title: fabric hangs while excuting remote bash script
body: <p>I have a bash script named <code>ssadmin.sh</code>, it manages another script <code>sscounter.sh</code> .
  I am using fabric to excute <code>ssadmin.sh</code>.</p>
  
  <p>Without <code>pty=False</code>:</p>
  
  <pre><code>def ts1():
      with settings(warn_only=True):
          run("chmod 775 %s" % 'ssadmin.sh')
          run("%s start" % 'ssadmin.sh')
  </code></pre>
  
  <p><code>sscounter.sh</code> even can not start, but cmd would not be hanged:</p>
  
  <pre><code>root@ubuntu-1404:~# /mithril/scripts/ss-bash/ssadmin.sh status
  ssserver not running
  sscounter.sh not running
  </code></pre>
  
  <p>with <code>pty=False</code>:</p>
  
  <pre><code>def ts1():
      with settings(warn_only=True):
          run("chmod 775 %s" % 'ssadmin.sh')
          run("%s start" % 'ssadmin.sh', pty=False)
  
  
  
  root@ubuntu-1404:~# /mithril/scripts/ss-bash/ssadmin.sh status
  ssserver not running
  10670 ?        S      0:00 /bin/bash /mithril/scripts/ss-bash/sscounter.sh
  sscounter.sh is running
  </code></pre>
  
  <p>sscounter.sh started, but cmd hangs:</p>
  
  <pre><code>E:\[Sync]\project\walbk\fab&gt;fab ts1
  [192.168.1.181] Executing task 'ts1'
  [192.168.1.181] run: chmod 775 /mithril/scripts/ss-bash/ssadmin.sh
  [192.168.1.181] run: /mithril/scripts/ss-bash/ssadmin.sh start
  [192.168.1.181] out: stdin: is not a tty
  [192.168.1.181] out:  9915 ?        S      0:00 /bin/bash /mithril/scripts/ss-bash/sscounter.sh
  [192.168.1.181] out: sscounter.sh鍚姩涓?..
  [192.168.1.181] out: 10670 ?        S      0:00 /bin/bash /mithril/scripts/ss-bash/sscounter.sh
  [192.168.1.181] out: sscounter.sh宸插惎鍔?
  [192.168.1.181] out:                 (hang at here)
  </code></pre>
  
  <p>1.why fabric hangs?</p>
  
  <p>2.<code>fabric pty description</code>:
  <a href="http://docs.fabfile.org/en/latest/usage/interactivity.html#echoes" rel="nofollow">http://docs.fabfile.org/en/latest/usage/interactivity.html#echoes</a></p>
  
  <p><code>pty is present to echo a user’s stdin</code>, why <code>sscounter.sh</code>wouldn't start when <code>pty=True</code>?</p>