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Hands-on Lab·Linux Foundation Certified System Administrator

systemd units, services and targets

systemctl is the same program on both distributions and it is a quarter of the exam's biggest domain. The marks are in the distinctions: active is not enabled, disabled is not masked, and a unit with no [Install] section cannot be enabled at all. This guide separates them with output rather than definitions.

Operations Deployment Guide 13 of 38 Intermediate

systemd 257 on RHEL 10; the lab's Ubuntu hosts run 259. Nothing on this page differs between the two versions. Unit names do differ between the families - sshd.service against ssh.service.

Both families. The RHEL transcript came first, during an outage that took both Ubuntu hosts offline; the Ubuntu half was captured afterwards and is the last step of each page, because Ubuntu is what LFCS is most likely to sit you in front of.
Server NameIP AddressOSRolesCPURAMHDD
LFCS-A01192.168.0.70Ubuntu 26.04 LTSPrimary host - most guides run only here2 Core4 GB50 GB
LFCS-C01192.168.0.72AlmaLinux 10.2The other distribution - dnf, firewalld and NetworkManager2 Core4 GB50 GB

This guide includes

Use this for a quarter of the exam. This matters because enable is only a symlink and mask is stronger than disable - a disabled unit still starts the moment something asks for it.

Before you start

  1. What is running, and what has failed

  2. Three questions that look like one

  3. What a unit file actually says

  4. The dependency tree, in both directions

  5. Targets, which replaced runlevels

  6. Enable is a symlink, and nothing more

  7. A unit with no [Install] section cannot be enabled

  8. Disable is not mask

  9. Masking, which is stronger - and which can fail

  10. The same units on Ubuntu, under different names

Official sources

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