Can't access shared libraries when running with sudo

Question

I'm trying to get a demo working writing PCM to the I²S; I've created a small demo program that gives an error when I run with the following command ./demo stereo_small.wav

can't open /dev/mem

So I run with the this command sudo ./demo stereo_small.wav (added sudo) and the demo should now be able to run successfully with elevated privileges.

But I now get this error:

./demo: error while loading shared libraries: libsndfile.so.1: cannot open shared object file: No such file or directory

Initially to get the program working I had to execute this command export LD_LIBRARY_PATH=/usr/local/lib to get it to work, but the error has now retuned but only when I prefix with sudo

Please bare with me I've only been using C & Linux for a few hours!

Here's what i've done to compile and run:

gcc `pkg-config --cflags sndfile` -c demo.c
gcc 'pkg-config --libs sndfile' demo.o -o demo
sudo ./demo stereo_small.wav

Update - Cause: some environment variables aren't maintained under the SU context see here

Answer 1

It's a bit of a hack until I figure out how to compile and link correctly or move the requirement for sudo from the 'finished' code; but here is one option...

run the shell under sudo and add set the environment variable before executing the program:

sudo bash
export LD_LIBRARY_PATH=/usr/local/lib
./demo stereo_small.wav

Answer 2

If you use su instead of sudo then you can pass a command to the root shell for it to execute:

su --command="export LD_LIBRARY_PATH=/usr/local/lib && ./demo stereo_small.wav"

The problem with using sudo is that the variable we're trying to export does persist across to the root shell. I'm not really sure why.