5

I am currently trying to make a control panel-like program for my Linux server using Visual Basic and SSH.NET. Right now, I want to make the Linux machine reboot when I press a button.

Here is what I have so far:

Dim connInfo As New Renci.SshNet.PasswordConnectionInfo("IP", "USERNAME", "PASSWORD")
Dim sshClient As New Renci.SshNet.SshClient(connInfo)
Dim cmd As Renci.SshNet.SshCommand

Private Sub MaterialFlatButton1_Click(sender As Object, e As EventArgs) Handles MaterialFlatButton1.Click
    Using sshClient
        sshClient.Connect()
        cmd = sshClient.RunCommand("reboot")
        sshClient.Disconnect()
    End Using
End Sub

When I press the button, the error I get is:

An unhandled exception of type 'Renci.SshNet.Common.SshConnectionException' occurred in Renci.SshNet.dll

Additional information: An established connection was aborted by the software in your host machine.

Is there anything I would need to change with my code?

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3 Answers 3

Reset to default
7

If you are the server administrator, there is the option of limiting the Key Exchange Algorithms to diffie-hellman-group1-sha1. It is important to notice that this algorithm is not considered safe anymore, but Open SSH supports it.

To do that, go to your linux server and edit the file

/etc/ssh/sshd_config

Add the lines (somewhere in the middle of the file)

# Disable all Kex Algorithms but the one defined below (so Renci SSH.NET 2013 works)
KexAlgorithms diffie-hellman-group1-sha1

Restart ssh:

sudo service ssh stop
sudo service ssh start

Now SSH.NET will work, but to connect to the server via ssh (terminal), you should define the protocol on you client config file:

Edit the file (I'm using ssh on cygwin, other clients are beyond my knowledge)

~/.ssh/config

Add the line

KexAlgorithms +diffie-hellman-group1-sha1

Just to conclude, I ended up not using this solution because the latest filezilla does not connects with the server, and I have a user using it to upload files.

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5

I encountered this same problem myself. tl;dr: upgrade to the beta version of SSH.NET:

Install-Package SSH.NET -Pre

To Elaborate Further

If you examine your logs on your linux server immediately after your unsuccessful attempt to connect:

grep 'sshd' /var/log/auth.log

You'll probably see a line like this:

sshd[2467]: fatal: mm_answer_moduli: bad parameters: 2048 2048 1024

Recent versions of ssh server has become more strict, and the current (stable) version of SSH.NET does not support this. More specifically, it has become more strict by requiring a larger key size than 1024. You can see the bug report on codeplex. And here's a person experiencing a similar problem for whom upgrading also worked.

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The beta version of SSH.NET appear to have memory leaks (I had problems with it today), use with caution. There's an open pull request addressing the problem: github.com/sshnet/SSH.NET/pull/7/files/…
@MarcosBrigante, thanks for bringing that to the community's attention!
I'm using 2016 version now and still facing the same issue.
0

The RunCommand method expects a response from the connected device. Running the reboot, poweroff, or shutdown commands will not allow for a response from the device and causes an SshConnectionException to occur.

I wrapped this command in a try/catch as this exception is expected. Here's an example in C#:

try
{
    sshClient.RunCommand("reboot");
}
catch (SshConnectionException exception)
{
    // do something
}
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