moul

assh

computer make your ssh client smarter
Under MIT License
By moul

config devops proxy automation ssh config-management

assh




Overview

A transparent wrapper that adds support for regex, aliases, gateways, dynamic hostnames, graphviz, json output, yaml configuration, and more to SSH.


lib-ssh wraps assh as a ProxyCommand; it means that it works seamlessly with:



For specific examples, see 3rd Party Integration


Features
Configuration features

Using Gateway from command line

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


Connect to hosta using hostb as a gateway.


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


console
$ ssh hosta/hostb
[email protected] $


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│
└─────┘ └─────┘


console
$ ssh hosta/hostb/hostc
[email protected] $


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
```yaml
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
GatewayConnectTimeout: 2
Gateways:
- direct
- hosta
```



Under the hood features

Hooks
Events
BeforeConnect

BeforeConnect is called just before assh tries to connect to the remote SSH port.


Note: BeforeConnect will be called for each SSH connection; if you use multiple gateways, it will be called for each gateways until one succeed to connect.

Example of Golang template variables:


golang
// Host: http://godoc.org/moul.io/assh/pkg/config/#Host
{{.Host.Name}} // localhost
{{.Host.HostName}} // 127.0.0.1
{{.Host.Port}} // 22
{{.Host.User}} // moul
{{.Host.Prototype}} // [email protected]:22
{{.Host}} // {"HostName":"localhost","Port":22","User":"moul","ControlPersist":"yes",...}
{{printf "%s:%s" .Host.HostName .Host.Port}} // localhost:22


OnConnect

OnConnect is called as soon as assh is connected to the remote SSH port.


Note: OnConnect is not aware of the authentication process and will always be raised.

Example of Golang template variables:


```golang
// Host: http://godoc.org/moul.io/assh/pkg/config/#Host
{{.Host.Name}} // localhost
{{.Host.HostName}} // 127.0.0.1
{{.Host.Port}} // 22
{{.Host.User}} // moul
{{.Host.Prototype}} // [email protected]:22
{{.Host}} // {"HostName":"localhost","Port":22","User":"moul","ControlPersist":"yes",...}
{{printf "%s:%s" .Host.HostName .Host.Port}} // localhost:22


// Stats: http://godoc.org/moul.io/assh/pkg/commands/#ConnectionStats
{{.Stats.ConnectedAt}} // 2016-07-20 11:19:23.467900594 +0200 CEST
```


OnConnectError

OnConnectError is called when assh fails to open a new TCP connection.

Example of Golang template variables:


```golang
// Host: http://godoc.org/moul.io/assh/pkg/config/#Host
{{.Host.Name}} // localhost
{{.Host.HostName}} // 127.0.0.1
{{.Host.Port}} // 22
{{.Host.User}} // moul
{{.Host.Prototype}} // [email protected]:22
{{.Host}} // {"HostName":"localhost","Port":22","User":"moul","ControlPersist":"yes",...}
{{printf "%s:%s" .Host.HostName .Host.Port}} // localhost:22


// Error
{{.Error}} // dial tcp: lookup localhost: no such host
```


OnDisconnect

OnDisconnect is called as the assh socket is closed.


warning: if you don't see a notification when closing an SSH connection, then you probably have ControlMaster configured; OnDisconnect is not linked to the ssh program but to its socket which may stay alive even after exiting the ssh program.

Example of Golang template variables:


```golang
// Host: http://godoc.org/moul.io/assh/pkg/config/#Host
{{.Host.Name}} // localhost
{{.Host.HostName}} // 127.0.0.1
{{.Host.Port}} // 22
{{.Host.User}} // moul
{{.Host.Prototype}} // [email protected]:22
{{.Host}} // {"HostName":"localhost","Port":22","User":"moul","ControlPersist":"yes",...}
{{printf "%s:%s" .Host.HostName .Host.Port}} // localhost:22


// Stats: http://godoc.org/moul.io/assh/pkg/commands/#ConnectionStats
{{.Stats.ConnectedAt}} // 2016-07-20 11:19:23.467900594 +0200 CEST
{{.Stats.WrittenBytes}} // 3613
{{.Stats.WrittenBytesHuman}} // 3.6kb
{{.Stats.DisconnectAt}} // 2016-07-20 11:19:29,520515792 +0200 CEST
{{.Stats.ConnectionDuration}} // 6.052615198s
{{.Stats.ConnectionDurationHuman}} // 6s
{{.Stats.AverageSpeed}} // 596.933bps
{{.Stats.AverageSpeedHuman}} // 3.4kb/s
```


BeforeConfigWrite

BeforeConfigWrite is called just before assh rewrite the ~/.ssh/config file.

