wiki/notebook/linux.systemd.org

systemd

• systemd at user-level
• Navigating systemd documentation
• Extra information

systemd is a big tool for a big system. Let's explore some of them from a perspective of a wannabe power user.

Among other things, it has the following list of features.

• systemd timers which can replace cron for task scheduling.
• systemd services along with the usual antics of a service manager such as managing dependencies and commands to run when killed.
• systemd transient units for quickly creating and scheduling one-off services.
• systemd unit templates is handy for managing units that have common structure, enabling to start them quickly and dynamically.
• systemd environment directives enable setting environment variables from a systemd-ful session.
• systemd-networkd is the network configuration manager in case you want to do Network configuration in Linux.
• systemd-boot is a bootloader mainly for UEFI-based systems.
• systemd-journald is the system logging service providing a structured way to manage your logs from different units.
• systemd unit hardening can help your services secure.

systemd at user-level

systemd has the ability to run at user-level empowering the user to manage their own system with their own settings. It immensely helps separating user-specific settings from the system-wide settings.

systemd looks for the units from certain paths. You can look for them from the systemd.unit.5 manual page.

To run systemd as a user instance, simply add a --user flag beforehand for systemctl and other systemd binaries, if applicable.

# See how different the output when run at user- and system-level.
systemctl --user show-units
systemctl show-units

systemctl --user show-environment
systemctl show-environment

systemctl --user start $SERVICE

Navigating systemd documentation

Because of the wide scope of the tool, it is best to know where you can find certain information. Here's an exhaustive list of the locations.

• Most sensible distributions should include the manual pages from the software. systemd has a lot of them from knowing systemd timers at systemd.timers.5, the unit formats and their locations at systemd.unit.5.
• systemd.directives.7 is an index of configuration directives including unit keys, environment variables, and command line options for systemd-related things. Also contains the related manual pages for a deeper references. ¹
• On a similar note, systemd.index.7 is an alphabetical index of the important keywords found in systemd.

Extra information

• systemd.mount units require the filename to be the mountpoint. Though, it has to be converted to what systemd accepts (e.g., systemd-escape --path $PATH).
• systemd has a few usual units such as default.target which is a target for the current environment of the user. It can be get with systemctl get-default command. More can be seen with systemd.special.7 from the manual.
• Not all units are equal as systemd treats some units specially. You can see what these specific units are and what it does with systemd.special.7 from the manual.

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How did I pass a year without knowing this?