Class Net::SSH::Connection::Session

  1. lib/net/ssh/connection/session.rb
Parent: Object

A session class representing the connection service running on top of the SSH transport layer. It manages the creation of channels (see open_channel), and the dispatching of messages to the various channels. It also encapsulates the SSH event loop (via loop and process), and serves as a central point-of-reference for all SSH-related services (e.g. port forwarding, SFTP, SCP, etc.).

You will rarely (if ever) need to instantiate this class directly; rather, you’ll almost always use Net::SSH.start to initialize a new network connection, authenticate a user, and return a new connection session, all in one call.

Net::SSH.start("localhost", "user") do |ssh|
  # 'ssh' is an instance of Net::SSH::Connection::Session
  ssh.exec! "/etc/init.d/some_process start"

Included modules

  1. Constants
  2. Loggable

Classes and Modules

Class Net::SSH::Connection::Session::NilChannel


MAP = Constants.constants.inject({}) do |memo, name| value = const_get(name) next unless Integer === value memo[value] = name.downcase.to_sym


options [R] The map of options that were used to initialize this instance.
properties [R] The collection of custom properties for this instance. (See #[] and #[]=).
transport [R] The underlying transport layer abstraction (see Net::SSH::Transport::Session).

Public class methods

new (transport, options={})

Create a new connection service instance atop the given transport layer. Initializes the listeners to be only the underlying socket object.

[show source]
    # File lib/net/ssh/connection/session.rb, line 62
62:     def initialize(transport, options={})
63:       self.logger = transport.logger
65:       @transport = transport
66:       @options = options
68:       @channel_id_counter = -1
69:       @channels =
70:       @listeners = { transport.socket => nil }
71:       @pending_requests = []
72:       @channel_open_handlers = {}
73:       @on_global_request = {}
74:       @properties = (options[:properties] || {}).dup
75:     end

Public instance methods

[] (key)

Retrieves a custom property from this instance. This can be used to store additional state in applications that must manage multiple SSH connections.

[show source]
    # File lib/net/ssh/connection/session.rb, line 80
80:     def [](key)
81:       @properties[key]
82:     end
[]= (key, value)

Sets a custom property for this instance.

[show source]
    # File lib/net/ssh/connection/session.rb, line 85
85:     def []=(key, value)
86:       @properties[key] = value
87:     end
busy? (include_invisible=false)

Returns true if there are any channels currently active on this session. By default, this will not include “invisible” channels (such as those created by forwarding ports and such), but if you pass a true value for include_invisible, then those will be counted.

This can be useful for determining whether the event loop should continue to be run.

ssh.loop { ssh.busy? }
[show source]
     # File lib/net/ssh/connection/session.rb, line 134
134:     def busy?(include_invisible=false)
135:       if include_invisible
136:         channels.any?
137:       else
138:         channels.any? { |id, ch| !ch[:invisible] }
139:       end
140:     end
close ()

Closes the session gracefully, blocking until all channels have successfully closed, and then closes the underlying transport layer connection.

[show source]
     # File lib/net/ssh/connection/session.rb, line 107
107:     def close
108:       info { "closing remaining channels (#{channels.length} open)" }
109:       channels.each { |id, channel| channel.close }
110:       loop { channels.any? }
111:       transport.close
112:     end
closed? ()

Returns true if the underlying transport has been closed. Note that this can be a little misleading, since if the remote server has closed the connection, the local end will still think it is open until the next operation on the socket. Nevertheless, this method can be useful if you just want to know if you have closed the connection.

[show source]
     # File lib/net/ssh/connection/session.rb, line 100
100:     def closed?
101:       transport.closed?
102:     end
exec (command, &block)

A convenience method for executing a command and interacting with it. If no block is given, all output is printed via $stdout and $stderr. Otherwise, the block is called for each data and extended data packet, with three arguments: the channel object, a symbol indicating the data type (:stdout or :stderr), and the data (as a string).

Note that this method returns immediately, and requires an event loop (see Session#loop) in order for the command to actually execute.

This is effectively identical to calling open_channel, and then Net::SSH::Connection::Channel#exec, and then setting up the channel callbacks. However, for most uses, this will be sufficient.

ssh.exec "grep something /some/files" do |ch, stream, data|
  if stream == :stderr
    puts "ERROR: #{data}"
    puts data
[show source]
     # File lib/net/ssh/connection/session.rb, line 319
319:     def exec(command, &block)
320:       open_channel do |channel|
321:         channel.exec(command) do |ch, success|
322:           raise "could not execute command: #{command.inspect}" unless success
324:           channel.on_data do |ch2, data|
325:             if block
326:     , :stdout, data)
327:             else
328:               $stdout.print(data)
329:             end
330:           end
332:           channel.on_extended_data do |ch2, type, data|
333:             if block
334:     , :stderr, data)
335:             else
336:               $stderr.print(data)
337:             end
338:           end
339:         end
340:       end
341:     end
exec! (command, &block)

Same as exec, except this will block until the command finishes. Also, if a block is not given, this will return all output (stdout and stderr) as a single string.

matches = ssh.exec!("grep something /some/files")
[show source]
     # File lib/net/ssh/connection/session.rb, line 348
348:     def exec!(command, &block)
349:       block ||= do |ch, type, data|
350:         ch[:result] ||= ""
351:         ch[:result] << data
352:       end
354:       channel = exec(command, &block)
355:       channel.wait
357:       return channel[:result]
358:     end
forward ()

Returns a reference to the Net::SSH::Service::Forward service, which can be used for forwarding ports over SSH.

