5584286a91
configurable fallback search paths, as well as new crt interface version. Also: - even faster getenv(), get all environment variable settings in a single pass. - ldd printf-like format specifications - minor code cleanups, one vsprintf -> vsnprintf (harmless) The library search sequence is a little more complete now. Before, it'd search $LD_LIBRARY_PATH (by opendir/readdir/closedir), then read the hints file, then read /usr/lib (again by scanning thr directory). It would then fail if there was no "found" library. Now, it does LD_LIBRARY_PATH and the hints file the same, but then uses a longer fallback path. The -R path is fetched from the executable if specified at build time, the ldconfig path is appended, and /usr/lib is appended to that. Duplicates are suppressed. This means that simply placing a new library in /usr/local/lib will work (the same as it did in /usr/lib) without needing ldconfig -m. It will find it quicker if the ldconfig is run though. Similar changes have been made to the NetBSD ld.so, but ours is rather different now due to John Polstra's speedups and fixes from a while back. The ldd printf-like format support came direct from NetBSD. Reviewed by: nate, jdp
191 lines
6.2 KiB
Groff
191 lines
6.2 KiB
Groff
.\" $Id: rtld.1,v 1.4 1996/09/23 22:22:03 wosch Exp $
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.\"
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.\" Copyright (c) 1995 Paul Kranenburg
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed by Paul Kranenburg.
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.\" 3. The name of the author may not be used to endorse or promote products
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.\" derived from this software without specific prior written permission
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
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.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
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.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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.\"
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.Dd June 27, 1995
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.Dt RTLD 1
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.Os FreeBSD
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.Sh NAME
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.Nm ld.so
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.Nd run-time link-editor
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.Sh DESCRIPTION
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.Nm
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is a self-contained, position independent program image providing run-time
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support for loading and link-editing shared objects into a process'
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address space. It uses the data structures
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.Po
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see
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.Xr link 5
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.Pc
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contained within dynamically linked programs to determine which shared
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libraries are needed and loads them at a convenient virtual address
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using the
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.Xr mmap 2
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system call.
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.Pp
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After all shared libraries have been succesfully loaded,
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.Nm
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proceeds to resolve external references from both the main program and
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all objects loaded. A mechanism is provided for initialisation routines
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to be called, on a per-object basis, giving a shared object an opportunity
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to perfrom any extra set-up, before execution of the program proper begins.
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This is useful for C++ libraries that contain static constrictors.
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.Pp
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.Nm
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is itself a shared object that is initially loaded by the startup module
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.Em crt0 .
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Since
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.Xr a.out 5
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formats do not provide easy access to the file header from within a running
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process,
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.Em crt0
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uses the special symbol
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.Va _DYNAMIC
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to determine whether a program is in fact dynamically linked or not. Whenever
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the linker
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.Xr ld 1
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has relocated this symbol to a location other then 0,
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.Em crt0
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assumes the services of
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.Nm
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are needed
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.Po
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see
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.Xr link 5
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for details
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.Pc \&.
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.Em crt0
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passes control to
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.Nm
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\&'s entry point before the program's
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.Fn main
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routine is called. Thus,
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.Nm
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can complete the link-editing process before the dynamic program calls upon
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services of any dynamic library.
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.Pp
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To quickly locate the required shared objects in the filesystem,
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.Nm
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may use a
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.Dq hints
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file, prepared by the
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.Xr ldconfig 8
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utility, in which the full path specification of the shared objects can be
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looked up by hashing on the 3-tuple
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.Ao
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library-name, major-version-number, minor-version-number
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.Ac \&.
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.Pp
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.Nm
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recognises a number of environment variables that can be used to modify
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its behaviour as follows:
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.Pp
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.Bl -tag -width "LD_TRACE_LOADED_OBJECTS_PROGNAME"
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.It Ev LD_LIBRARY_PATH
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A colon separated list of directories, overriding the default search path
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for shared libraries.
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This is ignored for set-user-ID and set-group-ID programs.
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.It Ev LD_PRELOAD
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A colon separated list of shared libraries, to be linked in before any
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other shared libraries. If the directory is not specified then
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the directories specified by LD_LIBRARY_PATH will be searched first
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followed by the set of built-in standard directories.
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This is ignored for set-user-ID and set-group-ID programs.
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.It Ev LD_WARN_NON_PURE_CODE
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When set, issue a warning whenever a link-editing operation requires
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modification of the text segment of some loaded object. This is usually
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indicative of an incorrectly built library.
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.It Ev LD_SUPPRESS_WARNINGS
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When set, no warning messages of any kind are issued. Normally, a warning
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is given if satisfactorily versioned library could not be found.
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.It Ev LD_TRACE_LOADED_OBJECTS
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When set, causes
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.Nm
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to exit after loading the shared objects and printing a summary which includes
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the absolute pathnames of all objects, to standard output.
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.It Ev LD_TRACE_LOADED_OBJECTS_FMT1
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.It Ev LD_TRACE_LOADED_OBJECTS_FMT2
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When set, these variables are interpreted as format strings a la
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.Xr printf 3
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to customize the trace output and are used by
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.Xr ldd 1 's
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.Fl f
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option and allows
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.Xr ldd 1
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to be operated as a filter more conveniently.
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The following conversions can be used:
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.Bl -tag -indent "LD_TRACE_LOADED_OBJECTS_FMT1 " -width "xxxx"
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.It \&%a
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The main program's name
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.Po also known as
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.Dq __progname
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.Pc .
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.It \&%A
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The value of the environment variable
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.Ev LD_TRACE_LOADED_OBJECTS_PROGNAME
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.It \&%o
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The libary name.
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.It \&%m
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The library's major version numer.
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.It \&%n
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The library's minor version numer.
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.It \&%p
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The full pathname as determined by
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.Nm rtld Ns 's
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library search rules.
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.It \&%x
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The library's load address.
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.El
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.Pp
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Additionally,
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.Sy \en
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and
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.Sy \et
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are recognised and have their usual meaning.
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.\" .It Ev LD_NO_INTERN_SEARCH
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.\" When set,
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.\" .Nm
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.\" does not process any internal search paths that were recorded in the
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.\" executable.
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.\" .It Ev LD_NOSTD_PATH
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.\" When set, do not include a set of built-in standard directory paths for
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.\" searching. This might be useful when running on a system with a completely
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.\" non-standard filesystem layout.
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.El
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.Pp
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.Sh FILES
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/var/run/ld.so.hints
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.Pp
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.Sh SEE ALSO
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.Xr ld 1 ,
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.Xr ldconfig 8 ,
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.Xr link 5
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.Sh HISTORY
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The shared library model employed first appeared in SunOS 4.0
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