ldd

Display shared library dependencies of a binary

$ ldd [path/to/binary]

$ ldd [[-v|--verbose]] [path/to/binary]

$ ldd [[-u|--unused]] [path/to/binary]

$ ldd [[-d|--data-relocs]] [path/to/binary]

$ ldd [[-r|--function-relocs]] [path/to/binary]

ldd [option]... file...

-h, --help
    Display this help message and exit

-V, --version
    Print version information and exit

-v, --verbose
    Verbose mode: print all details, including symbol versioning

-u, --unused
    Print unused direct dependencies

-r, --function-relocs
    Print relocation processing information for functions

-d, --data-relocs
    Print relocation processing for data objects

-R, --text-relocs
    Print relocation processing for text/code

--list
    Equivalent to -r -d -R (list all relocations)

-I, --ignore-missing
    Ignore missing libraries and continue

The ldd command displays the shared libraries required by an ELF executable, shared object, or core dump file. It is invaluable for diagnosing linking issues, verifying dependencies for portability, and understanding runtime library needs.

ldd achieves this by invoking the dynamic linker/loader (ld.so or ld-linux.so) with the environment variable LD_TRACE_LOADED_OBJECTS set to 1. This simulates program execution but traces library loading instead of running the main code. Output shows each library, its full path, and memory address, e.g., libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007f8b2c000000).

Use cases include checking for missing libraries before deployment, identifying version mismatches, or auditing dependencies in containers. It works on dynamically linked ELF binaries but fails on static executables (showing 'not a dynamic executable') or non-ELF files. For verbose details like symbol versions or relocations, use options like -v.

ldd executes untrusted binaries via the dynamic linker, posing a security risk if the file contains malicious code. Avoid using on untrusted inputs. Does not support a.out binaries or fully static executables. Combining certain relocation flags (-r/-d/-R) with -u is invalid.

/bin/ls
linux-vdso.so.1 (0x00007ffc12345000)
libselinux.so.1 => /lib/x86_64-linux-gnu/libselinux.so.1 (0x00007f8b2c123000)
libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007f8b2c000000)
/lib64/ld-linux-x86-64.so.2 (0x00007f8b2c600000)

For safer inspection without execution, use readelf -d file | grep NEEDED or objdump -p file | grep NEEDED to list required libraries statically.

Introduced with GNU C Library (glibc) in the early 1990s alongside ELF support. Evolved with glibc versions to add relocation tracing (glibc 2.3+), verbose symbol info, and security mitigations. Widely used on Linux systems; BSD variants exist as ldd or lddtree.

ld.so(8), readelf(1), objdump(1), ldconfig(8)