NAME
ldconfig —
configure the a.out shared library
cache
SYNOPSIS
ldconfig |
[-cmrsSv] [directory
...] |
DESCRIPTION
ldconfig is used to prepare a set of
“hints” for use by the a.out run-time linker
ld.so to facilitate quick lookup of shared libraries
available in multiple directories. ldconfig is only
available on systems that use the “a.out” format for executables
and libraries – on ELF systems, all the work is done by
ld.elf_so.
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:
-c- Do not scan directories listed in /etc/ld.so.conf for shared libraries.
-m- Merge the result of the scan of the directories given as arguments into the existing hints file. The default action is to build the hints file afresh.
-r- Lists the current contents of ld.so.hints on the standard output. The hints file will not be modified.
-s- Do not scan the built-in system directory (/usr/lib), nor any directories listed in /etc/ld.so.conf for shared libraries.
-S- Do not scan the built-in system directory (/usr/lib), for shared libraries. (Directories listed in /etc/ld.so.conf are still scanned.)
-v- Switch on verbose mode.
FILES
/var/run/ld.so.hints, /etc/ld.so.conf
SEE ALSO
HISTORY
A ldconfig utility first appeared in SunOS
4.0, it appeared in its current form in NetBSD
0.9A.
SECURITY CONSIDERATIONS
Special care must be taken when loading shared libraries into the
address space of
set-user-ID
programs. Whenever such a program is run, ld.so will
only load shared libraries from the 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.