How to hard code a dynamic library path on Linux

Question

I would like to hard code the path to a library in my executable, in Linux. On OS X this is achieved by providing the full path after the -o argument when building the library. For example, I build a library like this on OS X:

cc foo.c --shared -o /home/sander/libfoo.so

When I build an executable called 'bar' that links with this library, and I use otool -L on the executable, I get this output:

bar:
    /home/sander/libfoo.so (compatibility version 0.0.0, current version 0.0.0)

I can now run this executable from anywhere, and it is always able to find the library.

I am looking for equivalent functionality on Linux with gcc. I'd rather not use rpath since that doesn't link to a specific library + path.

Is there a reason you can't just link statically? If you're concerned about things being moved, that would seem far the safer option. — David Roundy
– David Roundy, Commented May 9, 2015 at 19:20
I can't link statically. This functionality is part of a package management system, and I must be able to update individual packages. I am not as much concerned about the libraries being moved. What's more important is that I can find the libraries from anywhere on my system. — Sander Mertens
– Sander Mertens, Commented May 9, 2015 at 19:35

Johannes Weiss · Accepted Answer · 2015-05-09 20:30:58Z

6

Just compile it this way, so don't use -llib but specify it as object to compile:

cd /full/path/to/lib
gcc -shared -fpic -o liblib.so lib.c             # make the lib
gcc -c -o prog.o prog.c                          # compile program
gcc -o prog prog.o "/full/path/to/lib/liblib.so" # link everything together

EDIT: I initially wrote that on OS X it would not matter whether an absolute or relative path is specified after the -o option. That is not true. It does affect the library's "name" in the Mach-O LC_ID_DYLIB load command. Thanks @Sander Mertens for letting me know.

edited May 9, 2015 at 20:30

answered May 9, 2015 at 19:37

Johannes Weiss

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2 Comments

Sander Mertens Over a year ago

Thanks, that worked! I disagree on -o though. otool reveals that whatever you specify after -o is used when linking with that library. I just verified it again on OS X, and depending on the argument of -o, otool shows different output.

Johannes Weiss Over a year ago

@SanderMertens sorry about that and thanks for letting me know. Editing the answer.

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