freebsd/sbin/ldconfig/ldconfig.8

.\"
.\" Copyright (c) 1993 Paul Kranenburg
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.\" $FreeBSD$
.\"
.Dd October 3, 1993
.Dt LDCONFIG 8
.Os FreeBSD
.Sh NAME
.Nm ldconfig
.Nd configure the shared library cache
.Sh SYNOPSIS
.Nm ldconfig
.Op Fl aout | Fl elf
.Op Fl Rmrsv
.Op Fl f Ar hints_file
.Op Ar directory | file Ar ...
.Sh DESCRIPTION
.Nm
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
Files named on the command line 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.
.Pp
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.
.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
.Nm Ldconfig
is typically run as part of the boot sequence.
.Pp
The following options recognized by
.Nm ldconfig:
.Bl -tag -width indent
.It Fl aout
Generate the hints for a.out format shared libraries.
.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.
.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 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
Do not scan the built-in system directory
.Pq Dq /usr/lib
for shared libraries.
.It Fl v
Switch on verbose mode.
.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,
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 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
.Nm ldconfig
are under control of the system's administrator.
.Sh ENVIRONMENT
.Bl -tag -width OBJFORMATxxx -compact
.It Ev OBJFORMAT
Overrides
.Pa /etc/objformat
(see below) to determine whether
.Fl aout
or
.Fl elf
is the default.  If set, its value should be either
.Ql aout
or
.Ql elf .
.El
.Sh FILES
.Bl -tag -width /var/run/ld-elf.so.hintsxxx -compact
.It Pa /var/run/ld.so.hints
Standard hints file for the a.out dynamic linker.
.It Pa /var/run/ld-elf.so.hints
Standard hints file for the ELF dynamic linker.
.It Pa /etc/ld.so.conf
Conventional configuration file containing directory names for
invocations with
.Fl aout .
.It Pa /etc/ld-elf.so.conf
Conventional configuration file containing directory names for
invocations with
.Fl elf .
.It Pa /etc/objformat
Determines whether
.Fl aout
or
.Fl elf
is the default.  If present, it must consist of a single line
containing either
.Ql OBJFORMAT=aout
or
.Ql OBJFORMAT=elf .
.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 FreeBSD 1.1.