> ## Content Index > Fetch the complete content index at: https://linuxhandbook.com/llms.txt > Use this file to discover other available public pages before exploring further. # ASSH: An Advance Way to Interact with SSH - URL: https://linuxhandbook.com/assh/ - Published: 2024-02-29T16:40:15.000Z - Updated: 2024-04-12T11:40:16.000Z - Description: Enhance your SSH experience with assh when you have numerous hosts to connect to. - Author: LHB Community - Tags: SSH Advanced, #ssh, #docs-col, Tools ASSH or Advanced SSH Config is a wrapper for SSH that allows dynamic and advanced management of SSH configurations. Standard SSH configurations can quickly become complex and difficult to manage, especially in environments with many servers. ASSH offers a solution to this problem by introducing an abstraction layer. This supercharges the utilization of [SSH config file](https://linuxhandbook.com/ssh-config-file/) feature. For example, if you have a set of servers divided into development, testing, and production environments. With ASSH, you can define these environments in a clear and organized manner, making it easier to switch between them as needed. ``` # assh.yml defaults: user: talha groups: development: hosts: - dev1.example.com - dev2.example.com testing: hosts: - test1.example.com - test2.example.com production: hosts: - prod1.example.com - prod2.example.com ``` ASSH allows you to define groups of servers based on their environments which makes it easier to connect with a specific environment without listing out individual hosts. For example, to connect to dev server: ``` assh development ``` Sounds exciting? Let's see more on assh. ## How ASSH Works Let's dive into the key concepts of [ASSH](https://github.com/moul/assh?ref=linuxhandbook.com) to better understand how this tool enriches the SSH experience. ASSH is not just a wrapper; it's a clever reinvention of how we interact with SSH. ASSH works by interposing itself between your SSH client and your SSH connections. It intercepts SSH commands and manipulates them according to the configurations specified in your *\~/.ssh/config*. This allows for great flexibility and in-depth customization of your connections. The core of ASSH is based on two main components: **The Configuration Parser**: ASSH reads and interprets the SSH configuration file. It adds an extra layer of functionality while respecting the basic syntax and functionality of the original SSH file. **The SSH Proxy:** When an SSH connection is initiated, ASSH acts as a proxy. It can dynamically change connection parameters, distribute the load among multiple hosts, or even bounce through multiple servers to reach the final destination. One of the most powerful aspects of ASSH is its ability to handle complex configurations with simplicity. For example, you can configure connections through proxy servers, set automatic reconnection rules, or even manage groups of hosts with similar configurations. With ASSH, you have the ability to define advanced rules for each host or host group in your configuration file. These rules may include: - Balancing and Failover: Distribute connections across multiple hosts to balance the load or provide redundancy. - Chaining and Jump Hosts: Connect to a host through one or more intermediaries, which is particularly useful in complex or secure environments. - Custom Hooks: Run specific scripts or commands at different times during your SSH connection, like before login, after logout, etc. ## Installing ASSH Whether you're on Linux, macOS, or Windows, the installation process is designed to be as simple as possible. ASSH is easily installable through common package managers. On Linux, the process may vary slightly depending on your distribution, but ASSH is generally available through standard package managers. ASSH can also be installed with [asdf-vm](https://asdf-vm.com/?ref=linuxhandbook.com): ``` asdf plugin add assh asdf install assh latest asdf global assh latest ``` ## ASSH Configuration Files After installing ASSH, it is essential to understand how configuration files are defined. The file *\~/.ssh/config* is a standard text file that defines settings for SSH connections. This file may include information like hostnames, IP addresses, usernames, ports, and other configuration options. Here is an example of what a basic entry in this file might look like: ``` Host myserver HostName myserver.example.com User myuser Port 22 IdentityFile ~/.ssh/id_ed25519 ``` In this example, myserver is an alias for the SSH connection to the server *myserver.example.com*. This file also specifies the username, port, and SSH identity file to use for this connection. ``` Host *.example.com User myuser IdentityFile ~/.ssh/id_ed25519 ControlMaster auto ControlPath ~/.ssh/cm-%r@%h:%p ControlPersist 5m ``` In this example, *\*.example.com* is a template for SSH connecting to servers whose domain name ends with .example.com. This template also specifies the user name, SSH identity file, and connections settings to use for this connection. In this example ControlMaster enables SSH connection multiplexing. Here it is set to auto which tells SSH to try to use an existing connection to the same host instead of creating a new one and ControlPath as the name suggests specifies the location for the control socket. Similarly, ControlPresist specfies how long master connection will remain open after the client connections are shut. ## Building SSH File ASSH uses its own configuration file, named .assh.yml, to build the SSH file. In this configuration file assh adds its own options and functionalities. For example, with ASSH, you can define templates for common configurations, use hooks to trigger specific actions and much more. Let's see this in detail with