I came across a reference to it recently on proggit and (as of now) it is not explained.
I suspect this might be it, but I don't know for sure.
9 Answers
If you set LD_PRELOAD to the path of a shared object, that file will be loaded before any other library (including the C runtime, libc.so). So to run ls with your special malloc() implementation, do this:
$ LD_PRELOAD=/path/to/my/malloc.so /bin/ls
You can override symbols in the stock libraries by creating a library with the same symbols and specifying the library in LD_PRELOAD.
Some people use it to specify libraries in nonstandard locations, but LD_LIBRARY_PATH is better for that purpose.
With LD_PRELOAD you can give libraries precedence.
For example you can write a library which implement malloc and free. And by loading these with LD_PRELOAD your malloc and free will be executed rather than the standard ones.
When LD_PRELOAD is used, that file will be loaded before any other. Use
$export LD_PRELOAD=/path/lib for lib to be pre-loaded. This can even be used in programs too.
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