Example of Golang template variables:


golang
{{.SSHConfigPath}} // ~/.ssh/config


Hooks drivers
Exec driver

Exec driver uses Golang's template system to execute a shell command


Usage: exec <binary> [args...]


```yaml
defaults:
Hooks:
OnConnect: exec echo '{{.Host}}' | jq .


executes: `echo '{"HostName":"localhost","Port":"22","User":"moul","ControlPersist":"yes",...}' | jq .
which results in printing a pretty JSON of the host
{
"HostName": "localhost",
"Port": "22",
"User": "moul",
"ControlPersist": "yes",
...
}

```


```yaml
defaults:
Hooks:
OnConnect: exec echo 'New SSH connection to {{.Host.Prototype}}.' | mail -s "SSH connection journal" [email protected]


send an email with the connection prototype

```


```yaml
defaults:
Hooks:
BeforeConfigWrite: exec cp {{.SSHConfigPath}} {{.SSHConfigPath}}.backup


make a copy of ~/.ssh/config before being rewritten

```


``yaml
defaults:
Hooks:
AfterConfigWrite: 'exec echo "# date:
date`" >> {{.SSHConfigPath}}'


Append a comment with the compilation date to the generated ~/.ssh/config file

```


```yaml
defaults:
Hooks:
AfterConfigWrite: 'exec cat /path/to/my/provider/generated/.ssh/config >> {{.SSHConfigPath}}'


Append another .ssh/config file to the generated .ssh/config file

```

The exec commands are blocking, a new driver for background tasks is planned. For now, you can run a job in background like this:


```yaml
defaults:
Hooks:
OnConnect:
- exec sleep 60 &


execute the sleep 60 command in background (non-blocking)
if you quit your ssh connection, the process will continue in background.

```


Write driver

Write driver uses Golang's template system to write out data to stdout


Usage: write <line:string...>


```yaml
defaults:
Hooks:
OnConnect:
- write New SSH connection to {{.Host.Prototype}}.


writes: "New SSH connection to [email protected]:22." on the terminal on connection

```


```yaml
defaults:
Hooks:
OnDisconnect:
- "write SSH connection to {{.Host.Name}} closed, {{ .Stats.WrittenBytes }} bytes written in {{ .Stats.ConnectionDuration }} ({{ .Stats.AverageSpeed }})"


writes: SSH connection to localhost closed, 40 bytes written.

```


Notify driver

Notify driver uses Golang's template system to open Desktop notifications.



Usage: notify <line:string...>


yaml
defaults:
Hooks:
OnConnect: notify New SSH connection to {{.Host.Prototype}}.



yaml
defaults:
Hooks:
OnDisconnect:
- "notify SSH connection to {{.Host.Name}} closed, {{ .Stats.WrittenBytes }} bytes written in {{ .Stats.ConnectionDuration }} ({{ .Stats.AverageSpeed }})"



Configuration

assh now manages the ~/.ssh/config file, take care to keep a backup your ~/.ssh/config file.


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



```yaml
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
RateLimit: 10M # 10Mbytes/second rate limiting


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
ControlMasterMkdir: 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 inherit 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
Hooks:
# Automatically backup ~/.ssh/config
BeforeConfigWrite:
- 'exec set -x; cp {{.SSHConfigPath}} {{.SSHConfigPath}}.bkp'


AfterConfigWrite:
# Concat another `ssh_config` file with the one just generated by `assh`
- 'exec cat ~/.ssh/my-heroku-generated-config >> {{.SSHConfigPath}}'

# Alert me with a Desktop notification
- notify "{{.SSHConfigPath}} has been rewritten"

OnConnect:
# Log internal information to a file
- exec printf '{{.}}' | jq . >> ~/.ssh/last_connected_host.txt

# Alert me with a Desktop notification
- notify New SSH connection to {{.Host.Prototype}} at {{.Stats.ConnectedAt}}

# Write the host prototype to the terminal stderr
- write New SSH connection to {{.Host.Prototype}}

OnDisconnect:
# write on terminal and in a Desktop notification some statistics about the finished connection
- "write SSH connection to {{.Host.HostName}} closed, {{.Stats.WrittenBytes }} bytes written in {{.Stats.ConnectionDuration}} ({{.Stats.AverageSpeed}}bps)"
- "notify SSH connection to {{.Host.HostName}} closed, {{.Stats.WrittenBytes }} bytes written in {{.Stats.ConnectionDuration}} ({{.Stats.AverageSpeed}}bps)"


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


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


For further inspiration, these assh.yml files on public GitHub projects can educate you on how people are using assh


Usage

assh usage


```
NAME:
assh - advanced ssh config


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


VERSION:
2.8.0 (HEAD)


AUTHOR(S):
Manfred Touron https://github.com/moul/assh


COMMANDS:
ping Send packets to the SSH server and display statistics
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
assh config build

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


This action is automatically done by assh when detecting configuration changes.
Running this command is useful to set up assh or repair the configuration file.


console
$ assh config build > ~/.ssh/config


assh config list

List hosts and options.


