Parent page: Internet and Networking >> SSH

• You can configure the SSH server to use PowerShell as the default shell and to load a profile through SSH. See the SSH documentation for more information. Prior to PowerShell 7.1, remoting over SSH did not support second-hop remote sessions.
• The SSH config file allows you to create different profiles for different host configurations. There is no limit to such profiles and you may add as many as possible. So, if you connect to multiple remote systems via SSH, creating SSH profiles will be a good move to save your time. Let me show you how to use it.

Nov 22, 2020 The rules are as follows to create an ssh config file: You need to edit /.ssh/config with a text editor such as vi. One config parameter per line is allowed in the configuration file with the parameter name followed by its value or values.

Once you have installed an OpenSSH server,

you will need to configure it by editing the sshd_config file in the /etc/ssh directory.

First, make a backup of your sshd_config file by copying it to your home directory, or by making a read-only copy in /etc/ssh by doing:

Creating a read-only backup in /etc/ssh means you'll always be able to find a known-good configuration when you need it.

Once you've backed up your sshd_config file, you can make changes with any text editor, for example;

runs the standard text editor in Ubuntu 12.04 or more recent. For older versions replace 'sudo' with 'gksudo'. Once you've made your changes (see the suggestions in the rest of this page), you can apply them by saving the file then doing:

If you get the error, 'Unable to connect to Upstart', restart ssh with the following:

Configuring OpenSSH means striking a balance between security and ease-of-use. Ubuntu's default configuration tries to be as secure as possible without making it impossible to use in common use cases. This page discusses some changes you can make, and how they affect the balance between security and ease-of-use. When reading each section, you should decide what balance is right for your specific situation.

Because a lot of people with SSH servers use weak passwords, many online attackers will look for an SSH server, then start guessing passwords at random. An attacker can try thousands of passwords in an hour, and guess even the strongest password given enough time. The recommended solution is to use SSH keys instead of passwords. To be as hard to guess as a normal SSH key, a password would have to contain 634 random letters and numbers. If you'll always be able to log in to your computer with an SSH key, you should disable password authentication altogether.

If you disable password authentication, it will only be possible to connect from computers you have specifically approved. This massively improves your security, but makes it impossible for you to connect to your own computer from a friend's PC without pre-approving the PC, or from your own laptop when you accidentally delete your key.

It's recommended to disable password authentication unless you have a specific reason not to.

To disable password authentication, look for the following line in your sshd_config file:

replace it with a line that looks like this:

Once you have saved the file and restarted your SSH server, you shouldn't even be asked for a password when you log in.

By default, you can tunnel network connections through an SSH session. For example, you could connect over the Internet to your PC, tunnel a remote desktop connection, and access your desktop. This is known as 'port forwarding'.

By default, you can also tunnel specific graphical applications through an SSH session. For example, you could connect over the Internet to your PC and run nautilus 'file://$HOME' to see your PC's home folder. This is known as 'X11 forwarding'.

While both of these are very useful, they also give more options to an attacker who has already guessed your password. Disabling these options gives you a little security, but not as much as you'd think. With access to a normal shell, a resourceful attacker can replicate both of these techniques and a specially-modified SSH client.

It's only recommended to disable forwarding if you also use SSH keys with specified commands.

To disable forwarding, look for the following lines in your sshd_config:

and replace them with:

If either of the above lines don't exist, just add the replacement to the bottom of the file. You can disable each of these independently if you prefer.

You can explicitly allow or deny access for certain users or groups. For example, if you have a family PC where most people have weak passwords, you might want to allow SSH access just for yourself.

Allowing or denying SSH access for specific users can significantly improve your security if users with poor security practices don't need SSH access.

It's recommended to specify which accounts can use SSH if only a few users want (not) to use SSH.

To allow only the users Fred and Wilma to connect to your computer, add the following line to the bottom of the sshd_config file:

To allow everyone except the users Dino and Pebbles to connect to your computer, add the following line to the bottom of the sshd_config file:

It's possible to create very complex rules about who can use SSH - you can allow or deny specific groups of users, or users whose names match a specific pattern, or who are logging in from a specific location. For more details about how to create complex rules, see the sshd_config man page

It's possible to limit the rate at which one IP address can establish new SSH connections by configuring the uncomplicated firewall (ufw). If an IP address is tries to connect more than 10 times in 30 seconds, all the following attempts will fail since the connections will be DROPped. The rule is added to the firewall by running a single command:

On a single-user or low-powered system, such as a laptop, the number of total simultaneous pending (not yet authorized) login connections to the system can also be limited. This example will allow two pending connections. Between the third and tenth connection the system will start randomly dropping connections from 30% up to 100% at the tenth simultaneous connection. This should be set in sshd_config.

In a multi-user or server environment, these numbers should be set significantly higher depending on resources and demand to alleviate denial-of-access attacks. Setting a lower the login grace time (time to keep pending connections alive while waiting for authorization) can be a good idea as it frees up pending connections quicker but at the expense of convenience.

By default, the OpenSSH server logs to the AUTH facility of syslog, at the INFO level. If you want to record more information - such as failed login attempts - you should increase the logging level to VERBOSE.

