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Why is my ssh connection from one compute node to another slow?

Troubleshooting


Problem

Why is my ssh connection from one compute node to another slow?

Resolving The Problem

Why is my ssh connection from one compute node to another slow?

Symptom: ssh from one compute node to another is slow in establishing a connection.

To test if this is the cause, perform the following:

1. Log in to a compute node and establish an ssh connection with another compute node using its host name:

# ssh another_compute_node_hostname

Take note of the time required.

2. Log out of the other compute node and try to establish a connection using its IP address:

# ssh another_compute_node_ipaddress

If the result is dramatically faster, the problem is with name resolution.

Explanation: The cluster may be trying to use a non-existent domain or DNS server.

To verify this problem is with name resolution edit the /etc/resolv.conf file on a compute node. Change the search line to only include the private domain.

Establish an ssh connection to another compute node. It should respond faster.

Solution: Fix this problem using any one of the following:

  • Update the front end’s /etc/resolv.conf file to use a real DNS server.
  • Update the database and set the PublicDNSDomain in the app_globals table to be blank.  Remove the Kickstart cache by removing the file(s):  /home/install/sbin/cache/ks.cache.*.   Then reinstall the compute nodes.
  • As a temporary fix, change the search parameter in the /etc/resolv.conf of all the compute nodes.

 

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Document Information

More support for:
IBM Spectrum Cluster Foundation

Software version:
4.4.0

Document number:
702015

Modified date:
09 September 2018

UID

isg3T1014117