advanced-ssh-config

assh - Advanced SSH config

Table of Contents

1. Overview
2. Features

• Configuration features
• Using Gateway from command line
• Using Gateway from configuration file
• Under the hood features

1. Configuration
2. Usage

• Usage Examples

1. Install

• Register the wrapper (optional)

1. Getting started
2. Changelog
3. Alternative version
4. Troobleshooting
5. License

Overview

A transparent wrapper that adds regex, aliases, gateways, includes, dynamic hostnames to SSH.

Advanced SSH config is wrapped in lib-ssh as a ProxyCommand, it means that it works seamlessly with:

• ssh
• scp
• rsync
• git
• Desktop applications depending on lib-ssh or ssh (i.e: Tower, Atom.io, SSH Tunnel Manager)

Features

Configuration features

• regex support
• aliases gate -> gate.domain.tld
• gateways -> transparent ssh connection chaining
• includes: split configuration in multiple files
• local command execution: finally the reverse of RemoteCommand
• templates: equivalent to host but you can't connect directly to a template, perfect for inheritance
• inheritance: make hosts inherits from host hosts or templates
• variable expansion: resolve variables from environment
• smart proxycommand: RAW tcp connection when possible with netcat and socat as default fallbacks

Using Gateway from command line

assh can use the ProxyCommand with netcat feature of OpenSSH transparently and without the pain of using long configuration.

Connect to hosta using hostb as gateway.

  ┌─────┐
  │ YOU │─ ─ ─ ─ ─
  └─────┘         │
     ┃            ▽
     ┃         ┌─────┐
 firewall      │hostb│
     ┃         └─────┘
     ▼            │
  ┌─────┐
  │hosta│◁─ ─ ─ ─ ┘
  └─────┘

$ ssh hosta/hostb
user@hosta $

Equivalent to ssh -o ProxyCommand="ssh hostb nc %h %p" hosta

---

Connect to hosta using hostb as a gateway using hostc as a gateway.

  ┌─────┐              ┌─────┐
  │ YOU │─ ─ ─ ─ ─ ─ ─▷│hostc│
  └─────┘              └─────┘
     ┃                    │
     ┃
 firewall                 │
     ┃
     ┃                    │
     ▼                    ▽
  ┌─────┐              ┌─────┐
  │hosta│◁─ ─ ─ ─ ─ ─ ─│hostb│
  └─────┘              └─────┘

$ ssh hosta/hostb/hostc
user@hosta $

Equivalent to ssh -o ProxyCommand="ssh -o ProxyCommand='ssh hostc nc %h %p' hostb nc %h %p" hosta

Using Gateways from configuration file

You can define an equivalent of the "ProxyCommand with netcat" feature of OpenSSH, with a simpler syntax, more advanced workflows and a unique fallback feature.

Let's consider the following assh.yml file

hosts:
  hosta:
    Hostname: 1.2.3.4

  hostb:
    Hostname: 5.6.7.8
    Gateways:
    - hosta

  hostc:
    Hostname: 9.10.11.12
    Gateways:
    - hostb

  hostd:
    Hostname: 13.14.15.16
    Gateways:
    - direct
    - hosta

• ssh hosta -> ssh 1.2.3.4
• ssh hostb -> ssh -o ProxyCommand="ssh hostb nc %h %p" hosta
• ssh hostc -> ssh -o ProxyCommand="ssh -o ProxyCommand='ssh hostc nc %h %p' hostb nc %h %p" hosta
• ssh hostd ->
  • assh will try to ssh 13.14.15.16
  • then, fallback on ssh -o ProxyCommand="ssh hostd nc %h %p" hosta
  • this method allows you to have the best performances when it is possible, but ensure your commands will work if you are outside of your company for instance

Under the hood features

• Automatically regenerates ~/.ssh/config file when needed
• Inspect parent process to determine log level (if you use ssh -vv, assh will automatically be ran in debug mode)
• Automatically creates ControlPath directories so you can use slashes in your ControlPath option, can be disabled with the NoControlMasterMkdir: true configuration in host or globally.

Configuration

The ~/.ssh/config file is now managed by assh, take care to keep a backup your ~/.ssh/config file.

