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
ld(1),
ld.so(1),
ld.so.conf(5),
link(5)
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.