It's recommended to log more information if you're curious about malicious SSH traffic.

To increase the level, find the following line in your sshd_config:

and change it to this:

Ssh Config Editor Windows 10

Now all the details of ssh login attempts will be saved in your /var/log/auth.log file.

If you have started using a different port, or if you think your server is well-enough hidden not to need much security, you should increase your logging level and examine your auth.log file every so often. If you find a significant number of spurious login attempts, then your computer is under attack and you need more security.

Whatever security precautions you've taken, you might want to set the logging level to VERBOSE for a week, and see how much spurious traffic you get. It can be a sobering experience to see just how much your computer gets attacked.

If you want to try to scare novice attackers, it can be funny to display a banner containing legalese. This doesn't add any security, because anyone that's managed to break in won't care about a 'no trespassing' sign--but it might give a bad guy a chuckle.

To add a banner that will be displayed before authentication, find this line:

and replace it with:

This will display the contents of the /etc/issue.net file, which you should edit to your taste. If you want to display the same banner to SSH users as to users logging in on a local console, replace the line with:

To edit the banner itself try

Here is an example for what you might put in an issue or issue.net file and you could just copy&paste this in:

Once you have finished editing sshd_config, make sure to save your changes before restarting your SSH daemon.

First, check that your SSH daemon is running:

This command should produce a line like this:

If there is no line, your SSH daemon is not running. If it is, you should next check that it's listening for incoming connections:

This command should produce a line that looks like one of these:

If there is more than one line, in particular with a port number different than 22, then your SSH daemon is listening on more than one port - you might want to go back and delete some Port lines in your sshd_config. If there are no lines, your SSH daemon is not listening on any ports, so you need to add at least one Port line. If the line specifies something other than '*:22' ([::]:22 is IPv6), then your SSH daemon is listening on a non-standard port or address, which you might want to fix.

Next, try logging in from your own computer:

This will print a lot of debugging information, and will try to connect to your SSH server. You should be prompted to type your password, and you should get another command-line when you type your password in. If this works, then your SSH server is listening on the standard SSH port. If you have set your computer to listen on a non-standard port, then you will need to go back and comment out (or delete) a line in your configuration that reads Port 22. Otherwise, your SSH server has been configured correctly.

To leave the SSH command-line, type:

If you have a local network (such as a home or office network), next try logging in from one of the other computers on your network. If nothing happens, you might need to tell your computer's firewall to allow connections on port 22 (or from the non-standard port you chose earlier).

Finally, try logging in from another computer elsewhere on the Internet - perhaps from work (if your computer is at home) or from home (if your computer is at your work). If you can't access your computer this way, you might need to tell your router's firewall to allow connections from port 22, and might also need to configure Network Address Translation.

This tutorial walks you through creating and connecting to a virtual machine (VM) on Azure using the Visual Studio Code Remote - SSH extension. You'll create a Node.js Express web app to show how you can edit and debug on a remote machine with VS Code just like you could if the source code was local.

Note: Your Linux VM can be hosted anywhere - on your local host, on premise, in Azure, or in any other cloud, as long as the chosen Linux distribution meets these prerequisites.

Prerequisites

To get started, you need to have done the following steps:

1. Install an OpenSSH compatible SSH client (PuTTY is not supported).
2. Install Visual Studio Code.
3. Have an Azure subscription (If you don't have an Azure subscription, create a free account before you begin).

Install the extension

The Remote - SSH extension is used to connect to SSH hosts.

Remote - SSH

With the Remote - SSH extension installed, you will see a new Status bar item at the far left.

The Remote Status bar item can quickly show you in which context VS Code is running (local or remote) and clicking on the item will bring up the Remote - SSH commands.

Create a virtual machine

If you don't have an existing Linux virtual machine, you can create a new VM through the Azure portal. In the Azure portal, search for 'Virtual Machines', and choose Add. From there, you can select your Azure subscription and create a new resource group, if you don't already have one.

Note: In this tutorial, we are using Azure, but your Linux VM can be hosted anywhere, as long as the Linux distribution meets these prerequisites.

Now you can specify details of your VM, such as the name, the size, and the base image. Choose Ubuntu Server 18.04 LTS for this example, but you can choose recent versions of other Linux distros and look at VS Code's supported SSH servers.

Set up SSH

There are several authentication methods into a VM, including an SSH public/private key pair or a username and password. We strongly recommend using key-based authentication (if you use a username/password, you'll be prompted to enter your credentials more than once by the extension). If you're on Windows and have already created keys using PuttyGen, you can reuse them.

Create an SSH key

If you don't have an SSH key pair, open a bash shell or the command line and type in:

This will generate the SSH key. Press Enter at the following prompt to save the key in the default location (under your user directory as a folder named .ssh).

You will then be prompted to enter a secure passphrase, but you can leave that blank. You should now have a id_rsa.pub file which contains your new public SSH key.