~/.ssh/assh.yml is a YAML file containing:

• an hosts dictionary containing multiple HOST definitions
• a defaults section containing global flags
• and an includes section containing path to other configuration files

hosts:

  homer:
    # ssh homer ->  ssh 1.2.3.4 -p 2222 -u robert
    Hostname: 1.2.3.4
    User: robert
    Port: 2222

  bart:
    # ssh bart ->   ssh 5.6.7.8 -u bart           <- direct access
    #            or ssh 5.6.7.8/homer -u bart     <- using homer as a gateway
    Hostname: 5.6.7.8
    User: bart
    Gateways:
    - direct                   # tries a direct access first
    - homer                    # fallback on homer gateway

  maggie:
    # ssh maggie ->   ssh 5.6.7.8 -u maggie       <- direct access
    #              or ssh 5.6.7.8/homer -u maggie   <- using homer as a gateway
    User: maggie
    Inherits:
    - bart                     # inherits rules from "bart"

  bart-access:
    # ssh bart-access ->  ssh home.simpson.springfield.us -u bart
    Inherits:
    - bart-template
    - simpson-template

  lisa-access:
    # ssh lisa-access ->  ssh home.simpson.springfield.us -u lisa
    Inherits:
    - lisa-template
    - simpson-template

  marvin:
    # ssh marvin    -> ssh marvin    -p 23
    # ssh sad-robot -> ssh sad-robot -p 23
    # ssh bighead   -> ssh bighead   -p 23
    # aliases inherit everything from marvin, except hostname
    Port: 23
    Aliases:
    - sad-robot
    - bighead

  dolphin:
    # ssh dolphin   -> ssh dolphin -p 24
    # ssh ecco      -> ssh dolphin -p 24
    # same as above, but with fixed hostname
    Port: 24
    Hostname: dolphin
    Aliases:
    - ecco

  schooltemplate:
    User: student
    IdentityFile: ~/.ssh/school-rsa
    ForwardX11: yes

  schoolgw:
    # ssh school ->   ssh gw.school.com -l student -o ForwardX11=no -i ~/.ssh/school-rsa
    Hostname: gw.school.com
    ForwardX11: no
    Inherits:
    - schooltemplate

  "expanded-host[0-7]*":
    # ssh somehost2042 ->       ssh somehost2042.some.zone
    Hostname: "%h.some.zone"

  vm-*.school.com:
    # ssh vm-42.school.com ->   ssh vm-42.school.com/gw.school.com -l student -o ForwardX11=yes -i ~/.ssh/school-rsa
    Gateways:
    - schoolgw
    Inherits:
    - schooltemplate
    # do not automatically create `ControlPath` -> may result in error
    NoControlMasterMkdir: true

  "*.shortcut1":
    ResolveCommand: /bin/sh -c "echo %h | sed s/.shortcut1/.my-long-domain-name.com/"

  "*.shortcut2":
    ResolveCommand: /bin/sh -c "echo $(echo %h | sed s/.shortcut2//).my-other-long-domain-name.com"

  "*.scw":
    # ssh toto.scw -> 1. dynamically resolves the IP address
    #                 2. ssh {resolved ip address} -u root -p 22 -o UserKnownHostsFile=null -o StrictHostKeyChecking=no
    # requires github.com/scaleway/scaleway-cli
    ResolveCommand: /bin/sh -c "scw inspect -f {{.PublicAddress.IP}} server:$(echo %h | sed s/.scw//)"
    User: root
    Port: 22
    UserKnownHostsFile: /dev/null
    StrictHostKeyChecking: no

  my-env-host:
    User: user-$USER
    Hostname: ${HOSTNAME}${HOSTNAME_SUFFIX}

templates:
  # Templates are similar to Hosts, you can inherits from them
  # but you cannot ssh to a template
  bart-template:
    User: bart
  lisa-template:
    User: lisa
  simpson-template:
    Host: home.simpson.springfield.us

defaults:
  # Defaults are applied to each hosts
  ControlMaster: auto
  ControlPath: ~/tmp/.ssh/cm/%h-%p-%r.sock
  ControlPersist: yes
  Port: 22
  User: bob

includes:
- ~/.ssh/assh.d/*.yml
- /etc/assh.yml
- $ENV_VAR/blah-blah-*/*.yml

ASSHBinaryPath: ~/bin/assh  # optionally set the path of assh

---

A HOST and the defaults section may

Usage

assh usage

NAME:
   assh - advanced ssh config

USAGE:
   assh [global options] command [command options] [arguments...]

VERSION:
   2.4.1 (HEAD)

AUTHOR(S):
   Manfred Touron <https://github.com/moul/advanced-ssh-config>

COMMANDS:
   info          Display system-wide information
   config        Manage ssh and assh configuration
   sockets       Manage control sockets
   help, h       Shows a list of commands or help for one command

GLOBAL OPTIONS:
  --config value, -c value       Location of config file (default: "~/.ssh/assh.yml") [$ASSH_CONFIG]
  --debug, -D                    Enable debug mode [$ASSH_DEBUG]
  --verbose, -V                  Enable verbose mode
  --help, -h                     show help
  --version, -v                  print the version

Usage examples

Rewrites and replaces the existing ~/.ssh/config file.

