python - EOF when using pexpect and pxssh

Question

I'm trying to run the code in the Interacting with SSH Through Pexpect and Brute Forcing SSH Passwords with Pxssh sections from Chapter 2 of Violent Python. Using both child.expect() and pxssh I get similar EOF errors.

Running these commands from the Python console:

import pexpect
connStr = "ssh [email protected]"
child = pexpect.spawn(connStr)
ret = child.expect([pexpect.TIMEOUT, ssh_newkey, "[P|p]assword:"])

I get this output:

Traceback (most recent call last):
  File "<input>", line 1, in <module>
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/pexpect.py", li
ne 1316, in expect
    return self.expect_list(compiled_pattern_list, timeout, searchwindowsize)
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/pexpect.py", li
ne 1330, in expect_list
    return self.expect_loop(searcher_re(pattern_list), timeout, searchwindowsize)
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/pexpect.py", li
ne 1401, in expect_loop
    raise EOF (str(e) + '
' + str(self))
EOF: End Of File (EOF) in read_nonblocking(). Empty string style platform.
<pexpect.spawn object at 0x10180c550>
version: 2.4 ($Revision: 516 $)
command: /usr/bin/ssh
args: ['/usr/bin/ssh', '[email protected]']
searcher: searcher_re:
    0: TIMEOUT
    1: re.compile("Are you sure you want to continue connecting")
    2: re.compile("[P|p]assword:")
buffer (last 100 chars): 
before (last 100 chars): 
after: <class 'pexpect.EOF'>
match: None
match_index: None
exitstatus: 255 
flag_eof: True
pid: 12122
child_fd: 4
closed: False
timeout: 30
delimiter: <class 'pexpect.EOF'>
logfile: None
logfile_read: None
logfile_send: None
maxread: 2000
ignorecase: False
searchwindowsize: None
delaybeforesend: 0.05
delayafterclose: 0.1
delayafterterminate: 0.1

And running these commands, using pxssh:

import pxssh
s = pxssh.pxssh()
s.login("127.0.0.1", "root", "1234")

I get this output:

Traceback (most recent call last):
  File "<input>", line 1, in <module>
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/pxssh.py", line
 196, in login
    i = self.expect(["(?i)are you sure you want to continue connecting", original_prompt, "(?i)(?:pas
sword)|(?:passphrase for key)", "(?i)permission denied", "(?i)terminal type", TIMEOUT, "(?i)connectio
n closed by remote host"], timeout=login_timeout)
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/pexpect.py", li
ne 1316, in expect
    return self.expect_list(compiled_pattern_list, timeout, searchwindowsize)
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/pexpect.py", li
ne 1330, in expect_list
    return self.expect_loop(searcher_re(pattern_list), timeout, searchwindowsize)
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/pexpect.py", li
ne 1401, in expect_loop
    raise EOF (str(e) + '
' + str(self))
EOF: End Of File (EOF) in read_nonblocking(). Empty string style platform.
<pxssh.pxssh object at 0x1016bff90>
version: 2.4 ($Revision: 516 $)
command: /usr/bin/ssh
args: ['/usr/bin/ssh', '-q', '-l', 'root', '127.0.0.1']
searcher: searcher_re:
    0: re.compile("(?i)are you sure you want to continue connecting")
    1: re.compile("[#$]")
    2: re.compile("(?i)(?:password)|(?:passphrase for key)")
    3: re.compile("(?i)permission denied")
    4: re.compile("(?i)terminal type")
    5: TIMEOUT
    6: re.compile("(?i)connection closed by remote host")
buffer (last 100 chars): 
before (last 100 chars): 
after: <class 'pexpect.EOF'>
match: None
match_index: None
exitstatus: None
flag_eof: True
pid: 12136
child_fd: 3
closed: False
timeout: 30
delimiter: <class 'pexpect.EOF'>
logfile: None
logfile_read: None
logfile_send: None
maxread: 2000
ignorecase: False
searchwindowsize: None
delaybeforesend: 0.05
delayafterclose: 0.1
delayafterterminate: 0.1

I get similar results when I substitute 127.0.0.1 with other hosts and try different username/password combinations.

The pexpect documentation suggests using expect(pexpect.EOF) to avoid generating the EOF exception. Indeed, when I do the following:

connStr = "ssh [email protected]"
child = pexpect.spawn(connStr)
print child.expect(pexpect.EOF)

The result is 0.

But the following questions remain:

1. I'm confused by the book's syntax: child.expect([pexpect.TIMEOUT, ssh_newkey, "[P|p]assword:"]). Why are we passing a list to expect()? What is this list supposed to contain?
2. How do I make use of expect(pexpect.EOF), as the documentation instructs, when using pxssh?
3. Why does the code in the book not work properly? Has something changed in the pexpect library since the book's publication? Is it because I am on OS X?

I have Python 2.7 and pexpect 2.4 running on Mac OS X 10.8.4.

Answer 1

Regarding #2: Expecting EOF is a red herring here. You -don't- expect EOF on login, you expect a password prompt on login. pxssh kicks that error when it gets back EOF on login from ssh without getting a password prompt. This can happen because it's using ssh -q to not get warnings, and you're getting a warning from ssh. Take the ssh options it is using and run them yourself without the q:

/usr/bin/ssh -l root 127.0.0.1

In my case, I can get this error message when ssh is kicking out a known hosts violation due to the machine I am connecting to having its identity changed.