      hierarchy.

       $PLATFORM
	      The  string  $PLATFORM (or equivalently ${PLATFORM}) in an rpath
	      specifcation expands  to	the  processor	type  of  the  current
	      machine. Please note that on some architectures the Linux kernel
	      doesn't provide a platform string to the dynamic linker.

       $LIB   The string $LIB (or equivalently ${LIB}) in an rpath corresponds
	      to  the system libraries directory, which is /lib for the native
	      architecture on FHS compliant GNU/Linux systems.

FILES
       /lib/ld.so	   a.out dynamic linker/loader
       /lib/ld-linux.so.*  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.
			   libraries  and  an  ordered	 list	of   candidate
			   libraries.
       /etc/ld.so.nohwcap  When  this  file is present the dynamic linker will
			   load the non-optimized version of a	library,  even
			   if the CPU supports the optimized version.
       lib*.so* 	   shared libraries

SEE ALSO
       ldd(1), ldconfig(8).

BUGS
       Currently  ld.so has no means of unloading and searching for compatible
       or newer version of libraries.

       ld.so functionality is only available for  executables  compiled  using
       libc version 4.4.3 or greater.

AUTHORS
       David  Engel,  Eric  Youngdale, Peter MacDonald, Hongjiu Lu, Linus Tor-
       valds, Lars Wirzenius  and  Mitch  D'Souza  (not  necessarily  in  that
       order).



				  26 May 2007			      LD.SO(8)