MirOS Manual: ldconfig(8)

LDCONFIG(8)              BSD System Manager's Manual               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 per-
     form 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 addi-
     tional 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 argu-
             ments 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 el-
             iminate 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 li-
     braries and programs using -P, program startup can be significantly im-
     proved 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), link(5), rc.conf(8)

HISTORY

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

MirOS BSD #10-current          October 3, 1993                               1

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