BCA - UNIX and Shell Programming

There is no control terminal for a daemon process. It is unable to access /dev/tty. When you run "ps -ef" and look at the tty field, you'll notice that all daemons have a? for the tty.

Most daemons are designed to endure a long time, be owned by root, and perform a meaningful function.
However, none of these things are certain to be true.

The lack of a controlling terminal is the true distinguishing feature.

A daemon is just a process that runs in the background, usually waiting for something it can handle, such as print commands in the case of a printer daemon.