[show source]
     # File lib/net/ssh/connection/session.rb, line 417
417:     def forward
418:       @forward ||=
419:     end
host ()

Returns the name of the host that was given to the transport layer to connect to.

[show source]
    # File lib/net/ssh/connection/session.rb, line 91
91:     def host
93:     end
listen_to (io, &callback)

Adds an IO object for the event loop to listen to. If a callback is given, it will be invoked when the io is ready to be read, otherwise, the io will merely have its fill method invoked.

Any io value passed to this method must have mixed into it the Net::SSH::BufferedIo functionality, typically by calling extend on the object.

The following example executes a process on the remote server, opens a socket to somewhere, and then pipes data from that socket to the remote process’ stdin stream:

channel = ssh.open_channel do |ch|
  ch.exec "/some/process/that/wants/input" do |ch, success|
    abort "can't execute!" unless success

    io =, port)

    ch.on_process do
      if io.available > 0

    ch.on_close do

[show source]
     # File lib/net/ssh/connection/session.rb, line 405
405:     def listen_to(io, &callback)
406:       listeners[io] = callback
407:     end
loop (wait=nil, &block)

The main event loop. Calls process until process returns false. If a block is given, it is passed to process, otherwise a default proc is used that just returns true if there are any channels active (see busy?). The # wait parameter is also passed through to process (where it is interpreted as the maximum number of seconds to wait for to return).

# loop for as long as there are any channels active

# loop for as long as there are any channels active, but make sure
# the event loop runs at least once per 0.1 second

# loop until ctrl-C is pressed
int_pressed = false
trap("INT") { int_pressed = true }
ssh.loop(0.1) { not int_pressed }
[show source]
     # File lib/net/ssh/connection/session.rb, line 159
159:     def loop(wait=nil, &block)
160:       running = block || { busy? }
161:       loop_forever { break unless process(wait, &running) }
162:     end
loop_forever (wait=nil, &block)

Alias for loop

on_global_request (type, &block)

Registers a handler to be invoked when the server sends a global request of the given type. The callback receives the request data as the first parameter, and true/false as the second (indicating whether a response is required). If the callback sends the response, it should return :sent. Otherwise, if it returns true, REQUEST_SUCCESS will be sent, and if it returns false, REQUEST_FAILURE will be sent.

[show source]
     # File lib/net/ssh/connection/session.rb, line 441
441:     def on_global_request(type, &block)
442:       old, @on_global_request[type] = @on_global_request[type], block
443:       old
444:     end
on_open_channel (type, &block)

Registers a handler to be invoked when the server wants to open a channel on the client. The callback receives the connection object, the new channel object, and the packet itself as arguments, and should raise ChannelOpenFailed if it is unable to open the channel for some reason. Otherwise, the channel will be opened and a confirmation message sent to the server.

This is used by the Net::SSH::Service::Forward service to open a channel when a remote forwarded port receives a connection. However, you are welcome to register handlers for other channel types, as needed.

[show source]
     # File lib/net/ssh/connection/session.rb, line 431
431:     def on_open_channel(type, &block)
432:       channel_open_handlers[type] = block
433:     end
open_channel (type="session", *extra, &on_confirm)

Requests that a new channel be opened. By default, the channel will be of type “session”, but if you know what you’re doing you can select any of the channel types supported by the SSH protocol. The extra parameters must be even in number and conform to the same format as described for Net::SSH::Buffer.from. If a callback is given, it will be invoked when the server confirms that the channel opened successfully. The sole parameter for the callback is the channel object itself.

In general, you’ll use open_channel without any arguments; the only time you’d want to set the channel type or pass additional initialization data is if you were implementing an SSH extension.

channel = ssh.open_channel do |ch|
  ch.exec "grep something /some/files" do |ch, success|

[show source]
     # File lib/net/ssh/connection/session.rb, line 287
287:     def open_channel(type="session", *extra, &on_confirm)
288:       local_id = get_next_channel_id
289:       channel =, type, local_id, &on_confirm)
291:       msg = Buffer.from(:byte, CHANNEL_OPEN, :string, type, :long, local_id,
292:         :long, channel.local_maximum_window_size,
293:         :long, channel.local_maximum_packet_size, *extra)
294:       send_message(msg)
296:       channels[local_id] = channel
297:     end
postprocess (readers, writers)

This is called internally as part of process. It loops over the given arrays of reader IO’s and writer IO’s, processing them as needed, and then calls Net::SSH::Transport::Session#rekey_as_needed to allow the transport layer to rekey. Then returns true.

