Targets and services are types of systemd unit, a topic which will be covered later in this chapter. Different systemd targets are configured to automatically launch different collections of services, depending on the functionality that is to be provided by that target. The sshd service, for example, is the background process (also referred to as a daemon) that provides secure shell access to the system. 1.2 Understanding Ubuntu systemd ServicesĪ service is essentially a process, typically running in the background, that provides specific functionality. For those familiar with previous Ubuntu versions, systemd targets are the replacement for the older runlevel system. ![]() Having identified the default target, it proceeds to start the systemd units associated with that target so that the system boots with all the necessary processes running. A desktop system, for example, will most likely be configured to boot using the graphical user interface target, while a cloud-based server system would be more likely to boot to the multi-user target level.ĭuring the boot sequence, a process named systemd looks in the /etc/systemd/system folder to find the default target setting. The target to which a system will boot by default is configured by the system administrator based on the purpose for which the system is being used. Ubuntu can be configured to boot into one of a number of states (referred to as targets), each of which is designed to provide a specific level of operating system functionality. ![]() The goal of this chapter, therefore, is to provide a basic overview of the different systemd units supported by Ubuntu combined with an overview of how to configure the many services that run in the background of a running Linux system. In order to gain proficiency in Ubuntu system administration it is important to understand the concepts of systemd units with a particular emphasis on two specific types known as targets and services.
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