Net::SFTP connection not closing

Question

I have a Ruby on Rails (Rails 3.2.14 and ruby 1.9.3) application that uploads 2 files to a remote SFTP server. The SFTP code is:

require 'net/sftp'
Rails.logger.info("Creating SFTP connection")
uri = URI.parse('sftp://'+ host)
Net::SFTP.start(uri.host,'user', :password=>'password',:port=>port) do |sftp|
    Rails.logger.info("SFTP Connection created, uploading files.")
    sftp.upload!("public/file1.txt", "./file1.txt")
    Rails.logger.info("First file uploaded.")
    sftp.upload!("file2.txt", "./file2.txt")
    Rails.logger.info("Both files uploaded, terminating connection.")
end
Rails.logger.info("Connection terminated.")

Both files are uploading properly to the remote server, but the connection doesn't seem to close. I keep getting an error when I execute this function and on analyzing my console, I see that the "Both files uploaded, terminating connection." logger message is running, but nothing after that. I've tried using

sftp.close(:handle)
sftp.close!(:handle)
#and
sftp.close_connection()

but none of them are working. Any idea on why this is happening and how I can rectify it? I'm running this through a single instance Engine Yard cloud server.

EDIT These are the last few lines in my log: Creating SFTP connection SFTP Connection created, uploading files. First file uploaded. Both files uploaded, terminating connection.

After that, nothing. When viewing my log with the 'tail -f' command, the log goes up to that last line, and the app redirects to the internal server error page.

The issue is not about connection not getting closed. It closes automatically when the block ends. What is the error that you keep getting? — techvineet, Sep 10 '13 at 12:12
I get an internal server error that directs me to the 500.html file in my public folder. Is there any way I can verify exactly what this error is or what's causing the error? — adnann, Sep 10 '13 at 12:29
The log terminates after Rails.logger.info("Both files uploaded, terminating connection."). This is the last message the log shows. After that, the error occurs, I'm redirected to the server error page and the log doesn't show anything. Considering that the log doesn't move on to Rails.logger.info("Connection terminated."), I assumed that it's a connection termination issue... — adnann, Sep 10 '13 at 12:37
You have post to the controller & action where you are doing this. — techvineet, Sep 10 '13 at 12:41
I don't quite understand what you're saying. I just tried to figure out the exact error by implementing exception handling, but even that didn't work. Whatever the error is, it completely skips the catch block and goes straight to the internal server error page. — adnann, Sep 11 '13 at 04:58
There is log file in your Rails.root/log/production.log. You can see the exact error there. If you are not sure post the last few lines here. — techvineet, Sep 11 '13 at 05:25

score 16 · Accepted Answer · answered Apr 20 '16 at 18:32

Short answer

Net::SFTP.start('host', 'user', password: 'pass', port: 22) do |sftp|

  # Do stuff

end

is equivalent to :

session = Net::SSH.start('host', 'user', password: 'pass', port: 22)
sftp = Net::SFTP::Session.new(session)
sftp.connect!

# Do stuff

sftp.close_channel unless sftp.nil?
session.close unless session.nil?

Better answer

For people that couldn't find a way to actually close the connection, without using auto-closing blocks, here is how I you can achieve this :

require 'net/ssh'
require 'net/sftp'

begin

  # Instance SSH/SFTP session :
  session = Net::SSH.start('host', 'user', password: 'pass', port: 22)
  sftp = Net::SFTP::Session.new(session)

  # Always good to timeout :
  Timeout.timeout(10) do
    sftp.connect! # Establish connection

    # Do stuff

  end

rescue Timeout::Error => e

  # Do some custom logging
  puts e.message 

ensure

  # Close SSH/SFTP session
  sftp.close_channel unless sftp.nil? # Close SFTP
  session.close unless session.nil? # Then SSH

  # If you really really really wanna make sure it's closed,
  # and raise after 10 seconds delay
  Timeout.timeout(10) do
    sleep 1 until (sftp.nil? or sftp.closed?) and (session.nil? or session.closed?)
  end

end

If you don't close the connection before performing some other task, you might sometimes experience errors like this in rails for instance :

IOError (not opened for reading) # Not closed when rendering controller action
ActionView::Template::Error (not opened for reading) # Not closed when rendering template

Really appreciated the breakdown here of what the Net:SFTP:start do structure is equivalent to. — Ethel Evans, Sep 08 '16 at 22:30
While this is a really good breakdown. People need to be warned about `Timeout` and it's potential implications. https://jvns.ca/blog/2015/11/27/why-rubys-timeout-is-dangerous-and-thread-dot-raise-is-terrifying/ — TheRealMrCrowley, Aug 16 '17 at 18:54
@TheRealMrCrowley : Thanks, I didn't know about that. Luckily, I always used the explicit `rescue Timeout::Error` in the apps I have in production :) — Ghis, Aug 17 '17 at 14:06
Note that you don't need to manually create a `Net::SSH` session. If you are using `Net::SFTP.start`, you can still close the SSH session using `sftp.session.close` (first do `sftp.close_channel`). — nyi, Apr 07 '22 at 14:32

score 3 · Answer 2 · answered Sep 11 '13 at 09:21

I don't know why, but rewriting the code to include 'net/ssh' and creating the sftp connection explicitly through SSH worked!

require 'net/ssh'
require 'net/sftp'
#upload a file or directory to the remote host
Rails.logger.info("Creating SFTP connection")
session=Net::SSH.start('host','user', :password=>'password',:port=>port)
sftp=Net::SFTP::Session.new(session).connect!
Rails.logger.info("SFTP Connection created, uploading files.")
sftp.upload!("file1.txt", "./file1.txt")
Rails.logger.info("First file uploaded.")
sftp.upload!("file2.txt", "./file2.txt")
Rails.logger.info("Both files uploaded, terminating connection.")
Rails.logger.info("Connection terminated.")

Perhaps someone can shed some light on why this one worked and the other didn't.

I had the same issue, and this work around was the only thing that resolved it. — Doug, Nov 04 '14 at 20:19

score 3 · Answer 3 · answered Jul 28 '20 at 22:57

3

The auto-closing block will be able to close if you send an EOF at the end of your block:

Net::SFTP.start(host, user, port: port, password: password) do |sftp|
    # ... do your things
    sftp.channel.eof!
end

answered Jul 28 '20 at 22:57

JellicleCat

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One of the servers I was integrating with had this problem after sometime running smoothly and closing the channel fixed it. I'm still not sure why this happened to a single server though – lsdr Jul 17 '23 at 18:55

Net::SFTP connection not closing

3 Answers3

Short answer

Better answer