206 lines
6.0 KiB
Groff
206 lines
6.0 KiB
Groff
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.\" $OpenBSD: ld.so.1,v 1.25 2022/06/14 09:56:07 kn Exp $
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.\" $NetBSD: rtld.1,v 1.2 1995/10/08 23:43:28 pk 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 $Mdocdate: June 14 2022 $
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.Dt LD.SO 1
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.Os
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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's
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address space.
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It uses the data structures
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.Po
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see
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.Xr elf 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 successfully 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.
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A mechanism is provided for initialization routines to be called,
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on a per-object basis, giving a shared object an opportunity
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to perform any extra set-up, before execution of the program proper begins.
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.\"
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.\" <talk about CTORS/DTORS>
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.\"
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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 kernel.
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.\"
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.\" <How it is run>
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.\"
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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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.Aq library-name , major-version-number , minor-version-number .
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.Pp
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.Nm
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searches for shared objects in the following lists of paths:
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.Pp
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.Bl -enum -offset ident -compact
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.It
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.Ev LD_LIBRARY_PATH
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environment variable if set
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.It
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.Dv DT_RUNPATH
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of the calling object if set, otherwise:
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.Bl -enum -compact
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.It
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.Dv DT_RPATH
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of the calling object if set
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.It
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.Dv DT_RPATH
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of the program if set
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.El
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(The use of
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.Dv DT_RPATH
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is deprecated as its behaviour varies across operating systems.)
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.It
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default search path set by
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.Xr ldconfig 8
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.It
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.Pa /usr/lib
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.El
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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 Ds -compact
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.It Ev LD_LIBRARY_PATH
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A colon separated list of directories, prepending the default search path
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for shared libraries.
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This variable is ignored for set-user-ID and set-group-ID executables.
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.Pp
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.It Ev LD_PRELOAD
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A colon separated list of library names to load before any of the regular
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libraries are loaded.
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This variable is ignored for set-user-ID and set-group-ID executables.
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.Pp
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.It Ev LD_BIND_NOW
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Specifies that the dynamic linker should process all relocations before
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transferring control to the program.
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Normally, the procedure linkage table entries are handled lazily,
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avoiding symbol lookup and relocation for unused functions.
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This variable is ignored for set-user-ID and set-group-ID executables.
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.Pp
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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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.Pp
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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 Ns '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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.Ev LD_TRACE_LOADED_OBJECTS_FMT1
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is used for tracing shared libraries;
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.Ev LD_TRACE_LOADED_OBJECTS_FMT2
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for dynamically loaded objects, the dynamic linker,
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and the main executable.
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The following conversions can be used:
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.Bl -tag -width "xxxx"
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.It %a
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The main program's name
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.Pq also known as Dq __progname .
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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 %e
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The end address of the object.
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.It %g
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The object's group reference count.
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.It %m
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The object's major version number.
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.It %n
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The object's minor version number.
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.It \&%O
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The object's open count.
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.It %o
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The object name.
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.It %p
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The full pathname as determined by
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.Nm ld.so Ns 's
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library search rules.
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.It %r
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The object's reference count.
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.It %x
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The object'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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.Pp
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.It Ev LD_DEBUG
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When set, be verbose about what
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.Nm
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does.
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This variable is ignored for set-user-ID and set-group-ID executables.
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.El
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.Sh FILES
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.Bl -tag -width /var/run/ld.so.hintsXXX -compact
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.It Pa /var/run/ld.so.hints
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library location hints built by
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.Xr ldconfig 8
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.El
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.Sh SEE ALSO
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.Xr ld 1 ,
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.Xr elf 5 ,
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.Xr ldconfig 8
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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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