Mastering Embedded Linux Programming - Second Edition

Daemons

We have encountered daemons in several places already. A daemon is a process that runs in the background, owned by the init process and not connected to a controlling Terminal. The steps to create a daemon are as follows:

1. Call fork to create a new process, after which the parent should exit, thus creating an orphan which will be re-parented to init.
2. The child process calls setsid(2), creating a new session and process group of which it is the sole member. The exact details do not matter here; you can simply consider this a way of isolating the process from any controlling terminal.
3. Change the working directory to the root directory.
4. Close all file descriptors and redirect stdin, stdout, and stderr (descriptors 0, 1, and 2) to /dev/null ...