[show source]
     # File lib/net/ssh/connection/session.rb, line 223
223:     def postprocess(readers, writers)
224:       Array(readers).each do |reader|
225:         if listeners[reader]
226:           listeners[reader].call(reader)
227:         else
228:           if
229:             reader.close
230:             stop_listening_to(reader)
231:           end
232:         end
233:       end
235:       Array(writers).each do |writer|
236:         writer.send_pending
237:       end
239:       transport.rekey_as_needed
241:       return true
242:     end
preprocess () {|self| ...}

This is called internally as part of process. It dispatches any available incoming packets, and then runs Net::SSH::Connection::Channel#process for any active channels. If a block is given, it is invoked at the start of the method and again at the end, and if the block ever returns false, this method returns false. Otherwise, it returns true.

[show source]
     # File lib/net/ssh/connection/session.rb, line 211
211:     def preprocess
212:       return false if block_given? && !yield(self)
213:       dispatch_incoming_packets
214:       channels.each { |id, channel| channel.process unless channel.closing? }
215:       return false if block_given? && !yield(self)
216:       return true
217:     end
process (wait=nil, &block)

The core of the event loop. It processes a single iteration of the event loop. If a block is given, it should return false when the processing should abort, which causes process to return false. Otherwise, process returns true. The session itself is yielded to the block as its only argument.

If wait is nil (the default), this method will block until any of the monitored IO objects are ready to be read from or written to. If you want it to not block, you can pass 0, or you can pass any other numeric value to indicate that it should block for no more than that many seconds. Passing 0 is a good way to poll the connection, but if you do it too frequently it can make your CPU quite busy!

This will also cause all active channels to be processed once each (see Net::SSH::Connection::Channel#on_process).

# process multiple Net::SSH connections in parallel
connections = [
  Net::SSH.start("host1", ...),
  Net::SSH.start("host2", ...)

connections.each do |ssh|
  ssh.exec "grep something /in/some/files"

condition = { |s| s.busy? }

loop do
  connections.delete_if { |ssh| !ssh.process(0.1, &condition) }
  break if connections.empty?
[show source]
     # File lib/net/ssh/connection/session.rb, line 196
196:     def process(wait=nil, &block)
197:       return false unless preprocess(&block)
199:       r = listeners.keys
200:       w = { |w2| w2.respond_to?(:pending_write?) && w2.pending_write? }
201:       readers, writers, = Net::SSH::Compat.io_select(r, w, nil, wait)
203:       postprocess(readers, writers)
204:     end
send_global_request (type, *extra, &callback)

Send a global request of the given type. The extra parameters must be even in number, and conform to the same format as described for Net::SSH::Buffer.from. If a callback is not specified, the request will not require a response from the server, otherwise the server is required to respond and indicate whether the request was successful or not. This success or failure is indicated by the callback being invoked, with the first parameter being true or false (success, or failure), and the second being the packet itself.

Generally, Net::SSH will manage global requests that need to be sent (e.g. port forward requests and such are handled in the Net::SSH::Service::Forward class, for instance). However, there may be times when you need to send a global request that isn’t explicitly handled by Net::SSH, and so this method is available to you.

[show source]
     # File lib/net/ssh/connection/session.rb, line 260
260:     def send_global_request(type, *extra, &callback)
261:       info { "sending global request #{type}" }
262:       msg = Buffer.from(:byte, GLOBAL_REQUEST, :string, type.to_s, :bool, !callback.nil?, *extra)
263:       send_message(msg)
264:       pending_requests << callback if callback
265:       self
266:     end
send_message (message)

Enqueues a message to be sent to the server as soon as the socket is available for writing. Most programs will never need to call this, but if you are implementing an extension to the SSH protocol, or if you need to send a packet that Net::SSH does not directly support, you can use this to send it.

ssh.send_message(Buffer.from(:byte, REQUEST_SUCCESS).to_s)
[show source]
     # File lib/net/ssh/connection/session.rb, line 367
367:     def send_message(message)
368:       transport.enqueue_message(message)
369:     end
shutdown! ()

Performs a “hard” shutdown of the connection. In general, this should never be done, but it might be necessary (in a rescue clause, for instance, when the connection needs to close but you don’t know the status of the underlying protocol’s state).

[show source]
     # File lib/net/ssh/connection/session.rb, line 118
118:     def shutdown!
119:       transport.shutdown!
120:     end
stop_listening_to (io)

Removes the given io object from the listeners collection, so that the event loop will no longer monitor it.

[show source]
     # File lib/net/ssh/connection/session.rb, line 411
411:     def stop_listening_to(io)
412:       listeners.delete(io)
413:     end