Ubuntu Manpage: ldconfig - configure dynamic linker run-time bindings

NAME

       ldconfig - configure dynamic linker run-time bindings

SYNOPSIS

       /sbin/ldconfig [-nNvXV] [-f conf] [-C cache] [-r root] directory...
       /sbin/ldconfig -l [-v] library...
       /sbin/ldconfig -p

DESCRIPTION

ldconfig creates the necessary links and cache to the most recent shared libraries found
in the directories specified on the command line, in the file /etc/ld.so.conf, and in the
trusted directories, /lib and /usr/lib (on some 64-bit architectures such as x86-64, /lib
and /usr/lib are the trusted directories for 32-bit libraries, while /lib64 and /usr/lib64
are used for 64-bit libraries).

The cache is used by the run-time linker, ld.so or ld-linux.so. ldconfig checks the
header and filenames of the libraries it encounters when determining which versions should
have their links updated.

ldconfig will attempt to deduce the type of ELF libraries (i.e., libc5 or libc6/glibc)
based on what C libraries, if any, the library was linked against.

Some existing libraries do not contain enough information to allow the deduction of their
type. Therefore, the /etc/ld.so.conf file format allows the specification of an expected
type. This is used only for those ELF libraries which we can not work out. The format is
"dirname=TYPE", where TYPE can be libc4, libc5, or libc6. (This syntax also works on the
command line.) Spaces are not allowed. Also see the -p option. ldconfig should normally
be run by the superuser as it may require write permission on some root owned directories
and files.

Note that ldconfig will only look at files that are named lib*.so* (for regular shared
objects) or ld-*.so* (for the dynamic loader itself). Other files will be ignored. Also,
ldconfig expects a certain pattern to how the symlinks are set up, like this example,
where the middle file (libfoo.so.1 here) is the SONAME for the library:

libfoo.so -> libfoo.so.1 -> libfoo.so.1.12

Failure to follow this pattern may result in compatibility issues after an upgrade.

OPTIONS

       -c fmt, --format=fmt
              (Since glibc 2.2) Cache format to use: old, new, or compat (default).

       -C cache
              Use cache instead of /etc/ld.so.cache.

       -f conf
              Use conf instead of /etc/ld.so.conf.

       -i, --ignore-aux-cache
              (Since glibc 2.7) Ignore auxiliary cache file.

       -l     (Since  glibc 2.2) Library mode.  Manually link individual libraries.  Intended for
              use by experts only.

       -n     Process only the directories specified on the  command  line.   Don't  process  the
              trusted directories, nor those specified in /etc/ld.so.conf.  Implies -N.

       -N     Don't rebuild the cache.  Unless -X is also specified, links are still updated.

       -p, --print-cache
              Print the lists of directories and candidate libraries stored in the current cache.

       -r root
              Change to and use root as the root directory.

       -v, --verbose
              Verbose  mode.   Print  current version number, the name of each directory as it is
              scanned, and any links that are created.  Overrides quiet mode.

       -V, --version
              Print program version.

       -X     Don't update links.  Unless -N is also specified, the cache is still rebuilt.

FILES

       /lib/ld.so
              Run-time linker/loader.
       /etc/ld.so.conf
              File containing a list of directories,  one  per  line,  in  which  to  search  for
              libraries.
       /etc/ld.so.cache
              File  containing an ordered list of libraries found in the directories specified in
              /etc/ld.so.conf, as well as those found in the trusted directories.

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