Last Updated: 2024-04-25

Note: This is unix specific

exec

• can used to replace the current process with a completely different program
• discards process memory and a whole new executable is loaded
• while retaining kernel state (e.g. open files, environment variables, user, working directory)
• because it replaces the current process, it does not generate a new pid

vs. fork

• copy of current process
• retains process memory
• also retains ("inherits") kernel state
• brand new pid

Usage

Typically we fork a running program first, then exec the forked child process to run a different program.

Usually we modify child process state (e.g. time zone, working directory, file handlers) after forking but before execing

Resources

• https://unix.stackexchange.com/questions/231766/fork-and-exec-confusion#:~:text=Incidentally%2C%20exec%20does%20not%20generate,the%20PID%20remains%20the%20same.
• https://www.rubytapas.com/2017/10/09/episode-500-subprocesses-11-fork-and-exec/