.\" This is in the public domain
.\" %%%LICENSE_END
.\"
-.TH LD.SO 8 2017-09-15 "GNU" "Linux Programmer's Manual"
+.TH LD.SO 8 2019-08-02 "GNU" "Linux Programmer's Manual"
.SH NAME
ld.so, ld\-linux.so \- dynamic linker/loader
.SH SYNOPSIS
.PP
The program
.B ld.so
-handles a.out binaries, a format used long ago;
+handles a.out binaries, a binary format used long ago.
+The program
.B ld\-linux.so*
(\fI/lib/ld\-linux.so.1\fP for libc5, \fI/lib/ld\-linux.so.2\fP for glibc2)
-handles ELF,
-which everybody has been using for years now.
-Otherwise, both have the same behavior, and use the same
-support files and programs as
-.BR ldd (1),
+handles binaries that are in the more modern ELF format.
+Both programs have the same behavior, and use the same
+support files and programs
+.RB ( ldd (1),
.BR ldconfig (8),
and
-.IR /etc/ld.so.conf .
+.IR /etc/ld.so.conf ).
.PP
When resolving shared object dependencies,
the dynamic linker first inspects each dependency
Use of DT_RPATH is deprecated.
.IP o
Using the environment variable
-.BR LD_LIBRARY_PATH
-(unless the executable is being run in secure-execution mode; see below).
-in which case it is ignored.
+.BR LD_LIBRARY_PATH ,
+unless the executable is being run in secure-execution mode (see below),
+in which case this variable is ignored.
.IP o
Using the directories specified in the
DT_RUNPATH dynamic section attribute
.\" Don't do this!!
.SH OPTIONS
.TP
-.B \-\-list
-List all dependencies and how they are resolved.
-.TP
-.B \-\-verify
-Verify that program is dynamically linked and this dynamic linker can handle
-it.
+.BI \-\-audit " list"
+Use objects named in
+.I list
+as auditors.
+The objects in
+.I list
+are delimited by colons.
.TP
.B \-\-inhibit\-cache
Do not use
Ignore RPATH and RUNPATH information in object names in
.IR list .
This option is ignored when running in secure-execution mode (see below).
+The objects in
+.I list
+are delimited by colons or spaces.
.TP
-.BI \-\-audit " list"
-Use objects named in
+.B \-\-list
+List all dependencies and how they are resolved.
+.TP
+.BR \-\-preload " \fIlist\fP (since glibc 2.30)"
+Preload the objects specified in
+.IR list .
+The objects in
.I list
-as auditors.
+are delimited by colons or spaces.
+The objects are preloaded as explained in the description of the
+.BR LD_PRELOAD
+environment variable below.
+.IP
+By contrast with
+.BR LD_PRELOAD ,
+the
+.BR \-\-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.
+.TP
+.B \-\-verify
+Verify that program is dynamically linked and this dynamic linker can handle
+it.
.SH ENVIRONMENT
Various environment variables influence the operation of the dynamic linker.
.\"
.SS Secure-execution mode
For security reasons,
-the effects of some environment variables are voided or modified if
-the dynamic linker determines that the binary should be
-run in secure-execution mode.
-(For details, see the discussion of individual environment variables below.)
+if the dynamic linker determines that a binary should be
+run in secure-execution mode,
+the effects 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 affect the operation of
+the dynamic linker itself, and are described below.
+Other environment variables treated in this way include:
+.BR GCONV_PATH ,
+.BR GETCONF_DIR ,
+.BR HOSTALIASES ,
+.BR LOCALDOMAIN ,
+.BR LOCPATH ,
+.BR MALLOC_TRACE ,
+.BR NIS_PATH ,
+.BR NLSPATH ,
+.BR RESOLV_HOST_CONF ,
+.BR RES_OPTIONS ,
+.BR TMPDIR ,
+and
+.BR TZDIR .
+.PP
A binary is executed in secure-execution mode if the
.B AT_SECURE
entry in the auxiliary vector (see
.B LD_LIBRARY_PATH
A list of directories in which to search for
ELF libraries at execution time.
-The items in the list are separated by either colons or semicolons.
-Similar to the
-.B PATH
-environment variable.
+The items in the list are separated by either colons or semicolons,
+and there is no support for escaping either separator.
.IP
This variable is ignored in secure-execution mode.
.IP
.B LD_PRELOAD
A list of additional, user-specified, ELF shared
objects to be loaded before all others.
-The items of the list can be separated by spaces or colons.
-This can be used to selectively override functions in other shared objects.
+This feature can be used to selectively override functions
+in other shared objects.
+.IP
+The items of the list can be separated by spaces or colons,
+and there is no support for escaping either separator.
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.
.IP
In secure-execution mode,
preload pathnames containing slashes are ignored.
.\"
.\" which will preload the libmod.so in 'lib' or 'lib64', using it
.\" in preference to the version in '.'.
+.IP
+There are various methods of specifying libraries to be preloaded,
+and these are handled in the following order:
+.RS
+.IP (1) 4
+The
+.BR LD_PRELOAD
+environment variable.
+.IP (2)
+The
+.B \-\-preload
+command-line option when invoking the dynamic linker directly.
+.IP (3)
+The
+.I /etc/ld.so.preload
+file (described below).
+.RE
.TP
.BR LD_TRACE_LOADED_OBJECTS
If set (to any value), causes the program to list its dynamic
many obsolete or only for internal use.
.TP
.BR LD_AUDIT " (since glibc 2.4)"
-A colon-separated list of user-specified, ELF shared objects
+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).
+would occur in the process)
These objects 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.
.IP
.B LD_AUDIT
is ignored in secure-execution mode.
and is typically employed only as an emergency remedy, for example,
as a temporary workaround to a library misconfiguration issue.)
.TP
-.B lib*.so*
+.I lib*.so*
shared objects
.PD
.SH NOTES
Hardware capability directories can be cascaded to combine CPU features.
The list of supported hardware capability names depends on the CPU.
The following names are currently recognized:
+.\" Presumably, this info comes from sysdeps/i386/dl-procinfo.c and
+.\" similar files
.TP
.B Alpha
ev4, ev5, ev56, ev6, ev67
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