pxssh — Extends pexpect.spawn to specialize setting up SSH connections.

This class extends pexpect.spawn to specialize setting up SSH connections. This adds methods for login, logout, and expecting the shell prompt.

$Id: pxssh.py 513 2008-02-09 18:26:13Z noah $

exception pxssh.ExceptionPxssh(value)

Raised for pxssh exceptions.

class pxssh.pxssh(timeout=30, maxread=2000, searchwindowsize=None, logfile=None, cwd=None, env=None)

This class extends pexpect.spawn to specialize setting up SSH connections. This adds methods for login, logout, and expecting the shell prompt. It does various tricky things to handle many situations in the SSH login process. For example, if the session is your first login, then pxssh automatically accepts the remote certificate; or if you have public key authentication setup then pxssh won’t wait for the password prompt.

pxssh uses the shell prompt to synchronize output from the remote host. In order to make this more robust it sets the shell prompt to something more unique than just $ or #. This should work on most Borne/Bash or Csh style shells.

Example that runs a few commands on a remote server and prints the result:

import pxssh
import getpass
try:                                                            
    s = pxssh.pxssh()
    hostname = raw_input('hostname: ')
    username = raw_input('username: ')
    password = getpass.getpass('password: ')
    s.login (hostname, username, password)
    s.sendline ('uptime')  # run a command
    s.prompt()             # match the prompt
    print s.before         # print everything before the prompt.
    s.sendline ('ls -l')
    s.prompt()
    print s.before
    s.sendline ('df')
    s.prompt()
    print s.before
    s.logout()
except pxssh.ExceptionPxssh, e:
    print "pxssh failed on login."
    print str(e)

Note that if you have ssh-agent running while doing development with pxssh then this can lead to a lot of confusion. Many X display managers (xdm, gdm, kdm, etc.) will automatically start a GUI agent. You may see a GUI dialog box popup asking for a password during development. You should turn off any key agents during testing. The ‘force_password’ attribute will turn off public key authentication. This will only work if the remote SSH server is configured to allow password logins. Example of using ‘force_password’ attribute:

s = pxssh.pxssh()
s.force_password = True
hostname = raw_input('hostname: ')
username = raw_input('username: ')
password = getpass.getpass('password: ')
s.login (hostname, username, password)

levenshtein_distance(a, b)

This calculates the Levenshtein distance between a and b.

login(server, username, password='', terminal_type='ansi', original_prompt='[#$]', login_timeout=10, port=None, auto_prompt_reset=True)

This logs the user into the given server. It uses the ‘original_prompt’ to try to find the prompt right after login. When it finds the prompt it immediately tries to reset the prompt to something more easily matched. The default ‘original_prompt’ is very optimistic and is easily fooled. It’s more reliable to try to match the original prompt as exactly as possible to prevent false matches by server strings such as the “Message Of The Day”. On many systems you can disable the MOTD on the remote server by creating a zero-length file called “~/.hushlogin” on the remote server. If a prompt cannot be found then this will not necessarily cause the login to fail. In the case of a timeout when looking for the prompt we assume that the original prompt was so weird that we could not match it, so we use a few tricks to guess when we have reached the prompt. Then we hope for the best and blindly try to reset the prompt to something more unique. If that fails then login() raises an ExceptionPxssh exception.

In some situations it is not possible or desirable to reset the original prompt. In this case, set ‘auto_prompt_reset’ to False to inhibit setting the prompt to the UNIQUE_PROMPT. Remember that pxssh uses a unique prompt in the prompt() method. If the original prompt is not reset then this will disable the prompt() method unless you manually set the PROMPT attribute.

logout()

This sends exit to the remote shell. If there are stopped jobs then this automatically sends exit twice.

prompt(timeout=20)

This matches the shell prompt. This is little more than a short-cut to the expect() method. This returns True if the shell prompt was matched. This returns False if there was a timeout. Note that if you called login() with auto_prompt_reset set to False then you should have manually set the PROMPT attribute to a regex pattern for matching the prompt.

set_unique_prompt()

This sets the remote prompt to something more unique than # or $. This makes it easier for the prompt() method to match the shell prompt unambiguously. This method is called automatically by the login() method, but you may want to call it manually if you somehow reset the shell prompt. For example, if you ‘su’ to a different user then you will need to manually reset the prompt. This sends shell commands to the remote host to set the prompt, so this assumes the remote host is ready to receive commands.

Alternatively, you may use your own prompt pattern. Just set the PROMPT attribute to a regular expression that matches it. In this case you should call login() with auto_prompt_reset=False; then set the PROMPT attribute. After that the prompt() method will try to match your prompt pattern.

sync_original_prompt()

This attempts to find the prompt. Basically, press enter and record the response; press enter again and record the response; if the two responses are similar then assume we are at the original prompt. This is a slow function. It can take over 10 seconds.