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Uptime And Reboot Count Calculator

Work out uptime and reboot count instantly with clear inputs, formula shown and shareable results.

About Uptime And Reboot Count Calculator

Long uptime is often presented as a virtue but usually means unactivated kernel patches: an installed kernel does not take effect until reboot, so a 400-day uptime on a patched system means hundreds of days running vulnerable code. Reboots cost a few minutes each, which is negligible against the exposure they close.

Formula

Reboot impact

downtime = reboots x minutes per reboot; availability = 1 - downtime / period; mean uptime = period / reboots

Worked example

With the default values below, Uptime And Reboot Count Calculator returns Availability from reboots alone of 99.9880%. Change any input above and every figure here is recalculated in your browser.

Inputs used

Observation periodminimum 1 days
365 days
Reboots in the periodminimum 0
14
Minutes lost per rebootminimum 0.01 min
4.5 min
Kernel updates released in the periodminimum 0
22

Results

Availability from reboots alone
99.9880%
Mean uptime between reboots
26.1 days
Total reboot downtime
63.0 min
Kernel patch activation
8 kernel updates were installed without a reboot to activate them

Step by step

  1. 1Values used
  2. 2Reboot impact
  3. 3Availability from reboots alone= 99.9880
  4. 4Mean uptime between reboots= 26.1 days
  5. 5Total reboot downtime= 63.0 min
  6. 6Kernel patch activation= 8 kernel updates were installed without a reboot to activate them

Assumptions and limits

  • The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation or fees or charges into account.
  • Figures are rounded for display to 4 decimal places, 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

Is high uptime a good sign?

Not for security. It usually indicates deferred kernel updates. Regular planned reboots, ideally rolling across a cluster, are healthier than long uptime.

Can kernel patches apply without reboot?

Live patching exists for critical fixes on some distributions, but it covers a subset of changes. Reboots remain necessary for full kernel upgrades.

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