Can't find .so in the same directory as the executable?

I have an executable which needs to link with libtest.so dynamically,so I put them in the same directory,then :

cd path_to_dir
./binary

But got this:

error while loading shared libraries: libtest.so: cannot open shared object file: No such file or directory

How can it be unable to find libtest.so which is already in the same directory as the executable itself?

Solution 1:

The loader never checks the current directory for shared objects unless it is explicitly directed to via $LD_LIBRARY_PATH. See the ld.so(8) man page for more details.

Solution 2:

While you can set LD_LIBRARY_PATH to let the dynamic linker know where to look, there are better options. You can put your shared library in one of the standard places, see /etc/ld.so.conf (on Linux) and /usr/bin/crle (on Solaris) for the list of these places

You can pass -R <path> to the linker when building your binary, which will add <path> to the list of directories scanned for your shared library. Here's an example. First, showing the problem:

libtest.h:

void hello_world(void);

libtest.c:

#include <stdio.h>
void hello_world(void) {
  printf("Hello world, I'm a library!\n");
}

hello.c:

#include "libtest.h"
int main(int argc, char **argv) {
  hello_world();
}

Makefile (tabs must be used):

all: hello
hello: libtest.so.0
%.o: %.c
        $(CC) $(CFLAGS) -fPIC -c -o $@ $<
libtest.so.0.0.1: libtest.o
        $(CC) -shared -Wl,-soname,libtest.so.0 -o libtest.so.0.0.1 libtest.o
libtest.so.0: libtest.so.0.0.1
        ln -s $< $@
clean:
        rm -f hello libtest.o hello.o libtest.so.0.0.1 libtest.so.0

Let's run it:

$ make
cc  -fPIC -c -o libtest.o libtest.c
cc -shared -Wl,-soname,libtest.so.0 -o libtest.so.0.0.1 libtest.o
ln -s libtest.so.0.0.1 libtest.so.0
cc     hello.c libtest.so.0   -o hello
$ ./hello 
./hello: error while loading shared libraries: libtest.so.0: cannot open shared object file: No such file or directory

How to fix it? Add -R <path> to the linker flags (here, by setting LDFLAGS).

$ make clean
(...)
$ make LDFLAGS="-Wl,-R -Wl,/home/maciej/src/tmp"
(...)
cc   -Wl,-R -Wl,/home/maciej/src/tmp  hello.c libtest.so.0   -o hello
$ ./hello 
Hello world, I'm a library!

Looking at the binary, you can see that it needs libtest.so.0:

$ objdump -p hello | grep NEEDED
  NEEDED               libtest.so.0
  NEEDED               libc.so.6

The binary will look for its libraries, apart from the standard places, in the specified directory:

$ objdump -p hello | grep RPATH
  RPATH                /home/maciej/src/tmp

If you want the binary to look in the current directory, you can set the RPATH to $ORIGIN. This is a bit tricky, because you need to make sure that the dollar sign is not interpreted by make. Here's one way to do it:

$ make CFLAGS="-fPIC" LDFLAGS="-Wl,-rpath '-Wl,\$\$ORIGIN'"
$ objdump -p hello | grep RPATH
  RPATH                $ORIGIN
$ ./hello 
Hello world, I'm a library!

Solution 3:

To load the shared objects from the same directory as your executable, simply execute:

$ LD_LIBRARY_PATH=. ./binary

Note: It will not modify the LD_LIBRARY_PATH variable of your system. The change only affects to this, and only this, execution of your program.

Solution 4:

For anyone using CMake for their build, you can set the CMAKE_EXE_LINKER_FLAGS to the following:

set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} -Wl,-rpath='$ORIGIN'")

This will properly propagate the linker flags for all build types (e.g., Debug, Release, etc...) to look for .so files in the current working directory first.

Solution 5:

For anyone that still struggles without an answer I found one myself with the following suggestion:

You could try updating the ld.so.cache using: sudo ldconfig -v

Worked for me.