By default, it scans a set of built-in system directories,
directories listed in
/etc/ld.so.conf
,
and any
directories
specified on the command line (in the given order) looking for shared
libraries and stores the results in the file
/var/run/ld.so.hints
to forestall the overhead that would otherwise result from the
directory search operations
ld.so
would have to perform to load required shared libraries.
The shared libraries so found will be automatically available for loading if needed by the program being prepared for execution. This obviates the need for storing search paths within the executable.
The
LD_LIBRARY_PATH
environment variable can be used to override the use of
directories (or the order thereof) from the cache or to specify additional
directories where shared libraries might be found.
LD_LIBRARY_PATH
is a
`:'
separated list of directory paths that are searched by
ld.so
when it needs to load a shared library.
It can be viewed as the run-time equivalent of the
-L
switch of
ld.
ldconfig is typically run as part of the boot sequence.
The following options are recognized by ldconfig:
/etc/ld.so.conf
for shared libraries.
ld.so.hints
on the standard output.
The hints file will not be modified.
/usr/lib
),
nor any directories listed in
/etc/ld.so.conf
for shared libraries.
/usr/lib
),
for shared libraries.
(Directories listed in
/etc/ld.so.conf
are still scanned.)
/var/run/ld.so.hints
,
/etc/ld.so.conf
ld.so.hints
file.
In particular, the
LD_LIBRARY_PATH
and
LD_PRELOAD
is not used to search for libraries.
Thus, the role of ldconfig is dual.
In addition to building a set of hints for quick lookup, it also serves to
specify the trusted collection of directories from which shared objects can
be safely loaded.
It is presumed that the set of directories specified to
ldconfig
is under control of the system's administrator.
ld.so
further assists set-user-ID programs by erasing the
LD_LIBRARY_PATH
and
LD_PRELOAD
from the environment.