ld.so

Sommaire

NAME

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

DESCRIPTION

ld.so loads the shared libraries needed by a program, prepares the program to run, and then runs it. Unless explicitly specified via the -static option to ld during compilation, all Linux programs are incomplete 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 executable 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 environment 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 Torvalds, Lars Wirzenius and Mitch D'Souza (not necessarily in that order).