SSH connection Slow

Because many people reflect the company test environment Server SSH connection is very slow, to troubleshoot the ping does not drop packets, that is the problem of system configuration. Search on the Internet, the results are very practical.

First, the cause of the investigation

Before testing :

Ssh-v 192.168.1.138

Then there will be a lot of bugs

For example:

Debug1:next Authentication Method:gssapi-keyex

Debug1:no Valid Key Exchange context

Debug1:next Authentication Method:gssapi-with-mic

Debug1:unspecified GSS failure. Minor code may provide more information

Credentials cache file '/tmp/krb5cc_0 ' not found

Debug1:unspecified GSS failure. Minor code may provide more information

Credentials cache file '/tmp/krb5cc_0 ' not found

Debug1:unspecified GSS failure. Minor code may provide more information

Debug1:unspecified GSS failure. Minor code may provide more information

Credentials cache file '/tmp/krb5cc_0 ' not found

Debug1:next Authentication Method:publickey

Debug1:trying private key:/root/.ssh/identity

Check the connection time:

Time ssh [email protected] Exit

Real0m4.785s

User0m0.014s

SYS0m0.011s

Second, configuration optimization

1. Turn off DNS reverse resolution

In Linux, the SSHD service is turned on by default for DNS resolution. It consumes time, so it needs to be closed.

Vim/etc/ssh/sshd_config

Usedns No

Although it is commented out, the default is yes.

Time ssh [email protected] Exit

Real0m3.978s

User0m0.016s

SYS0m0.010s

See the actual connection time significantly reduced a lot. The explanation played a role!

2. Turn off authentication for server

During the authority process, gssapi-with-mic can be a big problem, so shutting down the GSSAPI increases the speed.

Vim/etc/ssh/sshd_config

Gssapiauthentication No

Save launch

Time ssh [email protected] Exit

Real 0m3.832s

User 0m0.011s

SYS 0m0.004s

The time was significantly reduced by a lot. Basically, it can be used normally.

This article from "The Dark before Dawn" blog, declined reprint!

SSH connection Slow