This action is automatically done by assh when detecting configuration changes. Running this command manually is useful to setup assh.

$ assh config build > ~/.ssh/config

List hosts and options.

$ assh config list
Listing entries

    *.scw -> root@[hostname_not_specified]:22
        [custom options] StrictHostKeyChecking=no UserKnownHostsFile=/dev/null

    *.shortcut1 -> bob@[hostname_not_specified]:22

    *.shortcut2 -> bob@[hostname_not_specified]:22

    bart -> bart@5.6.7.8:22

    bart-access -> bob@[hostname_not_specified]:22

    dolphin -> bob@dolphin:24

    expanded-host[0-7]* -> bob@%h.some.zone:22

    homer -> robert@1.2.3.4:2222

    lisa-access -> bob@[hostname_not_specified]:22

    maggie -> maggie@[hostname_not_specified]:22

    marvin -> bob@[hostname_not_specified]:23

    my-env-host -> user-moul@[hostname_not_specified]:22

    schoolgw -> bob@gw.school.com:22
        [custom options] ForwardX11=no

    schooltemplate -> student@[hostname_not_specified]:22
        [custom options] ForwardX11=yes IdentityFile=~/.ssh/school-rsa

    vm-*.school.com -> bob@[hostname_not_specified]:22

    (*) General options:
        ControlMaster: auto
        ControlPath: ~/tmp/.ssh/cm/%h-%p-%r.sock
        ControlPersist: yes
        Port: 22
        User: bob

Search for <keyword> in hosts and host options.

$ assh config search bart
Listing results for bart:
    bart -> bart@5.6.7.8:22
    bart-access -> moul@[hostname_not_specified]:22

Display system-wide information.

$ assh info
Debug mode (client): false
CLI Path: /path/to/assh
Go version: go1.6.2
OS/Arch: darwin/amd64

RC files:
- ~/.ssh/assh.yml
- ~/.ssh/assh.d/hosts.yml
- ~/.ssh/assh.d/moul.yml
- ~/.ssh/assh.d/test.yml

Statistics:
- 299 hosts
- 2 templates
- 4 included files

List active control sockets.

$ assh sockets list
4 active control sockets in "~/.ssh/cm/":

- bart/homer/lisa-22-root.sock (14 minutes)
- bart/homer-22-root.sock (14 minutes)
- bart-22-root.sock (14 minutes)
- marge-22-bart.sock (1 hour)

Close active control sockets.

$ assh sockets flush
Closed 4 control sockets.

Create a master control sockets.

$ assh sockets master

Install

Get the latest version using GO (recommended way):

go get -u github.com/moul/advanced-ssh-config/cmd/assh

---

Get the latest released version using homebrew (Mac OS X):

brew install assh

Build the latest version

brew install assh --HEAD

---

Get a released version on: https://github.com/moul/advanced-ssh-config/releases

---

Register the wrapper (optional)

To improve experience when using advanced pattern matching, add the following at the end of your .bashrc or .zshrc:

alias ssh="assh wrapper ssh"

This step is not mandatory but highly recommended.

---

Note: ssh does not understand advanced patterns; To bypass this limitation, assh maintains a list of known hosts and regenerate the ~/.ssh/config with all those expanded known hosts.

Without the wrapper, the ~/.ssh/config risks to be outdated when connecting to a new host for the first time and you will need to launch the command again.

With the wrapper, ssh will always be called with an updated ~/.ssh/config file.

Getting started

1. Backup your old ~/.ssh/config: cp ~/.ssh/config ~/.ssh/config.backup
2. Create a new ~/.ssh/assh.yml file
3. Run assh config build > ~/.ssh/config to validate the syntax of your ~/.ssh/assh.yml file and automatically build your ~/.ssh/config file
4. You are ready!

