What are the daemons?

A daemon is a process that runs in the background and is not attached to a controlling terminal.

Typically, daemons are started at system boot, run as root or another dedicated user (for example apache or postfix), and perform system-level tasks. Traditionally many daemon program names end with the letter d (for example crond and sshd), but this is a convention rather than a requirement.

Daemons commonly have two requirements:

• they should run as a child of init (or the system's init replacement),

• they must not be attached to a terminal.