Monthly Archives: November 2016

SSH from PowerShell

I’ve been playing with more non Microsoft technologies recently and even have a few Linux VMs running here and there. In the process I’ve learned a lot about interacting between the two worlds/environments using technologies like SSH and even running the Powershell Alpha previews on my Linux VMs. Then I got ‘bored’ and looked for a way to programmatically interact with my VMs (for monitoring) and discovered the open source project SSH.Net which I now have incorporated into even QuickMon. Then I got even more bored and started looking for a way to use SSH from Powershell and came across the SSH-Sessions module which incidentally also use SSH.Net to give Powershell a way to call/connect using SSH.

No PassPhrase

This all works nicely except… SSH-Sessions had one shortcoming.. which I just had to fix. The creator(s) of this module implements a way to specify a key file when connecting to an SSH server but does not provide a way to specify the ‘PassPhrase’ at all! WHY?

Any way, I knew the SSH.Net library does support it since I actually make use of this functionality in QuickMon. Then I started digging inside the SSH-Session script files and made a few adjustments…

Fix

To enable PassPhrase functionality I simply had to add the following code in the ‘New-SshSession’ function:

Change the function header to:

function New-SshSession {
    param([Parameter(Mandatory=$true)][string[]] $ComputerName,
          [Parameter(Mandatory=$true)][string]   $Username,
          [string] $KeyFile = '',
          [string] $PassPhrase = 'blankPassphrase',
          [string] $Password = 'SvendsenTechDefault', # I guess allowing for a blank password is "wise"...          
          [int] $Port = 22,
          [switch] $Quiet
    )

and then inside the function:

if ($KeyFile -ne '') {
        if (-not $Quiet) {
            "Key file specified. Will override password. Trying to read key file..."
        }
        if ($PassPhrase -eq 'blankPassphrase') {
            $SecurePassPhrase = Read-Host -AsSecureString "key provided. Please enter pass phrase for $KeyFile"
            $PassPhrase = ConvertFrom-SecureToPlain $SecurePassPhrase
        }
        if (Test-Path -PathType Leaf -Path $Keyfile) {
            $Key = New-Object Renci.SshNet.PrivateKeyFile( $Keyfile, $PassPhrase ) -ErrorAction Stop
        }
        else {
            "Specified keyfile does not exist: '$KeyFile'."
            return
        }   
    }

Example

And with the you can now use the module to connect to SSH using a Key file that has a PassPhrase. If you don’t specify the PassPhrase the script will prompt you for one. If you actually don’t have a PassPhrase at all then pass an empty string as the value of PassPhrase (not tested but it should work).

Import-Module SSH-Sessions
New-SshSession -Computer mySSHServer -Username me  -KeyFile 'c:\mykeys\mykey.key' -PassPhrase 'somePhrase'
Invoke-SshCommand  -ComputerName mySSHServer -Command "cat /proc/cpuinfo | grep processor" -Quiet
Remove-SshSession -RemoveAll -Quiet

How to install Powershell on Ubuntu 16.10

I recently tried installing the latest Alpha of Powershell (Alpha 12) on the newly released Ubuntu 16.10 and discovered that the install failed because of a dependency on the library libicu55 which has been replaced in the new version of Ubuntu (libicu57). Actually, the whole .Net Core install fails because of this.

Fortunately this is easy to fix by manually installing the old library from http://cz.archive.ubuntu.com/ubuntu/pool/main/i/icu/libicu55_55.1-7_amd64.deb

Then you can download the latest Powershell version (Alpha 12 as of this writing) from https://github.com/PowerShell/PowerShell/releases

Hopefully the creators of the Powershell packages will release an updated version that is natively compatible with Ubuntu16.10.