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epinheiro
Staff
epinheiro
Staff
August 29, 2025

Troubleshooting Tip: High CPU usage of linkmtd daemon when link-monitor or fail-detect is enabled

  • August 29, 2025
  • 0 replies
  • 1276 views
Description This article describes an issue where the 'linkmtd' daemon consumes high CPU when FortiGate devices process large amounts of traffic with link-monitor or fail-detect enabled.
Scope

Platforms: FortiGate 3000F, FortiGate 3001F, FortiGate 80F, FortiGate 4801F

FortiOS versions: 7.2.9 GA, 7.4.5, 7.4.8 GA, 7.4.9, 7.6.4, 7.6.5, 8.0.0
Solution

Symptoms: High CPU utilization of the 'linkmtd' daemon.

 

Cause: Under high traffic conditions, the 'linkmtd' daemon performs unnecessary session dumps and system calls during link-monitor or fail-detect operations, resulting in excessive CPU usage.

 

Workarounds:

  • Remove the link-monitor configuration.
  • Remove the fail-detect configuration.

Fixed versions:

  • FortiOS 7.4.9 build 2813
  • FortiOS 7.6.4 build 3592
  • FortiOS 8.0.0 build 0045

Resolution:

A validation check was introduced to determine whether a session dump is required before executing CPU-intensive system calls, reducing CPU consumption of the 'linkmtd' daemon.

 

Recommendation:

Always confirm the recommended FortiOS build by referring to the article Technical Tip: Recommended Release for FortiOS.
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