is a self-contained, position
independent program image providing run-time support for loading and
link-editing shared objects into a process's address space. It uses the data
structures (see elf(5)
within dynamically linked programs to determine which shared libraries are
needed and loads them at a convenient virtual address using the
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 begins.
is itself a shared object that is
initially loaded by the kernel.
To quickly locate the required shared objects in the filesystem,
may use a “hints” file,
prepared by the ldconfig(8)
utility, in which the full path specification of the shared objects can be
looked up by hashing on the 3-tuple ⟨library-name,
recognises a number of environment
variables that can be used to modify its behaviour as follows:
- A colon separated list of directories, prepending the default search path
for shared libraries. This variable is ignored for set-user-ID and
- A colon separate list of library names to load before any of the regular
libraries are loaded. This variable is ignored for set-user-ID and
- Specifies that the dynamic linker should process all relocations before
transferring control to the program. Normally, the procedure linkage table
entries are handled lazily, avoiding symbol lookup and relocation for
unused functions. This variable is ignored for set-user-ID and
- When set, causes
ld.so to exit after
loading the shared objects and printing a summary which includes the
absolute pathnames of all objects, to standard output.
- When set, these variables are interpreted as format strings a la
printf(3) to customize the
trace output and are used by
-f option and allows
ldd(1) to be operated as a
filter more conveniently.
LD_TRACE_LOADED_OBJECTS_FMT1 is used
for tracing shared libraries;
dynamically loaded objects, the dynamic linker, and the main executable.
The following conversions can be used:
Additionally, \n and
\t are recognised and have their usual
- The main program's name (also known as
- The value of the environment variable
- The end address of the object.
- The object's group reference count.
- The object's major version number.
- The object's minor version number.
- The object's open count.
- The object name.
- The full pathname as determined by
ld.so's library search rules.
- The object's reference count.
- The object's load address.
- When set, be verbose about what
- library location hints built by
The shared library model employed first appeared in SunOS 4.0.