LD.SO(8) Linux Programmer's Manual LD.SO(8)
NAME
ld.so, ld-linux.so* - dynamic linker/loader
DESCRIPTION
The programs ld.so and ld-linux.so* find and load the shared libraries
needed by a program, prepare the program to run, and then run it.
Linux binaries require dynamic linking (linking at run time) unless the
-static option was given to ld during compilation.
The program ld.so handles a.out binaries, a format used long ago; ld-
linux.so* handles ELF (/lib/ld-linux.so.1 for libc5, /lib/ld-linux.so.2
for glibc2), which everybody has been using for years now. Otherwise
both have the same behaviour, and use the same support files and pro-
grams ldd(1), ldconfig(8) and /etc/ld.so.conf.
The shared libraries needed by the program are searched for in various
places:
o (ELF only) Using the DT_RPATH dynamic section attribute of the
binary if present and DT_RUNPATH attribute does not exist. Use
of DT_RPATH is deprecated.
o Using the environment variable LD_LIBRARY_PATH. Except if the
executable is a set-user-ID/set-group-ID binary, in which case
it is ignored.
o (ELF only) Using the DT_RUNPATH dynamic section attribute of the
binary if present.
o From the cache file /etc/ld.so.cache which contains a compiled
list of candidate libraries previously found in the augmented
library path. If, however, the binary was linked with -z node-
flib linker option, libraries in the default library paths are
skipped.
o In the default path /lib, and then /usr/lib. If the binary was
linked with -z nodeflib linker option, this step is skipped.
SYNOPSIS
The dynamic linker can be run either indirectly through running some
dynamically linked program or library (in which case no command line
options to the dynamic linker can be passed and, in the ELF case, the
dynamic linker which is stored in the .interp section of the program is
executed) or directly by running:
/lib/ld-linux.so.* [OPTIONS] [PROGRAM [ARGUMENTS]]
COMMAND LINE OPTIONS
--list List all dependencies and how they are resolved.
--verify
Verify that program is dynamically linked and this dynamic
linker can handle it.
--library-path PATH
Override LD_LIBRARY_PATH environment variable setting (see
below).
--ignore-rpath LIST
Ignore RPATH and RUNPATH information in object names in LIST.
This option has been supported by glibc2 for about one hour.
Then it was renamed into:
--inhibit-rpath LIST
ENVIRONMENT
There are four important environment variables.
LD_LIBRARY_PATH
A colon-separated list of directories in which to search for ELF
libraries at execution-time. Similar to the PATH environment
variable.
LD_PRELOAD
A whitespace-separated list of additional, user-specified, ELF
shared libraries to be loaded before all others. This can be
used to selectively override functions in other shared
libraries. For set-user-ID/set-group-ID ELF binaries, only
libraries in the standard search directories that are also set-
user-ID will be loaded.
LD_BIND_NOW
(libc5; glibc since 2.1.1) If set to non-empty string, causes
the dynamic linker to resolve all symbols at program startup
instead of deferring function call resolval to the point when
they are first referenced. This is useful when using a debug-
ger.
LD_TRACE_LOADED_OBJECTS
(ELF only) If set to non-empty string, causes the program to
list its dynamic library dependencies, as if run by ldd(1),
instead of running normally.
Then there are lots of more or less obscure variables, many obsolete or
only for internal use.
LD_WARN
(ELF only)(glibc since 2.1.3) If set to non-empty string, warn
about unresolved symbols.
LD_NOWARN
(a.out only)(libc5) Suppress warnings about a.out libraries with
incompatible minor version numbers.
LD_BIND_NOT
(glibc since 2.1.95) Do not update the GOT (global offset table)
and PLT (procedure linkage table) after resolving a symbol.
LD_DEBUG
(glibc since 2.1) Output verbose debugging information about the
dynamic linker. If set to all prints all debugging information
it has, if set to help prints a help message about which cate-
gories can be specified in this environment variable.
LD_DEBUG_OUTPUT
(glibc since 2.1) File where LD_DEBUG output should be fed into,
default is standard output. LD_DEBUG_OUTPUT is ignored for set-
user-ID/set-group-ID binaries.
LD_VERBOSE
(glibc since 2.1) If set to non-empty string, output symbol ver-
sioning information about the program if querying information
about the program (ie. either LD_TRACE_LOADED_OBJECTS has been
set, or --list or --verify options have been given to the
dynamic linker).
LD_PROFILE
(glibc since 2.1) Shared object to be profiled.
LD_PROFILE_OUTPUT
(glibc since 2.1) File where LD_PROFILE output should be stored,
default is standard output. LD_PROFILE_OUTPUT is ignored for
set-user-ID/set-group-ID binaries.
LD_AOUT_LIBRARY_PATH
(libc5) Version of LD_LIBRARY_PATH for a.out binaries only. Old
versions of ld-linux.so.1 also supported LD_ELF_LIBRARY_PATH.
LD_AOUT_PRELOAD
(libc5) Version of LD_PRELOAD for a.out binaries only. Old ver-
sions of ld-linux.so.1 also supported LD_ELF_PRELOAD.
LD_SHOW_AUXV
(glibc since 2.1) Show auxiliary array passed up from the ker-
nel.
LD_HWCAP_MASK
(glibc since 2.1) Mask for hardware capabilities.
LD_ORIGIN_PATH
(glibc since 2.1) Path where the binary is found (for non-set-
user-ID programs).
LD_DYNAMIC_WEAK
(glibc since 2.1.91) Allow weak symbols to be overridden
(reverting to old glibc behaviour).
LD_KEEPDIR
(a.out only)(libc5) Don't ignore the directory in the names of
a.out libraries to be loaded. Use of this option is strongly
discouraged.
LDD_ARGV0
(libc5) argv[0] to be used by ldd(1) when none is present.
FILES
/lib/ld.so
a.out dynamic linker/loader
/lib/ld-linux.so.{1,2}
ELF dynamic linker/loader
/etc/ld.so.cache
File containing a compiled list of directories in which to
search for libraries and an ordered list of candidate libraries.
/etc/ld.so.preload
File containing a whitespace separated list of ELF shared
libraries to be loaded before the program.
lib*.so*
shared libraries
NOTES
The ld.so functionality is available for executables compiled using
libc version 4.4.3 or greater. ELF functionality is available since
Linux 1.1.52 and libc5.
SEE ALSO
ldd(1), ldconfig(8)
2001-12-16 LD.SO(8)