LDCONFIG(8)

NAME
ldconfig - configure the shared library cache

SYNOPSIS
ldconfig [-32] [-aout | -elf] [-Rimrsv] [-f hints_file] [directory | file ...]

DESCRIPTION
The ldconfig 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.

Files named on the command line 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:

-32 Generate the hints for 32-bit ABI shared libraries on 64-bit systems that support running 32-bit binaries.

-aout
    Generate the hints for a.out format shared libraries.

-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.

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

-v  Switch on verbose mode.

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.so.hints
    Standard hints file for the a.out dynamic linker.
/var/run/ld-elf.so.hints
    Standard hints file for the ELF dynamic linker.
/etc/ld.so.conf
    Conventional configuration file containing directory names for invocations with -aout.
/etc/ld-elf.so.conf
    Conventional configuration file containing directory names for invocations with -elf.
/var/run/ld-elf32.so.hints
/var/run/ld32.so.hints
    Conventional configuration files containing directory names for invocations with -32.

SEE ALSO
ld(1), link(5)

HISTORY
A ldconfig utility first appeared in SunOS 4.0, it appeared in its current form in FreeBSD 1.1.

BUGS
Some security checks (for example, verifying root ownership of added directories) are not performed when -aout is specified.