module Net::SSH

Net::SSH is a library for interacting, programmatically, with remote processes via the SSH2 protocol. Sessions are always initiated via ::start. From there, a program interacts with the new SSH session via the convenience methods on Net::SSH::Connection::Session, by opening and interacting with new channels (Net::SSH::Connection:Session#open_channel and Net::SSH::Connection::Channel), or by forwarding local and/or remote ports through the connection (Net::SSH::Service::Forward).

The SSH protocol is very event-oriented. Requests are sent from the client to the server, and are answered asynchronously. This gives great flexibility (since clients can have multiple requests pending at a time), but it also adds complexity. Net::SSH tries to manage this complexity by providing some simpler methods of synchronous communication (see Net::SSH::Connection::Session#exec!).

In general, though, and if you want to do anything more complicated than simply executing commands and capturing their output, you'll need to use channels (Net::SSH::Connection::Channel) to build state machines that are executed while the event loop runs (Net::SSH::Connection::Session#loop).

Net::SSH::Connection::Session and Net::SSH::Connection::Channel have more information about this technique.

“Um, all I want to do is X, just show me how!”

X == “execute a command and capture the output”

Net::SSH.start("host", "user", password: "password") do |ssh|
  result = ssh.exec!("ls -l")
  puts result

X == “forward connections on a local port to a remote host”

Net::SSH.start("host", "user", password: "password") do |ssh|
  ssh.forward.local(1234, "", 80)
  ssh.loop { true }

X == “forward connections on a remote port to the local host”

Net::SSH.start("host", "user", password: "password") do |ssh|
  ssh.forward.remote(80, "", 1234)
  ssh.loop { true }



This is the set of options that ::start recognizes. See ::start for a description of each option.

Public Class Methods

assign_defaults(options) click to toggle source
# File lib/net/ssh.rb, line 286
def self.assign_defaults(options)
  if !options[:logger]
    options[:logger] =
    options[:logger].level = Logger::FATAL

  options[:password_prompt] ||= Prompt.default(options)

  %[password passphrase].each do |key|
    options.delete(key) if options.key?(key) && options[key].nil?
configuration_for(host, use_ssh_config) click to toggle source

Returns a hash of the configuration options for the given host, as read from the SSH configuration file(s). If use_ssh_config is true (the default), this will load configuration from both ~/.ssh/config and /etc/ssh_config. If use_ssh_config is nil or false, nothing will be loaded (and an empty hash returned). Otherwise, use_ssh_config may be a file name (or array of file names) of SSH configuration file(s) to read.

See Net::SSH::Config for the full description of all supported options.

# File lib/net/ssh.rb, line 276
def self.configuration_for(host, use_ssh_config)
  files = case use_ssh_config
          when true then Net::SSH::Config.expandable_default_files
          when false, nil then return {}
          else Array(use_ssh_config)

  Net::SSH::Config.for(host, files)
start(host, user=nil, options={}) { |connection| ... } click to toggle source

The standard means of starting a new SSH connection. When used with a block, the connection will be closed when the block terminates, otherwise the connection will just be returned. The yielded (or returned) value will be an instance of Net::SSH::Connection::Session (q.v.). (See also Net::SSH::Connection::Channel and Net::SSH::Service::Forward.)

Net::SSH.start("host", "user") do |ssh|
  ssh.exec! "cp /some/file /another/location"
  hostname = ssh.exec!("hostname")

  ssh.open_channel do |ch|
    ch.exec "sudo -p 'sudo password: ' ls" do |ch, success|
      abort "could not execute sudo ls" unless success

      ch.on_data do |ch, data|
        print data
        if data =~ /sudo password: /


This method accepts the following options (all are optional):

  • :auth_methods => an array of authentication methods to try

  • :bind_address => the IP address on the connecting machine to use in establishing connection. (:bind_address is discarded if :proxy is set.)

  • :check_host_ip => Also ckeck IP address when connecting to remote host. Defaults to true.

  • :compression => the compression algorithm to use, or true to use whatever is supported.

  • :compression_level => the compression level to use when sending data

  • :config => set to true to load the default OpenSSH config files (~/.ssh/config, /etc/ssh_config), or to false to not load them, or to a file-name (or array of file-names) to load those specific configuration files. Defaults to true.

  • :encryption => the encryption cipher (or ciphers) to use

  • :forward_agent => set to true if you want the SSH agent connection to be forwarded

  • :known_hosts => a custom object holding known hosts records. It must implement search_for and add in a similiar manner as KnownHosts.

  • :global_known_hosts_file => the location of the global known hosts file. Set to an array if you want to specify multiple global known hosts files. Defaults to %w(/etc/ssh/ssh_known_hosts /etc/ssh/ssh_known_hosts2).

  • :hmac => the hmac algorithm (or algorithms) to use

  • :host_key => the host key algorithm (or algorithms) to use

  • :host_key_alias => the host name to use when looking up or adding a host to a known_hosts dictionary file

  • :host_name => the real host name or IP to log into. This is used instead of the host parameter, and is primarily only useful when specified in an SSH configuration file. It lets you specify an “alias”, similarly to adding an entry in /etc/hosts but without needing to modify /etc/hosts.

