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.