The ldd (List Dynamic Dependencies) command in Linux is used to display shared library dependencies of an executable or a shared object (.so file). It helps in debugging missing dependencies, checking linked libraries, and troubleshooting runtime issues.

1. Check Shared Libraries for an Executable

ldd /bin/ls

✔ What it does:

• Lists all shared libraries (.so files) required by /bin/ls.

📌 Example Output:

linux-vdso.so.1 (0x00007ffd7d9f0000)
libselinux.so.1 => /lib/x86_64-linux-gnu/libselinux.so.1 (0x00007f3e6d8d0000)
libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007f3e6d6c0000)

💡 Useful for checking dependencies before running an application.

2. Check Shared Libraries for a Shared Object (.so file)

ldd /lib/x86_64-linux-gnu/libc.so.6

✔ What it does:

• Displays dependencies of the libc.so.6 shared library.

📌 Example Output:

/lib/x86_64-linux-gnu/libc.so.6:
        linux-vdso.so.1 (0x00007ffd7d9f0000)
        /lib64/ld-linux-x86-64.so.2 (0x00007f3e6d6c0000)

💡 Helps in debugging shared object dependencies.

3. Find Missing Dependencies

ldd /usr/bin/program | grep "not found"

✔ What it does:

• Identifies missing libraries for an executable.

📌 Example Output:

libssl.so.1.1 => not found
libcrypto.so.1.1 => not found

💡 Useful for troubleshooting missing library errors.

4. Check Dependencies for a Custom Binary

ldd /home/user/my_program

✔ What it does:

• Displays shared libraries required by custom binaries.

📌 Use case:

• Before deploying an application, check which libraries are required on another system.

5. Display Only Paths of Shared Libraries

ldd /bin/bash | awk '{print $3}'

✔ What it does:

• Extracts only the paths of the shared libraries.

📌 Example Output:

/lib/x86_64-linux-gnu/libtinfo.so.6
/lib/x86_64-linux-gnu/libc.so.6
/lib64/ld-linux-x86-64.so.2

💡 Useful for listing all linked libraries in a script.

6. List Dependencies for a Python Interpreter

ldd $(which python3)

✔ What it does:

• Shows all libraries required by Python.

📌 Example Output:

libpthread.so.0 => /lib/x86_64-linux-gnu/libpthread.so.0
libdl.so.2 => /lib/x86_64-linux-gnu/libdl.so.2

💡 Helps when debugging Python runtime issues.

7. Find Dependencies for a Java Virtual Machine (JVM)

ldd $(which java)

✔ What it does:

• Displays required libraries for the Java runtime environment.

📌 Use case:

• Identify if a missing library is causing Java to fail.

8. Find Which Library Provides a Missing Dependency

ldd /usr/bin/ffmpeg | grep "not found"
ldconfig -p | grep libavcodec

✔ What it does:

• The first command finds missing dependencies.
• The second command searches for the missing library.

📌 Example Output (if missing library found):

libavcodec.so.58 (libavcodec.so.58 -> /usr/lib/x86_64-linux-gnu/libavcodec.so.58)

💡 Useful for resolving broken dependencies in multimedia software.

9. Check Dependencies of a Statically Linked Binary

ldd /bin/busybox

📌 Example Output (if statically linked):

not a dynamic executable

✔ What it means:

• BusyBox is statically linked, meaning all libraries are compiled inside the binary.

💡 Useful when working with lightweight embedded Linux systems.

10. Debug ELF Binaries with LD_TRACE_LOADED_OBJECTS

LD_TRACE_LOADED_OBJECTS=1 /usr/bin/bash

✔ What it does:

• Alternative to ldd, directly traces loaded libraries.

📌 Example Output:

linux-vdso.so.1 =>  (0x00007ffd7d9f0000)
libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007f3e6d6c0000)

💡 Useful when ldd is not available or for debugging manually.

Final Thoughts

• ldd is essential for debugging shared library dependencies.
• Always check missing dependencies (grep "not found").
• Use ldconfig -p to find missing libraries.