Add SSH key to your VM

In the previous step, you generated an SSH key pair. Select Use existing public key in the dropdown for SSH public key source so that you can use the public key you just generated. Take the public key and paste it into your VM setup, by copying the entire contents of the id_rsa.pub in the SSH public key. You also want to allow your VM to accept inbound SSH traffic by selecting Allow selected ports and choosing SSH (22) from the Select inbound ports dropdown list.

Auto shutdown

A cool feature of using Azure VMs is the ability to enable auto shutdown (because let's face it, we all forget to turn off our VMs…). If you go to the Management tab, you can set the time you want to shut down the VM daily.

Select Review and Create, then Create, and Azure will deploy your VM for you!

Once the deployment is finished (it may take several minutes), go to the new resource view for your virtual machine.

Connect using SSH

Now that you've created an SSH host, let's connect to it!

You'll have noticed an indicator on the bottom-left corner of the Status bar. This indicator tells you in which context VS Code is running (local or remote). Click on the indicator to bring up a list of Remote extension commands.

Choose the Remote-SSH: Connect to Host command and connect to the host by entering connection information for your VM in the following format: user@hostname.

The user is the username you set when adding the SSH public key to your VM. For the hostname, go back to the Azure portal and in the Overview pane of the VM you created, copy the Public IP address.

Before connecting in Remote - SSH, you can verify you're able to connect to your VM via a command prompt using ssh user@hostname.

Note: If you run into an error ssh: connect to host <host ip> port 22: Connection timed out, you may need to delete NRMS-Rule-106 from the Networking tab of your VM:

Set the user and hostname in the connection information text box.

VS Code will now open a new window (instance). You'll then see a notification that the 'VS Code Server' is initializing on the SSH Host. Once the VS Code Server is installed on the remote host, it can run extensions and talk to your local instance of VS Code.

You'll know you're connected to your VM by looking at the indicator in the Status bar. It shows the hostname of your VM.

The Remote - SSH extension also contributes a new icon on your Activity bar, and clicking on it will open the Remote explorer. From the dropdown, select SSH Targets, where you can configure your SSH connections. For instance, you can save the hosts you connect to the most and access them from here instead of entering the user and hostname.

Once you're connected to your SSH host, you can interact with files and open folders on the remote machine. If you open the integrated terminal (⌃` (Windows, Linux Ctrl+`)), you'll see you're working inside a bash shell while you're on Windows.

You can use the bash shell to browse the file system on the VM. You can also browse and open folders on the remote home directory with File > Open Folder.

Create your Node.js application

In this step, you will create a simple Node.js application. You will use an application generator to quickly scaffold out the application from a terminal.

Install Node.js and npm

From the integrated terminal (⌃` (Windows, Linux Ctrl+`)), update the packages in your Linux VM, then install Node.js, which includes npm, the Node.js package manager.

You can verify the installations by running:

Install the Express generator

Express is a popular framework for building and running Node.js applications. You can scaffold (create) a new Express application using the Express Generator tool. The Express Generator is shipped as an npm module and installed by using the npm command-line tool npm.

The -g switch installs the Express Generator globally on your machine so that you can run it from anywhere.

Create a new application

You can now create a new Express application called myExpressApp by running:

The --view pug parameters tell the generator to use the pug template engine.

To install all of the application's dependencies, go to the new folder and run npm install.

Run the application

Last, let's ensure that the application runs. From the terminal, start the application using the npm start command to start the server.

The Express app by default runs on http://localhost:3000. You won't see anything in your local browser on localhost:3000 because the web app is running on your virtual machine.

Ssh Edit Text File

Port forwarding

To be able to browse to the web app on your local machine, you can leverage another feature called Port forwarding.

To be able to access a port on the remote machine that may not be publicly exposed, you need to establish a connection or a tunnel between a port on your local machine and the server. With the app still running, open the SSH Explorer and find the Forwarded Ports view. Click on the Forward a port link and indicate that you want to forward port 3000:

Name the connection 'browser':

The server will now forward traffic on port 3000 to your local machine. When you browse to http://localhost:3000, you see the running web app.

Edit and debug

From the Visual Studio Code File Explorer (⇧⌘E (Windows, Linux Ctrl+Shift+E)), navigate to your new myExpressApp folder and double-click the app.js file to open it in the editor.

Edit File Ssh

IntelliSense

You have syntax highlighting for the JavaScript file as well as IntelliSense with hovers, just like you would see if the source code was on your local machine.

When you start typing, you'll get smart completions for the object methods and properties.

Debugging

Set a breakpoint on line 10 of app.js by clicking in the gutter to the left of the line number or by putting the cursor on the line and pressing F9. The breakpoint will be displayed as a red circle.

Ssh Editor For Windows

Now, press F5 to run your application. If you are asked how to run the application, choose Node.js.

The app will start, and you'll hit the breakpoint. You can inspect variables, create watches, and navigate the call stack.

Press F10 to step or F5 again to finish your debugging session.

You get the full development experience of Visual Studio Code connected over SSH.

Ending your SSH connection

Ssh File Editor

You can end your session over SSH and go back to running VS Code locally with File > Close Remote Connection.

Congratulations!

Congratulations, you've successfully completed this tutorial!

Next, check out the other Remote Development extensions.

Or get them all by installing the Remote Development Extension Pack.