Targets — systemd's Answer to Runlevels

systemd1-4 defined a target as a synchronization point without going further. This chapter goes further — and resolves grub1-4's own unexplained systemd.unit=rescue.target kernel parameter along the way.

What a Target Actually Is, Formally

systemd1-4 established that a target doesn't "do" anything itself. Formally: a target unit is a named grouping of other units — often implemented as essentially an empty unit that other units Want=/Require=/order themselves relative to. "Reaching a target" means every unit that target itself requires or wants, directly or transitively, has actually been started.

The Common Targets, Mapped to Legacy Runlevels

graphical.target itself Wants=multi-user.target, since graphical mode is a strict superset — everything multi-user mode provides, plus a display manager on top.

The Default Target

Which target boots by default is determined by a symlink — /etc/systemd/system/default.target pointing at the chosen target — genuinely similar in spirit to systemd1-3's own WantedBy= symlink mechanism, just applied to the top-level boot target rather than an individual service. A headless server typically defaults to multi-user.target; a desktop distro typically defaults to graphical.target.

systemctl isolate — Switching Targets Live

Run on a live graphical system, this stops everything not required by multi-user.target — the display manager included — and starts anything multi-user.target requires that wasn't already running. A genuine live runlevel-style switch, no reboot required. A real, practical use: temporarily dropping out of a graphical environment to troubleshoot a display/GPU driver issue, then isolating back to graphical.target once fixed.

Direct Legacy Comparison

systemd1-1's own System V material named telinit 3 as the legacy way to switch runlevels live. That maps directly to systemctl isolate multi-user.target — the same real-world action, but a genuinely different, more expressive mechanism underneath: an actual dependency-resolution operation, not a legacy numbered switch with no explicit relationship to what it starts or stops.

Resolving grub1-4's Own rescue.target

grub1-4 taught appending systemd.unit=rescue.target at the GRUB menu to reach a recovery shell, without explaining what that parameter actually meant. Now it's clear: this tells systemd to boot straight to this target instead of the normal default, bypassing graphical.target/multi-user.target's own much larger set of Wants=/Requires= dependencies entirely, landing in a genuinely minimal environment with far fewer units started — exactly why it's usable for recovery even when something elsewhere in the normal boot chain is broken.

Hands-On Exercises