Manual: ld.so
ld.so(8) System Manager's Manual ld.so(8)
NAME
ld.so, ld-linux.so - dynamic linker/loader
SYNOPSIS
The dynamic linker can be run either indirectly by running some dynamically linked program or shared object (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]]
DESCRIPTION
The programs ld.so and ld-linux.so* find and load the shared objects (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(1) during comâ
pilation.
The program ld.so handles a.out binaries, a binary format used long ago. The program ld-linux.so*
(/lib/ld-linux.so.1 for libc5, /lib/ld-linux.so.2 for glibc2) handles binaries that are in the more modern ELF forâ
mat. Both programs have the same behavior, and use the same support files and programs (ldd(1), ldconfig(8), and
/etc/ld.so.conf).
When resolving shared object dependencies, the dynamic linker first inspects each dependency string to see if it conâ
tains a slash (this can occur if a shared object pathname containing slashes was specified at link time). If a slash
is found, then the dependency string is interpreted as a (relative or absolute) pathname, and the shared object is
loaded using that pathname.
If a shared object dependency does not contain a slash, then it is searched for in the following order:
(1) Using the directories specified in the DT_RPATH dynamic section attribute of the binary if present and DT_RUNâ
PATH attribute does not exist.
(2) Using the environment variable LD_LIBRARY_PATH, unless the executable is being run in secure-execution mode (see
below), in which case this variable is ignored.
(3) Using the directories specified in the DT_RUNPATH dynamic section attribute of the binary if present. Such diâ
rectories are searched only to find those objects required by DT_NEEDED (direct dependencies) entries and do not
apply to those objects' children, which must themselves have their own DT_RUNPATH entries. This is unlike
DT_RPATH, which is applied to searches for all children in the dependency tree.
(4) From the cache file /etc/ld.so.cache, which contains a compiled list of candidate shared objects previously
found in the augmented library path. If, however, the binary was linked with the -z nodefaultlib linker option,
shared objects in the default paths are skipped. Shared objects installed in hardware capability directories
(see below) are preferred to other shared objects.
(5) In the default path /lib, and then /usr/lib. (On some 64-bit architectures, the default paths for 64-bit shared
objects are /lib64, and then /usr/lib64.) If the binary was linked with the -z nodefaultlib linker option, this
step is skipped.
Dynamic string tokens
In several places, the dynamic linker expands dynamic string tokens:
⢠In the environment variables LD_LIBRARY_PATH, LD_PRELOAD, and LD_AUDIT,
⢠inside the values of the dynamic section tags DT_NEEDED, DT_RPATH, DT_RUNPATH, DT_AUDIT, and DT_DEPAUDIT of ELF
binaries,
⢠in the arguments to the ld.so command line options --audit, --library-path, and --preload (see below), and
⢠in the filename arguments to the dlopen(3) and dlmopen(3) functions.
The substituted tokens are as follows:
$ORIGIN (or equivalently ${ORIGIN})
This expands to the directory containing the program or shared object. Thus, an application located in
somedir/app could be compiled with
gcc -Wl,-rpath,'$ORIGIN/../lib'
so that it finds an associated shared object in somedir/lib no matter where somedir is located in the direcâ
tory hierarchy. This facilitates the creation of "turn-key" applications that do not need to be installed
into special directories, but can instead be unpacked into any directory and still find their own shared obâ
jects.
$LIB (or equivalently ${LIB})
This expands to lib or lib64 depending on the architecture (e.g., on x86-64, it expands to lib64 and on
x86-32, it expands to lib).
$PLATFORM (or equivalently ${PLATFORM})
This expands to a string corresponding to the processor type of the host system (e.g., "x86_64"). On some arâ
chitectures, the Linux kernel doesn't provide a platform string to the dynamic linker. The value of this
string is taken from the AT_PLATFORM value in the auxiliary vector (see getauxval(3)).
Note that the dynamic string tokens have to be quoted properly when set from a shell, to prevent their expansion as
shell or environment variables.
OPTIONS
--argv0 string (since glibc 2.33)
Set argv[0] to the value string before running the program.
--audit list
Use objects named in list as auditors. The objects in list are delimited by colons.
--glibc-hwcaps-mask list
only search built-in subdirectories if in list.
--glibc-hwcaps-prepend list
Search glibc-hwcaps subdirectories in list.
--inhibit-cache
Do not use /etc/ld.so.cache.
