The ldd command lists the dynamic libraries used by a program. This utility is very useful to find out what shared libraries your executables depend on or to do some basic forensic analysis or to help you building chrooted jails.
Simply type this…
ldd /usr/bin/passwd
and you’ll get something like this…
linux-gate.so.1 => (0xffffe000)
libcrypt.so.1 => /lib/libcrypt.so.1 (0xb7fb5000)
libpam.so.0 => /lib/libpam.so.0 (0xb7fab000)
libpam_misc.so.0 => /lib/libpam_misc.so.0 (0xb7fa8000)
libcrack.so.2 => /lib/libcrack.so.2 (0xb7f9c000)
libc.so.6 => /lib/libc.so.6 (0xb7e87000)
libdl.so.2 => /lib/libdl.so.2 (0xb7e83000)
/lib/ld-linux.so.2 (0xb7feb000)