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- Prebind safely: always copies the binaries when prebind information is
added to a file. Use this to eliminate the possibility that
ETXTBUSYwill occur when attempting to run a binary whilst prebinding. -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
When prebind 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.
Prebind information adds a small amount of data to the end of each specified
program and associated shared libraries. Prebinding is loosely based on an
earlier concept called prelinking, which also accelerated
ld.so(1) performance but simultaneously impaired address space
randomization.
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
HISTORY
An ldconfig utility first appeared in
SunOS 4.0. It appeared in its current form in NetBSD
0.9A.