LDCONFIG(8)

NAME
ldconfig - configure the shared library cache

SYNOPSIS
ldconfig [-DmPRrSsUv] [path ...]

DESCRIPTION
ldconfig is used to prepare a set of “hints” for use by the run-time linker ld.so(1) to facilitate quick lookup of shared libraries available in multiple directories. It scans a set of built-in system directories 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(1) would have to perform to load the 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 which are searched by ld.so(1) when it needs to load a shared library. It can be viewed as the run-time equivalent of the -L switch of ld(1).

ldconfig is typically run as part of the boot sequence. In addition to the built-in system directories, directories containing shared libraries may be specified via the shlib_dirs variable in /etc/rc.conf.local. See rc.conf(8) for further information.

The following options are recognized by ldconfig:

-D  Remove any prebind information in the specified binary or shared library.

-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. This option cannot be used with -U.

-P  Create and append prebind information to all executables found in the specified directories, and also all shared libraries which are required by those executables.

-R  Rescan the previously configured directories. This opens the hints file and fetches the directory list from the header. Any additional pathnames on the command line are also processed.

-r  List the current contents of ld.so.hints on the standard output. The hints file will not be modified.

-S  Perform prelinking operations in a safe mode; always copies the binaries when prelinking data is added to a file. Use this to eliminate the possibility that ETXTBUSY will occur when attempting to run a binary while prelinking is running.

-s  Do not scan the built-in system directory (“/usr/lib”) for shared libraries.

-U  Unconfigure directories specified on the command line or remove inaccessible directories from search path if no directories specified. This option cannot be used with -m.

-v  Switch on verbose mode.

PREBINDING
Prebinding is loosely based on an earlier concept called Prelinking, which also accelerated ld.so(1) performance but simultaneously impaired address space randomization. When prebinding information is added to libraries and programs using -P, program startup can be significantly improved because ld.so(1) can initialize the shared library environment much faster. Prebinding information adds a small amount of data to the end of each specified program and associated shared libraries.

SECURITY
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(1) will only load shared libraries from the ld.so.hints file. In particular, the LD_LIBRARY_PATH 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 are under control of the system's administrator. ld.so(1) further assists set-user-Id programs by erasing the LD_LIBRARY_PATH from the environment.

ENVIRONMENT

LD_LIBRARY_PATH
    Additional directories containing shared libraries, settable in the user's environment.

shlib_dirs
    Additional directories containing shared libraries, settable in /etc/rc.conf.local.

FILES
/etc/rc.conf
/etc/rc.conf.local
/var/run/ld.so.hints

SEE ALSO
ld(1), elf(5), rc.conf(8)

HISTORY
An ldconfig utility first appeared in SunOS 4.0. It appeared in its current form in NetBSD 0.9a.