sbin/ldconfig/ldconfig.8

.\"
.\" Copyright (c) 1993 Paul Kranenburg
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.\" $FreeBSD: src/sbin/ldconfig/ldconfig.8,v 1.19.2.10 2003/05/13 19:25:19 trhodes Exp $
.\"
.Dd January 6, 2018
.Dt LDCONFIG 8
.Os
.Sh NAME
.Nm ldconfig
.Nd configure the shared library cache
.Sh SYNOPSIS
.Nm
.Op Fl elf
.Op Fl Rimr
.Op Fl f Ar hints_file
.Op Ar directory | Ar
.Sh DESCRIPTION
The
.Nm
utility is used to prepare a set of
.Dq 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
.Ar 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.
.Pp
Alternatively,
.Ar files
may be specified; these 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
.Ql \&#
are ignored.
Filenames must conform to the
.Pa lib*.so.[0-9]
pattern in order to be added to the hints file.
.Pp
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
.Fl i
option is present.
.Pp
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.
.Pp
The
.Ev 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.
.Ev LD_LIBRARY_PATH
is a
.Sq \&:
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
.Fl L
switch of
.Xr ld 1 .
.Pp
The
.Nm
utility is typically run as part of the boot sequence.
.Pp
The following options are recognized by
.Nm :
.Bl -tag -width indent
.It Fl elf
Generate the hints for ELF format shared libraries.
.It Fl 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.
.It Fl f Ar hints_file
Read and/or update the specified hints file, instead of the standard file.
This option is provided primarily for testing.
.It Fl i
Run in insecure mode.
The security checks will not be performed.
.It Fl m
Instead of replacing the contents of the hints file
with those found in the directories specified,
.Dq merge
in new entries.
Directories recorded in the hints file by previous runs of
.Nm
are also rescanned for new shared libraries.
.It Fl 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.
.It Fl s
Ignored for compatibility with other operating systems.
.El
.Sh SECURITY
Special care must be taken when loading shared libraries into the address
space of
.Ev 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
.Ev LD_LIBRARY_PATH
is not used to search for libraries.
Thus, the role of
.Nm
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.
.Sh FILES
.Bl -tag -width /var/run/ld-elf.so.hintsxxx -compact
.It Pa /var/run/ld-elf.so.hints
Standard hints file for the ELF dynamic linker.
.It Pa /etc/ld-elf.so.conf
Conventional configuration file containing directory names for
invocations with
.Fl elf .
.El
.Sh SEE ALSO
.Xr ld 1 ,
.Xr link 5
.Sh HISTORY
A
.Nm
utility first appeared in SunOS 4.0, it appeared in its current form
in
.Fx 1.1 .