Why does ssh fail with the messages "Connection closed by xxx.xxx.xxx.xxx"?

Solution Verified - Updated -

Environment

  • Red Hat Enterprise Linux 5
  • Red Hat Enterprise Linux 6

Issue

  • Why does ssh fail with the messages "Connection closed by xxx.xxx.xxx.xxx"?

Resolution

Check LoginGraceTime in /etc/ssh/sshd_config and whether ssh server is very slow. If ssh server has dns access problem, it may take dozens of seconds to wait until DNS PTR queries time out.

From the man SSHD_CONFIG(5):

LoginGraceTime
  The server disconnects after this time if the user has not successfully logged in.  
  If the value is 0, there is no time limit.  The default is 120 seconds.

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