What is the difference between static and dynamic linking?

Static linking copies all library code into the executable at build time; dynamic linking leaves it in shared .so files that are resolved at load time.

Static linking:

# Everything included in executable
$ gcc -static -o prog main.c
$ ldd prog
    not a dynamic executable

Dynamic linking (default):

$ gcc -o prog main.c
$ ldd prog
    linux-vdso.so.1
    libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6
    /lib64/ld-linux-x86-64.so.2

Tip: Most modern programs use dynamic linking for smaller binaries and shared library updates, but static linking is useful for maximum portability.

Go deeper:

• Static library (Wikipedia) — copying library code in at build time, and its trade-offs.
• Dynamic linker (Wikipedia) — the load-time alternative that keeps library code in shared .so files.