Changelog

v2.4.1 (2016-07-19)

• Fix panic in assh wrapper (#157)

Full commits list

v2.4.0 (2016-07-14)

• Add a control socket manager assh sockets {list,flush,master} (#152)
• Add a assh --config=/path/to/assh.yml option
• Add storm-like assh config list and assh config search {keyword} commands (#151)
• Add an optional ASSHBinaryPath variable in the assh.yml file (#148)
• Rename assh proxy -> assh connect
• Hide assh connect and assh wrapper from the help
• Support built-in ssh netcat mode, may fail with older SSH clients (#146)

Full commits list

v2.3.0 (2016-04-27)

• Add wrapper and known_hosts support to handle advanced patterns (#122)
• Add build information in .ssh/config header (#49)
• Add Autocomplete support (#48)
• Initial Aliases support (#133)
• Use args[0] as ProxyCommand (#134)
• Add NoControlMasterMkdir option to disable automatic creation of directories for gateways (#124)
• Fix: Allow $(...) syntax in the ResolveCommand function (#117)
• Printing the error of a failing ResolveCommand (#117)
• Fix: Gateways field is no longer ignored when the HostName field is present (#102)
• Ignore SIGHUP, close goroutines and export written bytes (#112) (@QuentinPerez)
• Various documentation improvements (@ashmatadeen, @loliee, @cerisier)
• Support of new SSH configuration fields (AskPassGUI, GSSAPIClientIdentity, GSSAPIKeyExchange, GSSAPIRenewalForcesRekey, GSSAPIServerIdentity, GSSAPITrustDns, KeychainIntegration)

Full commits list

v2.2.0 (2016-02-03)

• Avoid exiting when an included file contains errors (#95)
• Anonymize paths in assh info
• Support of assh proxy --dry-run option
• Fix: do not resolve variables in hostnames twice (#103)

Full commits list

v2.1.0 (2015-10-05)

• Expand environment variables (#86)
• Add homebrew support (#73)
• Add a 'ssh info' command (#71)
• Templates support (#52)
• Configuration is now case insensitive (#51)
• Fix: resolving host fields for gateways (#79)
• Fix: inheritance was not working for non assh-related fields (#54)
• Fix: expanding variables in HostName (#56)

Full commits list

v2.0.0 (2015-09-07)

• First Golang version
• Compatibility issue: complete switch from .ini file format to .yml, the ~/.ssh/assh.yml file needs to be manually crafted
• Features
  • Parses ~/.ssh/assh.yml and generates ~/.ssh/config dynamically
  • CLI: Use gateways from CLI without any configuration needed
  • Config: Declares gateways in coniguration
  • Config: Host inheritance
  • Config: Support of includes
  • Config: Support of Regex
  • Config: Handling all sshconfig fields
  • Config: Support of host ProxyCommand (inception)
  • Under the hood: Inspecting parent process verbose/debug mode
  • Under the hook: dynamic proxy using raw TCP, netcat

Full commits list

v1 (2015-07-22)

• Last Python version

POC (2010-08-26)

• First Python version (POC)

Docker

Experimental: assh may run in Docker, however you will have limitations:

• The assh containers does not have any binaries except assh, you can't use ProxyCommand, ResolveCommand...
• Docker may run on another host, ssh localhost will ssh to Docker host

docker run -it --rm -v ~/.ssh:/.ssh moul/assh --help

assh in Docker is slower and has more limitations, but it may be useful for testing or if you plan to use a Docker host as a remote Gateway

Alternative version

• v1 (2009-2015) - The original implementation. It worked quite well, but was a lot slower, less portable, harder to install for the user and harder to work on to develop new features and fix bugs

Troubleshooting

I can't use gateways

assh uses the built-in netcat mode of OpenSSH (shipped with OpenSSH 5.4) by default. If your ssh client doesn't support this feature, you can configure a custom ProxyCommand configuration, i.e:

hosts:
  myserver:
    host: 1.2.3.4
    gateways:
    - mygateway
    # configure a custom proxycommand
    proxycommand: /bin/nc %h %p

  mygateway:
    host: 5.6.7.8

---

You can configure this rule globally:

defaults:
  proxycommand: nc %h %p

---

Also, be sure to have netcat installed on your system, or use an alternative proxy binary, i.e: socat.

How to configure resolver to parse /etc/hosts and/or handle mDNS requests ?

assh resolves hostnames using the system built-in resolver, depending on the OS, you can enable new features and/or change modules order.

• Linux - nsswitch documentation
• Linux - mDNS support (nss-mdns)
• Mac OS X - /etc/resolv.conf documentation

unix_listener: "/Users/.../.ssh/cm/..." too long for Unix domain socket

Starting with OpenSSH v6.7 the socket name can be shortened by configuring %C for the name expansion.

defaults:
  ControlPath: ~/tmp/.ssh/cm/%C.sock

%C is a unique identifier based on a hash of the tuple of (local host, remote user, hostname, port).

License

© 2009-2016 Manfred Touron - MIT License