man1/ldd.1

   1 .\" Copyright 1995-2000 David Engel (david@ods.com)
   2 .\" Copyright 1995 Rickard E. Faith (faith@cs.unc.edu)
   3 .\" Copyright 2000 Ben Collins (bcollins@debian.org)
   4 .\"    Redone for GLibc 2.2
   5 .\" Copyright 2000 Jakub Jelinek (jakub@redhat.com)
   6 .\"    Corrected.
   7 .\" and Copyright (C) 2012, 2016, Michael Kerrisk <mtk.manpages@gmail.com>
   8 .\"
   9 .\" %%%LICENSE_START(GPL_NOVERSION_ONELINE)
  10 .\" Do not restrict distribution.
  11 .\" May be distributed under the GNU General Public License
  12 .\" %%%LICENSE_END
  13 .\"
  14 .TH LDD 1 2019-03-06 "" "Linux Programmer's Manual"
  15 .SH NAME
  16 ldd \- print shared object dependencies
  17 .SH SYNOPSIS
  18 .BR ldd " [\fIoption\fP]... \fIfile\fP..."
  19 .SH DESCRIPTION
  20 .B ldd
  21 prints the shared objects (shared libraries) required by each program or
  22 shared object specified on the command line.
  23 An example of its use and output is the following:
  24 .PP
  25 .in +2n
  26 .EX
  27 $ \fBldd /bin/ls\fP
  28         linux-vdso.so.1 (0x00007ffcc3563000)
  29         libselinux.so.1 => /lib64/libselinux.so.1 (0x00007f87e5459000)
  30         libcap.so.2 => /lib64/libcap.so.2 (0x00007f87e5254000)
  31         libc.so.6 => /lib64/libc.so.6 (0x00007f87e4e92000)
  32         libpcre.so.1 => /lib64/libpcre.so.1 (0x00007f87e4c22000)
  33         libdl.so.2 => /lib64/libdl.so.2 (0x00007f87e4a1e000)
  34         /lib64/ld-linux-x86-64.so.2 (0x00005574bf12e000)
  35         libattr.so.1 => /lib64/libattr.so.1 (0x00007f87e4817000)
  36         libpthread.so.0 => /lib64/libpthread.so.0 (0x00007f87e45fa000)
  37 .EE
  38 .in
  39 .PP
  40 In the usual case,
  41 .B ldd
  42 invokes the standard dynamic linker (see
  43 .BR ld.so (8))
  44 with the
  45 .B LD_TRACE_LOADED_OBJECTS
  46 environment variable set to 1.
  47 This causes the dynamic linker to inspect the program's dynamic dependencies,
  48 and find (according to the rules described in
  49 .BR ld.so (8))
  50 and load the objects that satisfy those dependencies.
  51 For each dependency,
  52 .B ldd
  53 displays the location of the matching object
  54 and the (hexadecimal) address at which it is loaded.
  55 (The
  56 .I linux-vdso
  57 and
  58 .I ld-linux
  59 shared dependencies are special; see
  60 .BR vdso (7)
  61 and
  62 .BR ld.so (8).)
  63 .\"
  64 .SS Security
  65 Be aware that in some circumstances
  66 (e.g., where the program specifies an ELF interpreter other than
  67 .IR ld-linux.so ),
  68 .\" The circumstances are where the program has an interpreter
  69 .\" other than ld-linux.so. In this case, ldd tries to execute the
  70 .\" program directly with LD_TRACE_LOADED_OBJECTS=1, with the
  71 .\" result that the program interpreter gets control, and can do
  72 .\" what it likes, or pass control to the program itself.
  73 .\" Much more detail at
  74 .\" http://www.catonmat.net/blog/ldd-arbitrary-code-execution/
  75 some versions of
  76 .B ldd
  77 may attempt to obtain the dependency information
  78 by attempting to directly execute the program,
  79 which may lead to the execution of whatever code is defined
  80 in the program's ELF interpreter,
  81 and perhaps to execution of the program itself.
  82 .\" Mainline glibc's ldd allows this possibility (the line
  83 .\"      try_trace "$file"
  84 .\" in glibc 2.15, for example), but many distro versions of
  85 .\" ldd seem to remove that code path from the script.
  86 (In glibc versions before 2.27,
  87 .\" glibc commit eedca9772e99c72ab4c3c34e43cc764250aa3e3c
  88 the upstream
  89 .B ldd
  90 implementation did this for example,
  91 although most distributions provided a modified version that did not.)
  92 .PP
  93 Thus, you should
  94 .I never
  95 employ
  96 .B ldd
  97 on an untrusted executable,
  98 since this may result in the execution of arbitrary code.
  99 A safer alternative when dealing with untrusted executables is:
 100 .PP
 101 .in +4n
 102 .EX
 103 $ \fBobjdump \-p /path/to/program | grep NEEDED\fP
 104 .EE
 105 .in
 106 .PP
 107 Note, however, that this alternative shows only the direct dependencies
 108 of the executable, while
 109 .B ldd
 110 shows the entire dependency tree of the executable.
 111 .SH OPTIONS
 112 .TP
 113 .B \-\-version
 114 Print the version number of
 115 .BR ldd .
 116 .TP
 117 .BR \-v ", " \-\-verbose
 118 Print all information, including, for example,
 119 symbol versioning information.
 120 .TP
 121 .BR \-u ", " \-\-unused
 122 Print unused direct dependencies.
 123 (Since glibc 2.3.4.)
 124 .TP
 125 .BR \-d ", " \-\-data\-relocs
 126 Perform relocations and report any missing objects (ELF only).
 127 .TP
 128 .BR \-r ", " \-\-function\-relocs
 129 Perform relocations for both data objects and functions, and
 130 report any missing objects or functions (ELF only).
 131 .TP
 132 .B \-\-help
 133 Usage information.
 134 .\" .SH NOTES
 135 .\" The standard version of
 136 .\" .B ldd
 137 .\" comes with glibc2.
 138 .\" Libc5 came with an older version, still present
 139 .\" on some systems.
 140 .\" The long options are not supported by the libc5 version.
 141 .\" On the other hand, the glibc2 version does not support
 142 .\" .B \-V
 143 .\" and only has the equivalent
 144 .\" .BR \-\-version .
 145 .\" .LP
 146 .\" The libc5 version of this program will use the name of a library given
 147 .\" on the command line as-is when it contains a \(aq/\(aq; otherwise it
 148 .\" searches for the library in the standard locations.
 149 .\" To run it
 150 .\" on a shared library in the current directory, prefix the name with "./".
 151 .SH BUGS
 152 .B ldd
 153 does not work on a.out shared libraries.
 154 .PP
 155 .B ldd
 156 does not work with some extremely old a.out programs which were
 157 built before
 158 .B ldd
 159 support was added to the compiler releases.
 160 If you use
 161 .B ldd
 162 on one of these programs, the program will attempt to run with
 163 .I argc
 164 = 0 and the results will be unpredictable.
 165 .\" .SH AUTHOR
 166 .\" David Engel.
 167 .\" Roland McGrath and Ulrich Drepper.
 168 .SH SEE ALSO
 169 .BR pldd (1),
 170 .BR sprof (1),
 171 .BR ld.so (8),
 172 .BR ldconfig (8)