Debugging native library dependencies on Linux

.NET Core apps can run on a number of operating systems. When using purely .NET libraries, deployment is a breeze. However, if you're using a library that wraps a native (C/C++) library, then you might have come across this error message when trying to run your app on Linux:

System.TypeInitializationException: The type initializer for 'DlibDotNet.NativeMethods' threw an exception.
 ---> System.DllNotFoundException: Unable to load shared library 'DlibDotNetNativeDnn' or one of its dependencies. In order to help diagnose loading problems, consider setting the LD_DEBUG environment variable: libDlibDotNetNativeDnn: cannot open shared object file: No such file or directory

This tells us that either libDlibDotNetNativeDnn.so doesn't exist (which in my case it did), or it has some other native dependencies that are missing.

To see which dependencies are missing, you use ldd:

ldd libDlibDotNetNativeDnn.so

And it would give you an output like this:

linux-vdso.so.1 (0x00007ffdb9fe1000)
libpthread.so.0 => /lib/x86_64-linux-gnu/libpthread.so.0 (0x00007f06b2254000)
libopenblas.so.0 => not found
libstdc++.so.6 => /lib/x86_64-linux-gnu/libstdc++.so.6 (0x00007f06b2072000)
libm.so.6 => /lib/x86_64-linux-gnu/libm.so.6 (0x00007f06b1f24000)
libgcc_s.so.1 => /lib/x86_64-linux-gnu/libgcc_s.so.1 (0x00007f06b1f0a000)
libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007f06b1d1d000)
/lib64/ld-linux-x86-64.so.2 (0x00007f06b490d000)

Now it's clear that libopenblas is missing from the system. Search for it on google and find the package that contains the library. In libopenblas's case, it happens to be in the libopenblas-base . To install it on ubuntu, you can run:

sudo apt-get install libopenblas-base

Tada 🎉 and now your app (hopefully) works as expected!

This little error wasted several hours from me. I am grateful to the people who maintain these native library wrappers and hide (most of) the ugliness from us.