Knocker

I wanted to use knock servers but wasn't sure how to remember all the knock patterns, plus I pretty much always want to run specific commands straight after knocking.

I also love .ssh/config files (if you don't use one, you are missing out!), so simple yet so powerful.

Add this line to your application's Gemfile:

gem 'knocker'

And then execute:

$ bundle

Or install it yourself as:

$ gem install knocker

• a server with a configured knock daemon (such as knockd)
• the included port-knock client (knock)

Define knock patterns in your config file (at ~/.config/knocker) by using nkr -e and then run them using nkr pattern-name. Your pattern defines the host, the knock sequence and any commands to run after knocking.

Running nkr with a pattern name sends the knock sequence to the host then runs the specified commands. This allows one to easily knock on a host to open an SSH port and then run the command to SSH into the host.

With a knock daemon configured on host.example.com to open port 22 (SSH) when it hears knocks on UDP ports 3333, 2424 and 22388, one could configure a pattern as such:

pattern hiddenssh
  h host.example.com
  u 3333
  u 2424
  u 22388
  ssh robert@$host

So that running nkr hiddenssh knocks and opens the SSH port, then connects to SSH. Then the knock daemon can close the port behind you.

Like an SSH config file is powerful for connecting to SSH daemons:

# SSH config file
Host myvps # simply type ssh myvps at command prompt
  Hostname vps.example.com
  User robert
  Port 22022
  DynamicForward 50000
  LocalForward 3000:localhost:3000
  ForwardX11 yes

I want knocker to be powerful for connecting to knock daemons:

The config file stores knock patterns which include:

• hostname
• knock specs
• commands to run after knocking

# Knocker config file
# keep this secret, knock patterns are almost like passwords
pattern pvtchatops # simply type nkr pvtchatops at command prompt
  host myvps.example.com
  u 5445
  t 4456
  t 63854
  c xchat --url=irc://$host:36777/chatops

So when you run nkr pvtchatops it actually runs two commands:

• The knock client command: knock myvps.example.com 5445:udp 4456:tcp 63854:tcp
• The post command: xchat --url=irc://myvps.example.com:36777/chatops

Easy!

As you saw, the config syntax is simple.

• use pattern and a name to name the pattern
• h and then the hostname/ip to connect to
• t and the port number for a tcp knock (multiples allowed)
• u and the port number for a udp knock (multiples allowed)
• c and the command to run after knocking (multiples allowed)
• on command lines use $host to use host defined for the pattern

Mix this with SSH config files and you will an unstoppable sysadmin!

KEEP THE CONFIG FILE SECRET!!!

1. Fork it ( http://github.com/penguinpowernz/knocker/fork )
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Add some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create new Pull Request