|LDD(1)||Linux Programmer's Manual||LDD(1)|
$ ldd /bin/ls 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)
In the usual case, ldd invokes the standard dynamic linker (see ld.so(8)) with the 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 ld.so(8)) and load the objects that satisfy those dependencies. For each dependency, ldd displays the location of the matching object and the (hexadecimal) address at which it is loaded. (The linux-vdso and ld-linux shared dependencies are special; see vdso(7) and ld.so(8).)
Thus, you should never employ 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
Note, however, that this alternative shows only the direct dependencies of the executable, while ldd shows the entire dependency tree of the executable.
ldd does not work with some extremely old a.out programs which were built before ldd support was added to the compiler releases. If you use ldd on one of these programs, the program will attempt to run with argc = 0 and the results will be unpredictable.