--library-path path
Use path instead of LD_LIBRARY_PATH environment variable setting (see below). The names ORIGIN, LIB, and
PLATFORM are interpreted as for the LD_LIBRARY_PATH environment variable.
--inhibit-rpath list
Ignore RPATH and RUNPATH information in object names in list. This option is ignored when running in secure-
execution mode (see below). The objects in list are delimited by colons or spaces.
--list List all dependencies and how they are resolved.
--list-diagnostics (since glibc 2.33)
Print system diagnostic information in a machine-readable format, such as some internal loader variables, the
auxiliary vector (see getauxval(3)), and the environment variables. On some architectures, the command might
print additional information (like the cpu features used in GNU indirect function selection on x86).
--list-tunables (since glibc 2.33) Print the names and values of all tunables, along with the minimum and maxâ
imum allowed values.
--preload list (since glibc 2.30)
Preload the objects specified in list. The objects in list are delimited by colons or spaces. The objects
are preloaded as explained in the description of the LD_PRELOAD environment variable below.
By contrast with LD_PRELOAD, the --preload option provides a way to perform preloading for a single executable
without affecting preloading performed in any child process that executes a new program.
--verify
Verify that program is dynamically linked and this dynamic linker can handle it.
ENVIRONMENT
Various environment variables influence the operation of the dynamic linker.
Secure-execution mode
For security reasons, if the dynamic linker determines that a binary should be run in secure-execution mode, the efâ
fects of some environment variables are voided or modified, and furthermore those environment variables are stripped
from the environment, so that the program does not even see the definitions. Some of these environment variables afâ
fect the operation of the dynamic linker itself, and are described below. Other environment variables treated in
this way include: GCONV_PATH, GETCONF_DIR, HOSTALIASES, LOCALDOMAIN, LD_AUDIT, LD_DEBUG, LD_DEBUG_OUTPUT, LD_DYâ
NAMIC_WEAK, LD_HWCAP_MASK, LD_LIBRARY_PATH, LD_ORIGIN_PATH, LD_PRELOAD, LD_PROFILE, LD_SHOW_AUXV, LOCALDOMAIN, LOCâ
PATH, MALLOC_TRACE, NIS_PATH, NLSPATH, RESOLV_HOST_CONF, RES_OPTIONS, TMPDIR, and TZDIR.
A binary is executed in secure-execution mode if the AT_SECURE entry in the auxiliary vector (see getauxval(3)) has a
nonzero value. This entry may have a nonzero value for various reasons, including:
⢠The process's real and effective user IDs differ, or the real and effective group IDs differ. This typically ocâ
curs as a result of executing a set-user-ID or set-group-ID program.
⢠A process with a non-root user ID executed a binary that conferred capabilities to the process.
⢠A nonzero value may have been set by a Linux Security Module.
Environment variables
Among the more important environment variables are the following:
LD_ASSUME_KERNEL (from glibc 2.2.3 to glibc 2.36)
Each shared object can inform the dynamic linker of the minimum kernel ABI version that it requires. (This
requirement is encoded in an ELF note section that is viewable via readelf -n as a section labeled
NT_GNU_ABI_TAG.) At run time, the dynamic linker determines the ABI version of the running kernel and will
reject loading shared objects that specify minimum ABI versions that exceed that ABI version.
LD_ASSUME_KERNEL can be used to cause the dynamic linker to assume that it is running on a system with a difâ
ferent kernel ABI version. For example, the following command line causes the dynamic linker to assume it is
running on Linux 2.2.5 when loading the shared objects required by myprog:
$ LD_ASSUME_KERNEL=2.2.5 ./myprog
On systems that provide multiple versions of a shared object (in different directories in the search path)
that have different minimum kernel ABI version requirements, LD_ASSUME_KERNEL can be used to select the verâ
sion of the object that is used (dependent on the directory search order).
Historically, the most common use of the LD_ASSUME_KERNEL feature was to manually select the older Linuxâ
Threads POSIX threads implementation on systems that provided both LinuxThreads and NPTL (which latter was
typically the default on such systems); see pthreads(7).
LD_BIND_NOW (since glibc 2.1.1)
If set to a nonempty string, causes the dynamic linker to resolve all symbols at program startup instead of
deferring function call resolution to the point when they are first referenced. This is useful when using a
debugger.
LD_LIBRARY_PATH
A list of directories in which to search for ELF libraries at execution time. The items in the list are sepaâ
rated by either colons or semicolons, and there is no support for escaping either separator. A zero-length
directory name indicates the current working directory.
