How do you specify the location of libraries to a binary? (linux)

For a once-off, set the variable LD_LIBRARY_PATH to a colon-separated list of directories to search. This is analogous to PATH for executables, except that the standard system directories are additionally searched after the ones specified through the environment.

LD_LIBRARY_PATH=/usr/local/lib64 ./cart5

If you have a program that keeps libraries in a non-standard location and isn't able to find them on its own, you can write a wrapper script:

#!/bin/sh
if [ -n "$LD_LIBRARY_PATH" ]; then
  LD_LIBRARY_PATH=$LD_LIBRARY_PATH:/usr/local/lib64
else
  LD_LIBRARY_PATH=/usr/local/lib64
fi
export LD_LIBRARY_PATH
exec /path/to/cart5 "$@"

The list of standard system directories is kept in /etc/ld.so.conf. Recent systems allow this file to include other files; if yours contains something like include /etc/ld.so.conf.d/*.conf, create a new file called /etc/ld.so.conf.d/mala.conf containing the directories you want to add. After you change /etc/ld.so.conf or an included file, run /sbin/ldconfig for your changes to take effect (this updates a cache).

(LD_LIBRARY_PATH also applies to many other unices, including FreeBSD, NetBSD, OpenBSD, Solaris and Tru64. HP-UX has SHLIB_PATH and Mac OS X has DYLD_LIBRARY_PATH. /etc/ld.so.conf has analogs on most unices but the location and syntax differs more widely.)

If you want to avoid LD_LIBRARY_PATH, you can also do this, during linking:

gcc -o exename -L/path/to/dynamiclib/ -lnameofLib \
    -Wl,-R/path/to/dynamiclib/ sourceCode1.c ...

The -Wl,... is used to pass extra commands to the linker, and in this case, with -R you tell the linker to store this path as the "default search path" for the .so.

I keep notes of many small tips like this one, at my site:

https://www.thanassis.space/tricks.html