I ran into a situation with a project where I needed to build two separate programs to work together. The first being a server, and the second being an on-going client-facing process. The server is designed to kick off any number of instances of the on-going process. Before having written any code to have the server run the on-going processes as children, I had intended the child processes to be independent of the server. That is, if the server went down, the child processes would still function. They would store requests in a queue and periodically attempt to reconnect to the server. Once the connection was re-established, everything would go back to normal. It turned out that Unix processes don’t quite work like I had expected.
In reality, when a process spawns another process, it is called a “child”; the original is called the “parent”. As long as the parent process has not exited, the child will continue to run. If for some reason the parent goes down, so does the child. That is, unless the child is considered “detached”. A child process is detached when it no longer has a parent (I believe that technically, parent-less children are owned by an
init process). Thus, you can have a parent process spawn a detached child and immediately exit, which will leave the child process all alone.