This variable is ignored in secure-execution mode.
Within the pathnames specified in LD_LIBRARY_PATH, the dynamic linker expands the tokens $ORIGIN, $LIB, and
$PLATFORM (or the versions using curly braces around the names) as described above in Dynamic string tokens.
Thus, for example, the following would cause a library to be searched for in either the lib or lib64 subdirecâ
tory below the directory containing the program to be executed:
$ LD_LIBRARY_PATH='$ORIGIN/$LIB' prog
(Note the use of single quotes, which prevent expansion of $ORIGIN and $LIB as shell variables!)
LD_PRELOAD
A list of additional, user-specified, ELF shared objects to be loaded before all others. This feature can be
used to selectively override functions in other shared objects.
The items of the list can be separated by spaces or colons, and there is no support for escaping either sepaâ
rator. The objects are searched for using the rules given under DESCRIPTION. Objects are searched for and
added to the link map in the left-to-right order specified in the list.
In secure-execution mode, preload pathnames containing slashes are ignored. Furthermore, shared objects are
preloaded only from the standard search directories and only if they have set-user-ID mode bit enabled (which
is not typical).
Within the names specified in the LD_PRELOAD list, the dynamic linker understands the tokens $ORIGIN, $LIB,
and $PLATFORM (or the versions using curly braces around the names) as described above in Dynamic string toâ
kens. (See also the discussion of quoting under the description of LD_LIBRARY_PATH.)
There are various methods of specifying libraries to be preloaded, and these are handled in the following orâ
der:
(1) The LD_PRELOAD environment variable.
(2) The --preload command-line option when invoking the dynamic linker directly.
(3) The /etc/ld.so.preload file (described below).
LD_TRACE_LOADED_OBJECTS
If set (to any value), causes the program to list its dynamic 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_AUDIT (since glibc 2.4)
A list of user-specified, ELF shared objects to be loaded before all others in a separate linker namespace
(i.e., one that does not intrude upon the normal symbol bindings that would occur in the process) These obâ
jects can be used to audit the operation of the dynamic linker. The items in the list are colon-separated,
and there is no support for escaping the separator.
LD_AUDIT is ignored in secure-execution mode.
The dynamic linker will notify the audit shared objects at so-called auditing checkpointsâfor example, loading
a new shared object, resolving a symbol, or calling a symbol from another shared objectâby calling an approâ
priate function within the audit shared object. For details, see rtld-audit(7). The auditing interface is
largely compatible with that provided on Solaris, as described in its Linker and Libraries Guide, in the chapâ
ter Runtime Linker Auditing Interface.
Within the names specified in the LD_AUDIT list, the dynamic linker understands the tokens $ORIGIN, $LIB, and
$PLATFORM (or the versions using curly braces around the names) as described above in Dynamic string tokens.
(See also the discussion of quoting under the description of LD_LIBRARY_PATH.)
Since glibc 2.13, in secure-execution mode, names in the audit list that contain slashes are ignored, and only
shared objects in the standard search directories that have the set-user-ID mode bit enabled are loaded.
LD_BIND_NOT (since glibc 2.1.95)
If this environment variable is set to a nonempty string, do not update the GOT (global offset table) and PLT
(procedure linkage table) after resolving a function symbol. By combining the use of this variable with
LD_DEBUG (with the categories bindings and symbols), one can observe all run-time function bindings.
LD_DEBUG (since glibc 2.1)
Output verbose debugging information about operation of the dynamic linker. The content of this variable is
one or more of the following categories, separated by colons, commas, or (if the value is quoted) spaces:
help Specifying help in the value of this variable does not run the specified program, and displays a
help message about which categories can be specified in this environment variable.
all Print all debugging information (except statistics and unused; see below).
bindings Display information about which definition each symbol is bound to.
files Display progress for input file.
libs Display library search paths.
reloc Display relocation processing.
scopes Display scope information.
statistics Display relocation statistics.
symbols Display search paths for each symbol look-up.
unused Determine unused DSOs.
versions Display version dependencies.
Since glibc 2.3.4, LD_DEBUG is ignored in secure-execution mode, unless the file /etc/suid-debug exists (the
content of the file is irrelevant).
LD_DEBUG_OUTPUT (since glibc 2.1)
By default, LD_DEBUG output is written to standard error. If LD_DEBUG_OUTPUT is defined, then output is writâ
ten to the pathname specified by its value, with the suffix "." (dot) followed by the process ID appended to
the pathname.
