Connecting to a Windows Machine From Linux With Putty

1. Overview

PuTTY is a popular open-source SSH client software for Windows. However, we can also use PuTTY on a Linux machine.

In this tutorial, we explore a way to connect a Linux machine to a Windows machine using PuTTY.

2. Enable OpenSSH Server on Windows

OpenSSH is an open-source application that offers both client and server SSH utilities. Also, OpenSSH is free as an additional feature on Windows systems from version 10.

2.1. Install the OpenSSH Server

Here, we’ll install an SSH server on a Windows system. Again, we can install the OpenSSH Server from the Optional features settings on Windows. To illustrate, let’s start with the following steps on a Windows 10 system:

1. Click on the Settings icon
2. Select Apps
3. Locate the Apps & features section

We should have a link to the Optional features:

Further, let’s select Optional features and scan the list to see if the OpenSSH Server is already installed. If not, let’s do so now:

1. Select Add a feature at the top of the page
2. Search for OpenSSH Server in the search bar
3. Mark the checkbox for OpenSSH Server
4. Click Install(1) at the bottom of the screen

Once the process concludes, we can return to Optional features. Now, we should see OpenSSH Server in the list.

Alternatively, we can install the OpenSSH Server from the command line. First, let’s check if we already have the OpenSSH Server on our system. To do so, we need administrative access to PowerShell:

PS C:\> Get-WindowsCapability -Online | Where-Object Name -like 'OpenSSH*'

Name : OpenSSH.Client~~~~0.0.1.0
State : Installed

Name : OpenSSH.Server~~~~0.0.1.0
State : NotPresent

The result shows that we don’t have the OpenSSH Server on our system. Now, we’ll install the program from PowerShell with the Add-WindowsCapability command:

PS C:\> Add-WindowsCapability -Online -Name OpenSSH.Server~~~~0.0.1.0

Operation
     Running
       [ooooooooooooooooooooooooooooooooooo                                   ]

Path          :
Online        : True
RestartNeeded : False

Next, we’ll proceed to start the OpenSSH Server process and prepare it for connection.

2.2. Start the sshd Service

Following the setup of the OpenSSH Server, we can start it. sshd is the OpenSSH Server process.

To start sshd, we’ll launch PowerShell as an administrator.

First, let’s check the state of the sshd service:

PS C:\> Get-Service sshd

Status   Name               DisplayName
------   ----               -----------
Stopped  sshd               OpenSSH SSH Server

Here, we see that sshd is not running, so we’ll start it:

PS C:\> Start-Service sshd
WARNING: Waiting for service 'OpenSSH SSH Server (sshd)' to start...

Further, let’s check the status of the service:

PS C:\> Get-Service sshd

Status   Name               DisplayName
------   ----               -----------
Running  sshd               OpenSSH SSH Server

In addition, we can configure the sshd service to start on system start-up:

PS C:\> Set-Service -Name sshd -StartupType 'Automatic'

Also, the OpenSSH Server creates and enables the OpenSSH-Server-In-TCP firewall rule. This opens up port 22 for inbound SSH traffic. Of course, we can check to ensure the port is active:

PS C:\> Get-NetFirewallRule -Name *ssh*

Name                  : OpenSSH-Server-In-TCP
DisplayName           : OpenSSH SSH Server (sshd)
Description           : Inbound rule for OpenSSH SSH Server (sshd)
DisplayGroup          : OpenSSH Server
Group                 : OpenSSH Server
Enabled               : True
Profile               : Any
Platform              : {}
Direction             : Inbound
Action                : Allow
EdgeTraversalPolicy   : Block
LooseSourceMapping    : False
LocalOnlyMapping      : False
Owner                 :
PrimaryStatus         : OK
Status                : The rule was parsed successfully from the store. (65536)
EnforcementStatus     : NotApplicable
PolicyStoreSource     : PersistentStore
PolicyStoreSourceType : Local

To clarify, the output shows that the firewall allows for inbound SSH traffic via Action:Allow and Direction:Inbound. If it’s missing, we can always add it:

PS C:\> New-NetFirewallRule -Name 'OpenSSH-Server-In-TCP' -DisplayName 'OpenSSH Server (sshd)' -Enabled True -Direction Inbound -Protocol TCP -Action Allow -LocalPort 22

Next, let’s install and set up PuTTY on Linux.

3. PuTTY on Linux

Initially, we set up an SSH server on the host Windows machine. Now, we’ll install the PuTTY SSH client on a Linux system.

3.1. Install PuTTY

Notably, under Ubuntu, PuTTY is available in the Universe repository. It’s usually enabled by default, but we can also enable the repository manually:

$ sudo add-apt-repository universe

Then, let’s update our Linux system package repository:

$ sudo apt-get update

Next, let’s install PuTTY:

$ sudo apt-get install -y putty
Reading package lists... Done
Building dependency tree 
Reading state information... Done
The following additional packages will be installed:
putty-tools
...

Here, the -y flag confirms any prompts during the process. In addition, the command installs PuTTY with putty-tools, which includes several utilities:

• pscp for copying files through the Secure Copy Protocol (SCP)
• psftp for managing files using SSH File Transfer Protocol (SFTP)
• puttygen for generating RSA and DSA keys

Lastly, we can verify the process is complete by checking the version we installed:

$ putty --version
PuTTY: Release 0.73
Build platform: 64-bit Unix (GTK + X11)
Compiler: gcc 9.3.0
Compiled against GTK version 3.24.14
Source commit: 745ed3ad3beaf52fc623827e770b3a068b238dd5

Next, we’ll create the public authentication key.

3.2. Generate Public Key

PuTTY allows for public key authentication using the puttygen tool. Importantly, puttygen saves the key in a .ppk key file format.

Let’s use puttygen to enable public key authentication:

$ puttygen -t rsa -b 2048 -o pubkey.ppk
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
++++++++++++++++++++++++++++++++
+++++
Enter passphrase to save key: 
Re-enter passphrase to verify: 

Here are the flags we used in the command:

• -t specifies the key type
• -b indicates the size of the key in bits
• -o defines the output file for the key

Notably, we can leave the passphrase empty. To do so, we just press Enter on passphrase prompts. Then, to get the public key, we just use puttygen again:

$ puttygen -L pubkey.ppk

Lastly, we’ll copy the public key to the Users\USERNAME\.ssh\authorized_keys file on the server. Of course, if the .ssh folder and the authorized_keys file do not already exist, we can create them.

Next, let’s establish an SSH link from our Linux machine to the Windows system using PuTTY.

4. Establish SSH Connection

Finally, having set up both the SSH client and server, let’s proceed to link to our server using PuTTY.

Since the initial steps for setting up the OpenSSH Server on Windows, our server is already listening for a connection. Now, let’s run PuTTY from the Linux command line:

$ putty
...

This command opens the PuTTY Configuration window:

Further, to connect to the host system:

• Enter the hostname or IP address of our host Windows machine in the Host Name box
• Select SSH as the Connection type

Then, we’ll bring on our security key for authentication:

• Navigate to Connection > SSH > Auth in the PuTTY menu
• Click Browse and select the key file
• Click Open

On clicking Open, the PuTTY Security Alert pops up. We’ll click Accept to continue the connection:

Following the security alert, we’ll provide our login credentials for authentication:

Now, we’ve successfully set up an SSH link to our host machine:

Lastly, we can type exit and press Enter to quit the session.

5. Conclusion

In summary, we’ve seen how to connect a Linux machine to an OpenSSH server on a Windows machine using PuTTY. Also, we created a public security key for a secure SSH connection.