sbin/ldconfig/ldconfig.8

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.Dd May 15, 2021
.Dt LDCONFIG 8
.Os
.Sh NAME
.Nm ldconfig
.Nd configure the dynamic linker search path for shared libraries
.Sh SYNOPSIS
.Nm
.Op Fl 32
.Op Fl Rimrsv
.Op Fl f Ar hints_file
.Op Ar directory | Ar
.Sh DESCRIPTION
.Nm
utility is used to configure the set of paths used by the dynamic linker
.Xr ld-elf.so.1 1
when searching for shared libraries.
The dynamic linker looks for libraries in a set of built-in system directories
and any directories specified in the hints file.
This obviates the need for storing search paths within the executable,
see the
.Fl rpath
option for the static linker
.Xr ld 1 .
.Pp
The hints file is maintained by
.Nm .
The
.Ar directories
list to be stored in the hints file is supplied on the command line.
.Pp
Alternatively to the
.Ar directories
list on the command line,
.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.
.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
.Ev LD_LIBRARY_PATH
environment variable can be used to specify additional
shared library search directories.
.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 following options are recognized by
.Nm :
.Bl -tag -width indent
.It Fl 32
Generate the hints for 32-bit ABI shared libraries
on 64-bit systems that support running 32-bit binaries.
.It Fl elf
Ignored for backwards compatibility.
.It Fl R
Appends pathnames on the command line to the directory list from
the hints file.
.Pp
This is the default action when no options 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 list of the directories to search with the
directories specified on the command line, merge existing list
with the specified directories, and write the result to the hints file.
.It Fl r
List the current list of the directories from the hints file
on the standard output.
The hints file is not modified.
.Pp
Scan and print all libraries found on the directories list.
.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.
.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 paths found in
the hints file.
In particular, the
.Ev LD_LIBRARY_PATH
is not used to search for libraries.
Thus,
.Nm
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 .
.It Pa /var/run/ld-elf32.so.hints
Conventional configuration files containing directory names for
invocations with
.Fl 32 .
.El
.Sh SEE ALSO
.Xr ld 1 ,
.Xr ld-elf.so.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 .
.Pp
The name 'hints file' is historic from the times when the file also contained
hints to the dynamic linker.
This functionality is not provided for ELF.