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Why do I have slow SSH connections?

Troubleshooting


Problem

Why do I have slow SSH connections?

Resolving The Problem

Why do I have slow SSH connections?

By default, the OpenSSH daemon is configured to enable X11 forwarding. This can sometimes slow down connecting to nodes. You can disable forwarding by using the -x option when connecting to a node to skip X11 forwarding, e.g. "ssh -x compute-0-1".

This can also be disabled permanently by editing the /etc/ssh/ssh_config file and changing the line ForwardX11 Yes and setting this to No. Note that this change will apply to all users.

If a single user would like to disable the X11 forwarding, he can create/edit $HOME/.ssh/config file by adding ForwardX11 no, e.g.
# touch .ssh/config
# chmod 600 .ssh/config
# echo "ForwardX11 no" > .ssh/config

An SSH connection from one node to another may be slow in setting up. This is usually because of a name resolution failure, and subsequent timeout. This can occur if the frontend was installed with an invalid DNS server.

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Document Information

Modified date:
09 September 2018

UID

isg3T1014136

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