Determine direct shared object dependencies of a Linux binary?

How can I easily find out the direct shared object dependencies of a Linux binary in ELF format?

I'm aware of the ldd tool, but that appears to output all dependencies of a binary, including the dependencies of any shared objects that binary is dependent on.

You can use readelf to explore the ELF headers. readelf -d will list the direct dependencies as NEEDED sections.

 $ readelf -d elfbin

Dynamic section at offset 0xe30 contains 22 entries:
  Tag        Type                         Name/Value
 0x0000000000000001 (NEEDED)             Shared library: [libssl.so.1.0.0]
 0x0000000000000001 (NEEDED)             Shared library: [libc.so.6]
 0x000000000000000c (INIT)               0x400520
 0x000000000000000d (FINI)               0x400758
 ...

If you want to find dependencies recursively (including dependencies of dependencies, dependencies of dependencies of dependencies and so on)…

You may use ldd command. ldd - print shared library dependencies

The objdump tool can tell you this information. If you invoke objdump with the -x option, to get it to output all headers then you'll find the shared object dependencies right at the start in the "Dynamic Section".

For example running objdump -x /usr/lib/libXpm.so.4 on my system gives the following information in the "Dynamic Section":

Dynamic Section:
  NEEDED               libX11.so.6
  NEEDED               libc.so.6
  SONAME               libXpm.so.4
  INIT                 0x0000000000002450
  FINI                 0x000000000000e0e8
  GNU_HASH             0x00000000000001f0
  STRTAB               0x00000000000011a8
  SYMTAB               0x0000000000000470
  STRSZ                0x0000000000000813
  SYMENT               0x0000000000000018
  PLTGOT               0x000000000020ffe8
  PLTRELSZ             0x00000000000005e8
  PLTREL               0x0000000000000007
  JMPREL               0x0000000000001e68
  RELA                 0x0000000000001b38
  RELASZ               0x0000000000000330
  RELAENT              0x0000000000000018
  VERNEED              0x0000000000001ad8
  VERNEEDNUM           0x0000000000000001
  VERSYM               0x00000000000019bc
  RELACOUNT            0x000000000000001b

The direct shared object dependencies are listing as 'NEEDED' values. So in the example above, libXpm.so.4 on my system just needs libX11.so.6 and libc.so.6.

It's important to note that this doesn't mean that all the symbols needed by the binary being passed to objdump will be present in the libraries, but it does at least show what libraries the loader will try to load when loading the binary.

ldd -v prints the dependency tree under "Version information:' section. The first block in that section are the direct dependencies of the binary.

See Hierarchical ldd(1)