First of all, every time you execute a command, you shell will fork a new process, regardless of whether you run it with
& or not.
& only means you're running it in the background.
Note this is not very accurate. Some commands, like
cd are shell functions and will usually not fork a new process.
type cmd will usually tell you whether
cmd is an external command or a shell function.
type type tells you that
type itself is a shell function.
nohup is something different. It tells the new process to ignore
SIGHUP. It is the signal sent by the kernel when the parent shell is closed.
To answer your question do the following:
emacs & (by default should run in a separate X window).
- on the parent shell, run
You'll notice that the
emacs window is killed, despite running in the background. This is the default behavior and
nohup is used precisely to modify that.
Running a job in the background (with
bg, I bet other shells have other syntaxes as well) is a shell feature, stemming from the ability of modern systems to multitask. Instead of forking a new shell instance for every program you want to launch, modern shells (
ksh, ...) will have the ability to manage a list of programs (or jobs). Only one of them at a time can be at the foreground, meaning it gets the shell focus. I wish someone could expand more on the differences between a process running in the foreground and one in the background (the main one being acess to
In any case, this does not affect the way the child process reacts to