LD_DEBUG_OUTPUT is ignored in secure-execution mode.
LD_DYNAMIC_WEAK (since glibc 2.1.91)
By default, when searching shared libraries to resolve a symbol reference, the dynamic linker will resolve to
the first definition it finds.
Old glibc versions (before glibc 2.2), provided a different behavior: if the linker found a symbol that was
weak, it would remember that symbol and keep searching in the remaining shared libraries. If it subsequently
found a strong definition of the same symbol, then it would instead use that definition. (If no further symâ
bol was found, then the dynamic linker would use the weak symbol that it initially found.)
The old glibc behavior was nonstandard. (Standard practice is that the distinction between weak and strong
symbols should have effect only at static link time.) In glibc 2.2, the dynamic linker was modified to proâ
vide the current behavior (which was the behavior that was provided by most other implementations at that
time).
Defining the LD_DYNAMIC_WEAK environment variable (with any value) provides the old (nonstandard) glibc behavâ
ior, whereby a weak symbol in one shared library may be overridden by a strong symbol subsequently discovered
in another shared library. (Note that even when this variable is set, a strong symbol in a shared library
will not override a weak definition of the same symbol in the main program.)
Since glibc 2.3.4, LD_DYNAMIC_WEAK is ignored in secure-execution mode.
LD_HWCAP_MASK (from glibc 2.1 to glibc 2.38)
Mask for hardware capabilities. Since glibc 2.26, the option might be ignored if glibc does not support tunâ
ables.
LD_ORIGIN_PATH (since glibc 2.1)
Path where the binary is found.
Since glibc 2.4, LD_ORIGIN_PATH is ignored in secure-execution mode.
LD_POINTER_GUARD (from glibc 2.4 to glibc 2.22)
Set to 0 to disable pointer guarding. Any other value enables pointer guarding, which is also the default.
Pointer guarding is a security mechanism whereby some pointers to code stored in writable program memory (reâ
turn addresses saved by setjmp(3) or function pointers used by various glibc internals) are mangled semi-ranâ
domly to make it more difficult for an attacker to hijack the pointers for use in the event of a buffer overâ
run or stack-smashing attack. Since glibc 2.23, LD_POINTER_GUARD can no longer be used to disable pointer
guarding, which is now always enabled.
LD_PROFILE (since glibc 2.1)
The name of a (single) shared object to be profiled, specified either as a pathname or a soname. Profiling
output is appended to the file whose name is: $LD_PROFILE_OUTPUT/$LD_PROFILE.profile.
Since glibc 2.2.5, LD_PROFILE uses a different default path in secure-execution mode.
LD_PROFILE_OUTPUT (since glibc 2.1)
Directory where LD_PROFILE output should be written. If this variable is not defined, or is defined as an
empty string, then the default is /var/tmp.
LD_PROFILE_OUTPUT is ignored in secure-execution mode; instead /var/profile is always used.
LD_SHOW_AUXV (since glibc 2.1)
If this environment variable is defined (with any value), show the auxiliary array passed up from the kernel
(see also getauxval(3)).
Since glibc 2.3.4, LD_SHOW_AUXV is ignored in secure-execution mode.
LD_TRACE_PRELINKING (from glibc 2.4 to glibc 2.35)
If this environment variable is defined, trace prelinking of the object whose name is assigned to this enviâ
ronment variable. (Use ldd(1) to get a list of the objects that might be traced.) If the object name is not
recognized, then all prelinking activity is traced.
LD_USE_LOAD_BIAS (from glibc 2.3.3 to glibc 2.35)
By default (i.e., if this variable is not defined), executables and prelinked shared objects will honor base
addresses of their dependent shared objects and (nonprelinked) position-independent executables (PIEs) and
other shared objects will not honor them. If LD_USE_LOAD_BIAS is defined with the value 1, both executables
and PIEs will honor the base addresses. If LD_USE_LOAD_BIAS is defined with the value 0, neither executables
nor PIEs will honor the base addresses.
Since glibc 2.3.3, this variable is ignored in secure-execution mode.
LD_VERBOSE (since glibc 2.1)
If set to a nonempty string, output symbol versioning information about the program if the LD_TRACE_LOADED_OBâ
JECTS environment variable has been set.
LD_WARN (since glibc 2.1.3)
If set to a nonempty string, warn about unresolved symbols.
