What Is Daemon (Computing)?

Daemon is a term popularly used in computing especially in operating systems. Daemon is a process which is runs in the background in order to fulfill different tasks. The daemon term is popularly used in Unix, Linux, and BSD systems in order to define services. The Microsoft Windows counterpart of the daemon is service.

The name daemon first used by the programmer of the MIT Project MAC. It is very interesting that the daemon comes from mythology where it is an imaginary being operating background.

Naming Daemon

In Unix, Linux and BSD there are different types of daemons used for different tasks and serving resources. these daemons use names with ending with a d as a process to depict it is a daemon, not a regular process.

Manage Daemon

Daemons can be managed using commands like systemctl , service , /etc/init.d scripts and commands etc. But today the systemctl command is the defacto standard to manage daemons. Existing daemons can be listed with the following systemctl command.

$ systemctl

A specific daemon and its current status can be listed like below. In the following example we will list the SSH daemon which is named as ssh as a services but the process it named as sshd.

$ systemctl status ssh

We can see from the Man PID line which is sshd which is short form of the SSH Daemon .

A daemon can be stopped with the systemctl stop command like below. But this operation generally requires root privileges which can be provided with the sudo command like below.

$ sudo systemctl stop ssh

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