set timezone on Ubuntu

Ubuntu server uses UTC for the default timezone, this blog will guide
you if you wanna change the default timezone

first select your timezone interactively by using 'tzselect', you may
need 'sudo'
after that, we wanna make the change permanently

sudo cp /usr/share/zoneinfo/Asia/Shanghai /etc/localtime

finally we change 'UTC=yes' into 'UTC=no' in the file located at
'/etc/default/rcS'

now you have it done! do a 'date' for sure

Rails 3 issue: 'Content-Length' field not exist in HTTP head when using 'send_data' method

I found this issue in one of my Rails 3 app, here is a simple demo:

class AnyController < ApplicationController
  def any_action
    send_data [SOME-BINARY-DATA]
  end
end

when browser make any request to this controller, Rails 3 app will
REMOVE your 'Content-Length' field of the HTTP response header, even
you add content-length in the logic code explicitly

To fix this, we could add a Rack middleware and plug it in to the app,
in your #{Rails.root}/config/application.rb file, find code like below:

module XX
    class Application < Rails::Application
        config.middleware.use "HttpHeaderFix" # add this line

then create a file named 'http_header_fix.rb' at #{Rails.root}/middleware

class HttpHeaderFix
  def initialize(app)
    @app = app
  end

  def call(env)
    status, headers, response = @app.call(env)
    if headers["Content-Type"] == "application/octet-stream"
      if headers["Content-Length"].blank?
        if response.respond_to? :length
          length = response.length
        elsif response.respond_to? :count
          length = response.count
        elsif response.respond_to? :size
          length = response.size
        elsif response.respond_to? :body
          length = response.body.length
        else
          raise "unknown response: #{response.class}"
        end
        headers["Content-Length"] = length.to_s
      end
    end
    [status, headers, response]
  end
end

OK, there you go!!

Setup ssh proxy under linux

First setup OpenSSH
check your /etc/shells file if it contains a line '/sbin/nologin'

Then you want just add your SSH account like this:

useradd -M -s /sbin/nologin -n username

some version of Linux may like this:

useradd -s /sbin/nologin username

and even the 'nologin' shell is located at '/usr/sbin/nologin' in some
Linux version

Now, you have a SSH server & account setup

Recommended web browser plugins for SSH proxy:
Firefox users checkout autoproxy:
https://addons.mozilla.org/en-US/firefox/addon/autoproxy/
Chrome users checkout Switchy!:
https://chrome.google.com/webstore/detail/caehdcpeofiiigpdhbabniblemipncjj