LD_PREFER_MAP_32BIT_EXEC (x86-64 only; since glibc 2.23)
According to the Intel Silvermont software optimization guide, for 64-bit applications, branch prediction perâ
formance can be negatively impacted when the target of a branch is more than 4 GB away from the branch. If
this environment variable is set (to any value), the dynamic linker will first try to map executable pages usâ
ing the mmap(2) MAP_32BIT flag, and fall back to mapping without that flag if that attempt fails. NB:
MAP_32BIT will map to the low 2 GB (not 4 GB) of the address space.
Because MAP_32BIT reduces the address range available for address space layout randomization (ASLR), LD_PREâ
FER_MAP_32BIT_EXEC is always disabled in secure-execution mode.
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 shared objects and an ordered list of
candidate shared objects. See ldconfig(8).
/etc/ld.so.preload
File containing a whitespace-separated list of ELF shared objects to be loaded before the program. See the
discussion of LD_PRELOAD above. If both LD_PRELOAD and /etc/ld.so.preload are employed, the libraries speciâ
fied by LD_PRELOAD are preloaded first. /etc/ld.so.preload has a system-wide effect, causing the specified
libraries to be preloaded for all programs that are executed on the system. (This is usually undesirable, and
is typically employed only as an emergency remedy, for example, as a temporary workaround to a library misconâ
figuration issue.)
lib*.so*
shared objects
NOTES
Legacy Hardware capabilities (from glibc 2.5 to glibc 2.37)
Some shared objects are compiled using hardware-specific instructions which do not exist on every CPU. Such objects
should be installed in directories whose names define the required hardware capabilities, such as /usr/lib/sse2/.
The dynamic linker checks these directories against the hardware of the machine and selects the most suitable version
of a given shared object. Hardware capability directories can be cascaded to combine CPU features. The list of supâ
ported hardware capability names depends on the CPU. The following names are currently recognized:
Alpha ev4, ev5, ev56, ev6, ev67
MIPS loongson2e, loongson2f, octeon, octeon2
PowerPC
4xxmac, altivec, arch_2_05, arch_2_06, booke, cellbe, dfp, efpdouble, efpsingle, fpu, ic_snoop, mmu, notb,
pa6t, power4, power5, power5+, power6x, ppc32, ppc601, ppc64, smt, spe, ucache, vsx
SPARC flush, muldiv, stbar, swap, ultra3, v9, v9v, v9v2
s390 dfp, eimm, esan3, etf3enh, g5, highgprs, hpage, ldisp, msa, stfle, z900, z990, z9-109, z10, zarch
x86 (32-bit only)
acpi, apic, clflush, cmov, cx8, dts, fxsr, ht, i386, i486, i586, i686, mca, mmx, mtrr, pat, pbe, pge, pn,
pse36, sep, ss, sse, sse2, tm
The legacy hardware capabilities support has the drawback that each new feature added grows the search path exponenâ
tially, because it has to be added to every combination of the other existing features.
For instance, on x86 32-bit, if the hardware supports i686 and sse2, the resulting search path will be
i686/sse2:i686:sse2:.. A new capability newcap will set the search path to newcap/i686/sse2:newcap/i686:newâ
cap/sse2:newcap:i686/sse2:i686:sse2:.
glibc Hardware capabilities (from glibc 2.33)
glibc 2.33 added a new hardware capability scheme,
where under each CPU architecture, certain levels can be defined, grouping support for certain features or
special instructions. Each architecture level has a fixed set of paths that it adds to the dynamic linker
search list, depending on the hardware of the machine. Since each new architecture level is not combined with
previously existing ones, the new scheme does not have the drawback of growing the dynamic linker search list
uncontrollably.
For instance, on x86 64-bit, if the hardware supports x86_64-v3 (for instance Intel Haswell or AMD Excavator), the
resulting search path will be glibc-hwcaps/x86-64-v3:glibc-hwcaps/x86-64-v2:. The following paths are currently supâ
ported, in priority order.
PowerPC (64-bit little-endian only)
power10, power9
s390 (64-bit only)
z16, z15, z14, z13
x86 (64-bit only)
x86-64-v4, x86-64-v3, x86-64-v2
glibc 2.37 removed support for the legacy hardware capabilities.
SEE ALSO
ld(1), ldd(1), pldd(1), sprof(1), dlopen(3), getauxval(3), elf(5), capabilities(7), rtld-audit(7), ldconfig(8),
sln(8)
Linux man-pages 6.17 2026-02-08 ld.so(8)