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Trace the Boot Critical Path with systemd-analyze critical-chain

critical-chain prints the chain of units that most delayed reaching the default target, with @ and + markers for start time and duration.

LinuxbootperformancesystemdLow risk
Run `systemd-analyze critical-chain` to show the dependency chain that determines boot completion time; add a unit name to trace the chain for a specific service.

01Command

Command
$ systemd-analyze critical-chain

02What it does

Unlike blame, which measures each unit in isolation, critical-chain shows the serialized chain of units that actually delayed the default target — marked with @ (time the unit became active) and + (how long it took). Units that ran in parallel are irrelevant to boot time even if individually slow. Use `systemd-analyze critical-chain <unit>` to analyze a single service's dependency path.

03Risk

RiskLow risk
Requirementssystemd-based distribution.

04Undo

✓No undo needed — this command does not change persistent state.

05Sources

  • systemd-analyze(1)
    Ubuntu Manpages · technical · 2026-09-17
    Evidence: critical-chain [UNIT...] prints a tree of the time-critical chain of units, showing when each became active and how long after the previous one.

Last verified: 2026-09-17 · Category: System & Settings

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