As a daemon or daemon [ di ː mən ] (also often in the spelling Demon ) is called on a Unix or Unix-like systems, a program that runs in the background and certain services provides. User interactions find this only in an indirect way instead of, for example, via signals, pipes, and above all (network) sockets. The term daemon is also interpreted as an abbreviation of disk and execution monitor, but this is a backronym.
In Microsoft Windows, the corresponding services programs or system services are called.
Call and Operation
Typically daemons are not started by user interaction, but automatically when you switch to another runlevel or at system startup. This set daemon represents a substantial portion of the boot process, as in most Unix derivatives, the main application logic of the operating system runs in user space and thus into the daemons. Typical daemon programs are for Unix operating systems, therefore, not only server processes such as network services, e -mail servers, database servers, and print servers, but also the processes that perform the hardware configuration and monitoring, as Sounddaemons or Wechselmedienverwaltungsdaemons. Also, periodic tasks or at specified times resulting objects are realized by using daemons.
Daemons but also as normal processes in a shell can be started by a user. Then forking these processes and create in this way a process that is no longer connected to the invoking shell, and thus is a direct child process of the main process init. In practice, many daemons are designed so that they can run via command line parameter optional in both the background ( detached ) and in the foreground, that is, in the context of the shell, can remain. Often log messages are output to standard output.
To describe their daemon character, has the name of many of these programs is a mounted "d", syslogd or cupsd for example.
Alluding to a demon, the BSD Unix derivatives have made such a to the logo. The figure contains some imagery that characterizes daemons. She was chosen as the logo for this Unix derivatives, because daemons represent a key operating system component.