  • :keepalive => set to true to send a keepalive packet to the SSH server when there's no traffic between the SSH server and Net::SSH client for the keepalive_interval seconds. Defaults to false.

  • :keepalive_interval => the interval seconds for keepalive. Defaults to 300 seconds.

  • :keepalive_maxcount => the maximun number of keepalive packet miss allowed. Defaults to 3

  • :kex => the key exchange algorithm (or algorithms) to use

  • :keys => an array of file names of private keys to use for publickey and hostbased authentication

  • :key_data => an array of strings, with each element of the array being a raw private key in PEM format.

  • :keys_only => set to true to use only private keys from keys and key_data parameters, even if ssh-agent offers more identities. This option is intended for situations where ssh-agent offers many different identites.

  • :logger => the logger instance to use when logging

  • :max_pkt_size => maximum size we tell the other side that is supported per packet. Default is 0x8000 (32768 bytes). Increase to 0x10000 (65536 bytes) for better performance if your SSH server supports it (most do).

  • :max_win_size => maximum size we tell the other side that is supported for the window.

  • :non_interactive => set to true if your app is non interactive and prefers authentication failure vs password prompt. Non-interactive applications should set it to true to prefer failing a password/etc auth methods vs. asking for password.

  • :paranoid => deprecated alias for :verify_host_key

  • :passphrase => the passphrase to use when loading a private key (default is nil, for no passphrase)

  • :password => the password to use to login

  • :port => the port to use when connecting to the remote host

  • :properties => a hash of key/value pairs to add to the new connection's properties (see Net::SSH::Connection::Session#properties)

  • :proxy => a proxy instance (see Proxy) to use when connecting

  • :rekey_blocks_limit => the max number of blocks to process before rekeying

  • :rekey_limit => the max number of bytes to process before rekeying

  • :rekey_packet_limit => the max number of packets to process before rekeying

  • :send_env => an array of local environment variable names to export to the remote environment. Names may be given as String or Regexp.

  • :timeout => how long to wait for the initial connection to be made

  • :user => the user name to log in as; this overrides the user parameter, and is primarily only useful when provided via an SSH configuration file.

  • :remote_user => used for substitution into the '%r' part of a ProxyCommand

  • :user_known_hosts_file => the location of the user known hosts file. Set to an array to specify multiple user known hosts files. Defaults to %w(~/.ssh/known_hosts ~/.ssh/known_hosts2).

  • :use_agent => Set false to disable the use of ssh-agent. Defaults to true

  • :verbose => how verbose to be (Logger verbosity constants, Logger::DEBUG is very verbose, Logger::FATAL is all but silent). Logger::FATAL is the default. The symbols :debug, :info, :warn, :error, and :fatal are also supported and are translated to the corresponding Logger constant.

  • :append_all_supported_algorithms => set to true to append all supported algorithms by net-ssh. Was the default behaviour until 2.10

  • :number_of_password_prompts => Number of prompts for the password authentication method defaults to 3 set to 0 to disable prompt for password auth method

  • :password_prompt => a custom prompt object with ask method. See Net::SSH::Prompt

  • :agent_socket_factory => enables the user to pass a lambda/block that will serve as the socket factory

    Net::SSH.start(host,user,agent_socket_factory: ->{'/foo/bar') })
    example: ->{'/foo/bar')}
  • :verify_host_key => specify how strict host-key verification should be. In order of increasing strictness:

    You can also provide an own Object which responds to verify. The argument given to verify is a hash consisting of the :key, the :key_blob, the :fingerprint and the :session. Returning true accepts the host key, returning false declines it and closes the connection.

  • :fingerprint_hash => 'MD5' or 'SHA256', defaults to 'SHA256'

If user parameter is nil it defaults to USER from ssh_config, or local username

# File lib/net/ssh.rb, line 213
def self.start(host, user=nil, options={}, &block)
  invalid_options = options.keys - VALID_OPTIONS
  if invalid_options.any?
    raise ArgumentError, "invalid option(s): #{invalid_options.join(', ')}"


  options[:user] = user if user
  options = configuration_for(host, options.fetch(:config, true)).merge(options)
  host = options.fetch(:host_name, host)

  options[:check_host_ip] = true unless options.key?(:check_host_ip)

  if options[:non_interactive]
    options[:number_of_password_prompts] = 0


  if options[:verbose]
    options[:logger].level = case options[:verbose]
                             when Integer then options[:verbose]
                             when :debug then Logger::DEBUG
                             when :info  then Logger::INFO
                             when :warn  then Logger::WARN
                             when :error then Logger::ERROR
                             when :fatal then Logger::FATAL
                             else raise ArgumentError, "can't convert #{options[:verbose].inspect} to any of the Logger level constants"

  transport =, options)
  auth =, options)

  user = options.fetch(:user, user) || Etc.getlogin
  if auth.authenticate("ssh-connection", user, options[:password])
    connection =, options)
    if block_given?
        yield connection
        connection.close unless connection.closed?
      return connection
    raise AuthenticationFailed, "Authentication failed for user #{user}@#{host}"