Can't find .so in the same directory as the executable?
Solution 1:
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 2:
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 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.