NAME
ldconfig —
configure the shared library
cache
SYNOPSIS
ldconfig |
[-elf] [-Rimr]
[-f hints_file]
[directory | file ...] |
DESCRIPTION
Theldconfig utility is used to prepare a set of
“hints” for use by the dynamic linker 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 a system file to forestall the overhead
that would otherwise result from the directory search operations the dynamic
linker would have to perform to load the required shared libraries.
Alternatively, files may be specified; these
are expected to contain directories to scan for shared libraries. Each
directory's pathname must start on a new line. Blank lines and lines
starting with the comment character
‘#’ are ignored. Filenames must
conform to the lib*.so.[0-9] pattern in order to be
added to the hints file.
For security reasons, directories which are world or
group-writable or which are not owned by root produce warning messages and
are skipped, unless the -i option is present.
The shared libraries which are 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 the dynamic linker
when it needs to load a shared library. It can be viewed as the run-time
equivalent of the -L switch of
ld(1).
The ldconfig utility is typically run as
part of the boot sequence.
The following options are recognized by
ldconfig:
-elf- Generate the hints for ELF format shared libraries.
-R- Rescan the previously configured directories. This opens the previous hints file and fetches the directory list from the header. Any additional pathnames on the command line are also processed. This is the default action when no parameters are given.
-fhints_file- Read and/or update the specified hints file, instead of the standard file. This option is provided primarily for testing.
-i- Run in insecure mode. The security checks will not be performed.
-m- Instead of replacing the contents of the hints file with those found in
the directories specified, “merge” in new entries.
Directories recorded in the hints file by previous runs of
ldconfigare also rescanned for new shared libraries. -r- List the current contents of the hints file on the standard output. The hints file is not modified. The list of directories stored in the hints file is included.
-s- Ignored for compatibility with other operating systems.
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 by any user except the owner of the program, the dynamic
linker will only load shared libraries from the 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.
FILES
- /var/run/ld-elf.so.hints
- Standard hints file for the ELF dynamic linker.
- /etc/ld-elf.so.conf
- Conventional configuration file containing directory names for invocations
with
-elf.
SEE ALSO
HISTORY
A ldconfig utility first appeared in SunOS
4.0, it appeared in its current form in FreeBSD
1.1.