Summary

When Bamboo kills git command it leaves ssh process untouched. It will remain executed until JVM shutdown

Details

Create plan with large repository checkout task. Use SSH key for repository authentication and native git as capability. Set command timeout for 1 minute in repository settings
Start build
See process list

ps axvf

java
  \-git
      \-ssh -o ...

Wait for 1 minute when checkout is timed out and Bamboo interrupts plan
See process list

ps axvf

java
  \-ssh -o ...

Workaround

Manually kill ssh processes which are not children of git process