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LD.SO(8)                    System Manager's Manual                   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 /usr/lib, and then /lib.

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

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.
       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).



                                 14 March 1998                        LD.SO(8)