Version 2 of the SSH protocol includes a sub-protocol called the “SSH File Transfer Protocol” (SFTP) that lets you walk the remote directory tree, create and delete directories and files, and copy files back and forth from the local to the remote machine. The capabilities of SFTP are so complex and complete, in fact, that they support not only simple file-copy operations, but can power graphical file browsers and can even let the remote filesystem be mounted locally.
When talking about SFTP commands than is provided by the bare
paramiko documentation for the Python SFTP
client( http://www.lag.net/paramiko/docs/paramiko.SFTPClient-class ) ;
here are the main things to remember when doing SFTP:
chdir()to move around the filesystem and then use paths that are relative to the directory in which you have arrived.
open()method and you get back a file-like object connected to an SSH channel that runs independently of your SFTP channel.
fnmatchmodule provides support for Unix shell-style wildcards, which are not the same as regular expressions.
A very modest example SFTP session is shown in
sftp.py. It does something simple that system
administrators might often need: it connects to the remote system and copies messages log files out of the /var/log directory,
perhaps for scanning or analysis on the local machine.
The functools module is for higher-order functions: functions that act on or return other functions. In general, any callable object can be treated as a function for the purposes of this module, as shown in the
import functools import paramiko class AllowAnythingPolicy(paramiko.MissingHostKeyPolicy): def missing_host_key(self, client, hostname, key): return client = paramiko.SSHClient() client.set_missing_host_key_policy(AllowAnythingPolicy()) client.connect('127.0.0.1', username='test') # password='') def my_callback(filename, bytes_so_far, bytes_total): print 'Transfer of %r is at %d/%d bytes (%.1f%%)' % ( filename, bytes_so_far, bytes_total, 100. * bytes_so_far / bytes_total) sftp = client.open_sftp() sftp.chdir('/var/log') for filename in sorted(sftp.listdir()): if filename.startswith('messages.'): callback_for_filename = functools.partial(my_callback, filename) sftp.get(filename, filename, callback=callback_for_filename) client.close()
Note that, although I made a big deal of talking about how each file that you open with SFTP uses its
own independent channel, the simple
put() convenience functions provided by paramiko—
which are really lightweight wrappers for an
open() followed by a loop that reads and writes—do not
attempt any asynchrony, but instead just block and wait until each whole file has arrived. This means that
the foregoing script calmly transfers one file at a time, producing output that looks something like this:
[email protected]:~/Python_files# python sftp.py Transfer of 'messages.1' is at 32768/128609 bytes (25.5%) Transfer of 'messages.1' is at 65536/128609 bytes (51.0%) Transfer of 'messages.1' is at 98304/128609 bytes (76.4%) Transfer of 'messages.1' is at 128609/128609 bytes (100.0%) Transfer of 'messages.2.gz' is at 32768/40225 bytes (81.5%) Transfer of 'messages.2.gz' is at 40225/40225 bytes (100.0%) Transfer of 'messages.3.gz' is at 28249/28249 bytes (100.0%) Transfer of 'messages.4.gz' is at 32768/71703 bytes (45.7%) Transfer of 'messages.4.gz' is at 65536/71703 bytes (91.4%) Transfer of 'messages.4.gz' is at 71703/71703 bytes (100.0%)