An overview of Systemd was provided in Chapter 1, CoreOS Overview. Systemd is the init system used by CoreOS and is always on by default. In this section, we will walk through some of the Systemd internals.

Unit types

Units describe a particular task along with its dependencies and the execution order. Some units are started on the CoreOS system by default. CoreOS users can also start their own units. System-started units are at /usr/lib64/systemd/system and user-started units are at /etc/systemd/system.

The following are some of the common unit types:

  • Service unit: This is used to start a particular daemon or process. Examples are sshd.service and docker.service. The sshd.service unit starts the SSH service, and docker.service starts the ...

Get Mastering CoreOS now with O’Reilly online learning.

O’Reilly members experience live online training, plus books, videos, and digital content from 200+ publishers.