Service Restart Delay Calculator
Calculate cumulative restart delay for a systemd service using exponential backoff.
About Service Restart Delay Calculator
systemd's crash-loop protection combines three settings: RestartSec (delay before each restart attempt), StartLimitBurst (max start attempts allowed) and StartLimitIntervalSec (the rolling time window StartLimitBurst is measured against) — if a unit is (re)started more than StartLimitBurst times within StartLimitIntervalSec, systemd marks it failed and stops auto-restarting until the window ages out. This calculator checks whether RestartSec's pacing would let the full burst count actually occur within the configured interval, or whether the interval resets first (making the burst limit effectively unreachable under pure RestartSec-paced restarts alone) — important for correctly tuning crash-loop protection rather than assuming StartLimitBurst always triggers as expected.
Formula
Time to exhaust the restart burst
time_to_exhaust_burst = (StartLimitBurst − 1) × RestartSec
- B
- StartLimitBurst
- R
- RestartSec
Worked example
With the default values below, Service Restart Delay Calculator returns Max Restarts Within Interval of 5. Change any input above and every figure here is recalculated in your browser.
Inputs used
- RestartSec (seconds between restart attempts)minimum 0
- 5
- StartLimitBurst (max starts allowed)minimum 1
- 5
- StartLimitIntervalSec (rate-limit window, seconds)minimum 1
- 60
Results
- Max Restarts Within Interval
- 5
- Status
- All 5 allowed restarts can occur within the 60s window (taking 20s) — after that, systemd enters the failed state and stops restarting until the interval resets.
- Time to Exhaust Full Burst (s)
- 20.0
- Burst Limit Reachable Within Interval?
- true
Step by step
- 1Values used
- 2Time to exhaust the restart burst
- 3Max Restarts Within Interval= 5
- 4Status= All 5 allowed restarts can occur within the 60s window (taking 20s) — after that, systemd enters the failed state and stops restarting until the interval resets.
- 5Time to Exhaust Full Burst (s)= 20.0
- 6Burst Limit Reachable Within Interval?= Yes
Assumptions and limits
- The result is derived only from the 3 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
- Figures are rounded for display to 1 decimal place, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Frequently Asked Questions
What happens when a systemd service exceeds StartLimitBurst?
The unit enters the 'failed' state (visible via `systemctl status`, showing a start-limit-hit condition) and systemd stops attempting further automatic restarts, even if Restart=always is set — you must manually run `systemctl reset-failed <unit>` (and fix the underlying issue) before it will resume normal restart behavior.
Why might increasing RestartSec make crash-loop protection less effective?
If RestartSec is large enough that the time to reach StartLimitBurst restarts exceeds StartLimitIntervalSec, the interval window rolls forward and resets the count before the burst limit is ever reached — meaning the service can restart-loop indefinitely at that slower pace without ever tripping the 'failed' safeguard, which may or may not be the intended behavior.
How do I tune these settings for a service that occasionally needs a few retries but shouldn't loop forever?
A common pattern is a short RestartSec (a few seconds, for fast recovery from transient failures) paired with a StartLimitBurst/StartLimitIntervalSec combination sized so genuine crash loops trip the limit within a reasonable time (e.g. burst=5 within intervalSec=60), giving quick recovery from blips while still catching persistent crash loops.