How to prevent a Linux program from running more than once?

How to prevent a Linux program from running more than once?

c++ c linux unix executable

unix

Using dlopen() on an executable

unix executable dlopen

unix

Creating an a.out executable from scratch

c unix compiler-construction executable machine-code

unix

Is a core dump executable by itself?

linux unix executable coredump executable-format

unix

UNIX cc executable location

c unix executable cc

unix

Is chaining interpreters via shebang lines portable?

linux shell unix posix executable

unix

Python: simple example trying to create a unix command-line executable - why won't it work?

python unix executable

unix