specifying new directory in /etc/ld.so.conf does not seem to work

[quickk]

Hi everyone,

I'm trying to use a minimum perfect hash library called cmph. I've compiled it and installed the library to the folder /opt/local/lib. Then I added that folder to the /etc/ld.so.conf file like this:


/opt/local/lib
include /etc/ld.so.conf.d/*.conf


(that last line was already there)

I then ran "sudo ldconfig" to refresh the library cache.

The problem is that when I try to compile my program, I get the message that the cmph library cannot be found


mpiifort -fPIC -o sim sim.f90 kinds_module.o variables_module.o basis_module.o Hamiltonian_module.o mph.o -lcmph
ld: cannot find -lcmph


However when I instead use the -L/opt/local/lib option everything works great: (I get no errors, and can run my program)


mpiifort -fPIC -o sim sim.f90 kinds_module.o variables_module.o basis_module.o Hamiltonian_module.o mph.o -L/opt/local/lib -lcmph

I obviously don't understand something. I thought that both approaches would work equally well. Any comments?

[soltanis]

Not entirely sure but it might be that ldconfig sets LD_LIBRARY_PATH, so consider restarting your shell and seeing if that changes anything.

[johnl]

At compile time, the compile-time linker, ld, needs to know where to find shared libraries to link to. This is specified, as you noticed, with the -L/path/to/lib argument to ld. You can view the default arguments for this with gcc -print-search-dirs.

At runtime, the OS needs to know where shared libraries linked to an executable can be found so that they can be loaded when the program is executed. This is specified in LD_LIBRARY_PATH or ld.so.conf.

These configurations don't overlap, so you will need to do both.

[quickk]

Thank you jonhl! That made perfect sense. You wouldn't believe much time I've spent trying to understand this. I'm slowly getting learning the ropes, but I still have a long way to go.

[dwhitney67]

This is specified in LD_LIBRARY_PATH or ld.so.conf.

These configurations don't overlap, so you will need to do both.

The word "or" in your first statement contradicts what you state in your second statement.

The use of LD_LIBRARY_PATH is only required for library paths that are NOT in the ld cache. One can verify what paths (and hence libraries) are in the ld-cache by running the ldconfig command with the -v option.

As for the OP editing /etc/ld.so.conf, personally I would have recommended that he create a file in /etc/ld.so.conf.d directory that contains the library path that is required. Then run ldconfig (with the -v option) to verify that the library has been found and placed in the cache.

[johnl]

The word "or" in your first statement contradicts what you state in your second statement.

The use of LD_LIBRARY_PATH is only required for library paths that are NOT in the ld cache. One can verify what paths (and hence libraries) are in the ld-cache by running the ldconfig command with the -v option.

As for the OP editing /etc/ld.so.conf, personally I would have recommended that he create a file in /etc/ld.so.conf.d directory that contains the library path that is required. Then run ldconfig (with the -v option) to verify that the library has been found and placed in the cache.

Sorry, that was unclear; what I meant was:


pass_dash_L_to_ld && (specify_LD_LIBRARY_PATH || add_entry_to_ld.so.conf)

You need to do both the first step and one of the latter steps.