ldd.1: Add more detail on the output of ldd

[thirdparty/man-pages.git] / man1 / ldd.1

.\" Copyright 1995-2000 David Engel (david@ods.com)
.\" Copyright 1995 Rickard E. Faith (faith@cs.unc.edu)
.\" Copyright 2000 Ben Collins (bcollins@debian.org)
.\"    Redone for GLibc 2.2
.\" Copyright 2000 Jakub Jelinek (jakub@redhat.com)
.\"    Corrected.
.\" Most of this was copied from the README file.
.\"
.\" %%%LICENSE_START(GPL_NOVERSION_ONELINE)
.\" Do not restrict distribution.
.\" May be distributed under the GNU General Public License
.\" %%%LICENSE_END
.\"
.TH LDD 1 2015-08-08 "" "Linux Programmer's Manual"
.SH NAME
ldd \- print shared object dependencies
.SH SYNOPSIS
.BR ldd " [\fIoption\fP]... \fIfile\fP..."
.SH DESCRIPTION
.B ldd
prints the shared objects (shared libraries) required by each program or
shared object specified on the command line.
An example of its use and output is the following:

.nf

$ \fBldd /bin/ls\fP
        linux-vdso.so.1 (0x00007ffcc3563000)
        libselinux.so.1 => /lib64/libselinux.so.1 (0x00007f87e5459000)
        libcap.so.2 => /lib64/libcap.so.2 (0x00007f87e5254000)
        libc.so.6 => /lib64/libc.so.6 (0x00007f87e4e92000)
        libpcre.so.1 => /lib64/libpcre.so.1 (0x00007f87e4c22000)
        libdl.so.2 => /lib64/libdl.so.2 (0x00007f87e4a1e000)
        /lib64/ld-linux-x86-64.so.2 (0x00005574bf12e000)
        libattr.so.1 => /lib64/libattr.so.1 (0x00007f87e4817000)
        libpthread.so.0 => /lib64/libpthread.so.0 (0x00007f87e45fa000)
.fi

In the usual case,
.B ldd
invokes the standard dynamic linker (see
.BR ld.so (8))
with the
.B LD_TRACE_LOADED_OBJECTS
environment variable set to 1.
This causes the dynamic linker to inspect the program's dynamic dependencies,
and find (according to the rules described in
.BR ld.so (8))
and load the objects that satisfy those dependencies.
For each dependency,
.BR ldd
displays the location of the matching object
and the (hexadecimal) address at which it is loaded.
(The
.I linux-vdso
and
.I ld-linux
shared dependencies are special; see
.BR vdso (7)
and
.BR ld.so (8).)
.\"
.SS Security
Be aware that in some circumstances, some versions of
.BR ldd
may attempt to obtain the dependency information
by directly executing the program.
.\" Mainline glibc's ldd allows this possibility (the line
.\"      try_trace "$file"
.\" in glibc 2.15, for example), but many distro versions of
.\" ldd seem to remove that code path from the script.
Thus, you should
.I never
employ
.B ldd
on an untrusted executable,
since this may result in the execution of arbitrary code.
A safer alternative when dealing with untrusted executables is:

    $ objdump \-p /path/to/program | grep NEEDED
.SH OPTIONS
.TP
.B \-\-version
Print the version number of
.BR ldd .
.TP
.BR \-v ", " \-\-verbose
Print all information, including, for example,
symbol versioning information.
.TP
.BR \-u ", " \-\-unused
Print unused direct dependencies.
(Since glibc 2.3.4.)
.TP
.BR \-d ", " \-\-data\-relocs
Perform relocations and report any missing objects (ELF only).
.TP
.BR \-r ", " \-\-function\-relocs
Perform relocations for both data objects and functions, and
report any missing objects or functions (ELF only).
.TP
.B \-\-help
Usage information.
.\" .SH NOTES
.\" The standard version of
.\" .B ldd
.\" comes with glibc2.
.\" Libc5 came with an older version, still present
.\" on some systems.
.\" The long options are not supported by the libc5 version.
.\" On the other hand, the glibc2 version does not support
.\" .B \-V
.\" and only has the equivalent
.\" .BR \-\-version .
.\" .LP
.\" The libc5 version of this program will use the name of a library given
.\" on the command line as-is when it contains a \(aq/\(aq; otherwise it
.\" searches for the library in the standard locations.
.\" To run it
.\" on a shared library in the current directory, prefix the name with "./".
.SH BUGS
.B ldd
does not work on a.out shared libraries.
.PP
.B ldd
does not work with some extremely old a.out programs which were
built before
.B ldd
support was added to the compiler releases.
If you use
.B ldd
on one of these programs, the program will attempt to run with
.I argc
= 0 and the results will be unpredictable.
.\" .SH AUTHOR
.\" David Engel.
.\" Roland McGrath and Ulrich Drepper.
.SH SEE ALSO
.BR pldd (1),
.BR sprof (1),
.BR ld.so (8),
.BR ldconfig (8)