```console
$ assh config list
Listing entries


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

*.shortcut1 -> [email protected][hostname_not_specified]:22

*.shortcut2 -> [email protected][hostname_not_specified]:22

bart -> [email protected]:22

bart-access -> [email protected][hostname_not_specified]:22

dolphin -> [email protected]:24

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

homer -> [email protected]:2222

lisa-access -> [email protected][hostname_not_specified]:22

maggie -> [email protected][hostname_not_specified]:22

marvin -> [email protected][hostname_not_specified]:23

my-env-host -> [email protected][hostname_not_specified]:22

schoolgw -> [email protected]:22
ForwardX11=no [custom options]

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

vm-*.school.com -> [email protected][hostname_not_specified]:22

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


```


assh config graphviz

Generate a graphviz graph of the hosts


console
$ assh config graphviz | dot -Tpng > assh-hosts.png



assh config search <keyword>

Search for <keyword> in hosts and host options.


console
$ assh config search bart
Listing results for bart:
bart -> [email protected]:22
bart-access -> [email protected][hostname_not_specified]:22


assh info

Display system-wide information.


```console
$ 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
```


assh sockets list

List active control sockets.


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



assh sockets flush

Close active control sockets.


console
$ assh sockets flush
Closed 4 control sockets.


assh sockets master

Create a master control sockets.


console
$ assh sockets master


assh ping

Send packets to the SSH server and display stats.


```console
$ assh ping -c 4 localhost
PING localhost (127.0.0.1) PORT 22 (ssh) PROTO tcp
Connected to 127.0.0.1: seq=0 time=321µs protocol=tcp port=22
Connected to 127.0.0.1: seq=1 time=501µs protocol=tcp port=22
Connected to 127.0.0.1: seq=2 time=550µs protocol=tcp port=22
Connected to 127.0.0.1: seq=3 time=641µs protocol=tcp port=22


--- localhost assh ping statistics ---
4 packets transmitted, 4 packets received, 0.00% packet loss
round-trip min/avg/max = 321µs/503.25µs/641µs
```


Install

Get the latest version using GO (recommended way):


bash
go get -u moul.io/assh/v2


note: tested with Go1.7 or above

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


bash
brew install assh


Build the latest version


bash
brew install assh --HEAD

Get a released version on: https://github.com/moul/assh/releases

Register the wrapper (optional)

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


bash
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!


Webapp

assh contains an experimental web application hosted on heroku: https://assh.herokuapp.com/

Convert an assh.yml file to ssh_config format:


```console
$ http --form POST https://assh-dev.herokuapp.com/assh-to-ssh [email protected]~/.ssh/assh.d/test.yml | jq -r .ssh_config


This file was automatically generated by assh v2.8.0
on 2018-07-03 21:06:56 +0000 UTC, based on ~/.ssh/assh.yml

more info: https://github.com/moul/assh
host-based configuration

Host *.scw
Port 22
StrictHostKeyChecking no
User root
UserKnownHostsFile /dev/null
# ResolveCommand: /bin/sh -c "scw inspect -f {{.PublicAddress.IP}} server:$(echo %h | sed s/.scw//)"


Host lalala
Port 22
User moul
# HostName: 127.0.0.1


Host toto[0-5]toto
User samantha


global configuration

Host *
ProxyCommand assh connect --port=%p %h
```


Docker

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



console
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

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.,


```yaml
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:


yaml
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.



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.


yaml
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).


How to disable the automatic configuration rewrite

Each time you call ssh, assh will check if the generated ~/.ssh/config file is outdated.


By default, it will transparently regenerate the configuration file if needed.


You can disable this behavior by generating the configuration file like this:


bash
assh config build --no-automatic-rewrite


3rd Party Integration
Ansible

In your ansible.cfg under ssh_connection, make sure you have the following, changing the path to your assh:
[ssh_connection]
ansible_ssh_executable = '/usr/local/bin/assh wrapper ssh'


3rd Party Projects

Contributors
Code Contributors

This project exists thanks to all the people who contribute. [Contribute].


Financial Contributors

Become a financial contributor and help us sustain our community. [Contribute]


Individuals


Organizations

Support this project with your organization. Your logo will show up here with a link to your website. [Contribute]



Stargazers over time


License

© 2009-2021 Manfred Touron - MIT License