a first, fairly simplistic example: ``` hosts: on1.talha.local: User:talha ``` In this example, *on1.talha.local* will log in with user *talha*. ## Generating the SSH File The first thing to do before starting anything is to save the current file: ``` cp ~/.ssh/config ~/.ssh.config.orig ``` To build or update your SSH configuration file, use the following command: ``` assh config build ``` This command allows ASSH to generate an enriched SSH configuration file, taking into account advanced ASSH features . Here is the content generated with the file above: ``` #This file was automatically generated by assh vn/a (n/a) #on 2024-02-28 01:21:27 +0100 CET, based on ~/.ssh/assh.yml # # more info: https://github.com/moul/assh # host-based configuration Host on1.talha.local User talha # global configuration Host * ProxyCommand /home/bob/.asdf/installs/assh/2.16.0/bin/assh connect --port=%p %h ``` If you read correctly the wrapper assh is used each time the ssh. ## Validating Configuration To check that everything is in order, you can test your configuration by establishing an SSH connection to one of your servers: ``` ssh on1.talha.local ``` If the connection is successful, ASSH is correctly installed and configured. ## Advance Settings The default settings in ASSH serve as the base configuration for all hosts that do not explicitly specify certain settings. This is particularly useful in environments with many servers, as it helps maintain a uniform and centralized configuration. To configure default settings in ASSH, you must define a section defaults in your file. Here is an example of configuring the default settings: ``` defaults User defaultuser Port 22 IdentityFile ~/.ssh/id_ed25519 ForwardAgent yes ControlMaster auto ControlPath ~/.ssh/multiplex/%r@%h:%p ControlPersist 10m ``` In this example, all hosts will inherit these default settings unless they are overridden in the host-specific configuration. Although the default settings are applied to all hosts, you can still override them for specific hosts. For example: ``` Host specialserver HostName special.example.com User specialuser Port 2222 ``` In this case, specialserver will use a different user and port than those defined in the default settings. ## Creating Templates A template in ASSH is a kind of configuration template that can be applied to multiple entries in your *\~/.ssh/config.* This allows you to define a base configuration and reuse it for different hosts, avoiding redundancy and making configurations easier to maintain. To create a template in ASSH, you start by defining a section *Templates* in your configuration file. For example : ``` templates: my-template: User: bart ``` In this example, *my-template* is a template that defines a common parameter: the user. To apply this template to a host, simply reference the template name in the host configuration: ``` Host server1 Inherits my-template HostName server1.example.com Host server2 Inherits my-template HostName server2.example.com ``` Here, *server1* and *server2* both inherit the settings defined in *my-template*, which ensures consistency in configuration while reducing duplication. ## Other ASSH CLI Commands The ASSH Command Line Interface (CLI) offers several commands under *assh config* which you can efficiently manage your SSH configurations. These commands allow you to build, visualize and manipulate the configuration in an advanced way. **Graphical Visualization of Hosts** The command `assh config graphvizgenerates` a graphical representation of your hosts and their relationships, in Graphviz format. ``` assh config graphviz digraph G { "10.0.0.*"->"vr1.talha.local"[ color=red, label=1 ]; "machine*"->"vr1.talha.local"[ color=red, label=1 ]; "10.0.0.*" [ color=blue ]; "machine*" [ color=blue ]; "vr1.talha.local" [ color=blue ]; } ``` ![Graphical representation of assh](https://linuxhandbook.com/content/images/2024/02/graphviz.svg) This can be extremely useful for visualizing complex configurations, especially when you have dependencies or relationships between different hosts, such as gateways or cascading configurations. **Output in JSON** The command `assh config json` provides a JSON representation of your configuration. This is a useful feature for integration with other tools or for automated processing. ``` assh config json { "hosts": { "10.0.0.*": { "User": "root", "Gateways": [ "vr1.talha.local" ] }, "192.168.3.*": { "User": "ubuntu" }, "machine*": { "User": "talha", "Gateways": [ "vr1.talha.local" ] }, "on1.talha.local": { "User": "talha" }, "proxmox": { "User": "root", "Aliases": [ "proxmox.talha.local" ] }, "proxmox2": { "User": "root", "Aliases": [ "proxmox2.talha.local" ] }, "vr1.talha.local": { "User": "root" } }, "templates": {}, "defaults": { "StrictHostKeyChecking": "no", "UserKnownHostsFile": [ "/dev/null" ], "Hooks": {} }, "asshknownhostfile": "~/.ssh/assh_known_hosts" } ``` This command can be used to parse and process your SSH configuration in scripts or applications that consume JSON data. **Searching Configuration** Finally, the command `assh config search`allows you to search for specific entries in your configuration using search text. ``` assh config search proxmox Listing results for proxmox: proxmox -> root@proxmox:22 proxmox2 -> root@proxmox2:22 ``` This command is extremely useful when you are working with a large number of hosts and need to find specific information quickly. ## Final Words ASSH is a revolutionizing tool that changes the way you manage your SSH configuration. From initial configuration and default settings to advanced use of templates, and the CLI, ASSH proves to be an indispensable ally for any system administrator. ✍️ ****Author**: Talha Khalid is a freelance web developer and technical writer.