1.0 - Introduction

python -m pyftpdlib.ftpserver

Customizing ftpd for basic tasks like adding users or deciding where log file should be placed is mostly simply editing variables. This is basically like learning how to edit a common unix ftpd.conf file and doesn't really require Python knowledge. Customizing ftpd more deeply requires a python script which imports pyftpdlib to be written separately. An example about how this could be done are the scripts contained in the demo directory.

1.4 - Documentation

http://code.google.com/p/pyftpdlib/ is the primary source for all information about the project including Install instructions, Tutorial, RFCs Compliance paper, Wikis and the Bug Tracker.

1.5 - Mailing lists

There are a number of mailing lists for pyftpdlib:

Name	E-mail	Web Interface	Description
pyftpdlib	pyftpdlib@googlegroups.com	topics	This is intended for end user support.
pyftpdlib-commit	pyftpdlib-commits@googlegroups.com	topics	This list receives all change notifications for code in the Subversion repository. Unless you're a pyftpdlib developer you will probably not be interested in it.
pyftpdlib-issues	pyftpdlib-issues@googlegroups.com	topics	This list receives all change notifications from the Bug Tracker. Unless you are involved into pyftpdlib development you will probably not find this useful.

1.6 - Bug reporting

Bug reports should be made via Google Code Issue Tracker. Patches should be attached to the appropriate bug and not mailed directly to the mailing lists or any given team member.

2.0 - Installing and compatibility

2.1 - How do I install pyftpdlib?

If you are not new to Python you probably don't need that, otherwise follow the instructions.

2.2 - Which Python versions are compatible?

Python 2.3 and higher.

2.3 - Which one is recommended?

Python 2.4 or higher because of the newer collection.deque object which provides better performances for file transfers.

2.4 - What about Python 3.x?

Python 3.0 is still in beta version thus not yet covered. A porting of pyftpdlib to Python 3k is in plan, anyway.

2.5 - On which platforms can pyftpdlib be used?

pyftpdlib should work on any platform where select() or poll() system calls are available and on any Python implementation which refers to CPython 2.3 or superior (e.g CPython 2.6 or PythonCE 2.5). The development team has mainly tested it under various Linux, Windows, OS X and FreeBSD systems. For FreeBSD is also available a pre-compiled package maintained by Li-Wen Hsu <lwhsu@freebsd.org>. Other Python implementation like PythonCE are known to work with pyftpdlib and every new version is usually tested against it. pyftpdlib currently does not work on Jython since the latest Jython release refers to CPython 2.2.x serie.

3.0 - Usage

3.1 - Why do I get socket.error "Permission denied" error on ftpd starting?

Probably because you're on a unix system and you're trying to start ftpd as an unprivileged user. ftpserver.py binds on port 21 by default and only super-user account (e.g. root) could bind sockets on such ports. If you want to bind ftpd as non-privileged user you should set a port higher than 1024.

3.2 - How can I prevent the server version from being displayed?

Just override and modify banner attribute of FTPHandler class.

3.3 - Can control upload/download ratios?

Yes. throttled_ftpd.py script included in the demo directory implements bandwidth throttling capabilities for both upload and download.

3.4 - Are there ways to limit connections?

FTPServer class comes with two overridable attributes defaulting to zero (no limit): max_cons, which sets a limit for maximum simultaneous connection to handle by ftpd and max_cons_per_ip which set a limit for connections from the same IP address. Overriding these variables is always recommended to avoid DoS attacks.

3.5 - I'm behind a NAT / gateway

When behind a NAT a ftp server needs to replace the IP local address displayed in PASV replies and instead use the public address of the NAT to allow client to connect. By overriding masquerade_address attribute of FTPHandler class you will force pyftpdlib to do such replacement. However, one big problem still exists. The passive FTP connections will use ports from 1024 and up, which means that you must forward all ports 1024-65535 from the NAT to the FTP server! And you have to allow many (possibly) dangerous ports in your firewalling rules! To resolve this, simply override passive_ports attribute of FTPHandler class to control what ports proftpd will use for its passive data transfers. Value expected by passive_ports attribute is a list of integers (e.g. range(60000, 65535)) indicating which ports will be used for initializing the passive data channel.

3.6.1 - What is FXP?

FXP is part of the name of a popular Windows FTP client: http://www.flashfxp.com. This client has made the name "FXP" commonly used as a synonym for site-to-site FTP transfers, for transferring a file between two remote FTP servers without the transfer going through the client's host. Sometimes "FXP" is referred to as a protocol; in fact, it is not. The site-to-site transfer capability was deliberately designed into RFC-959. More info can be found here: http://www.proftpd.org/docs/howto/FXP.html.

3.6.2 - Does pyftpdlib support FXP?

Yes. It is disabled by default for security reasons (see RFC-2257 and FTP bounce attack description) but in case you want to enable it just set to True the permit_foreign_addresses attribute of FTPHandler class.

4.0 - Implementation

4.1 - Globbing / STAT command implementation

Globbing is a common Unix shell mechanism for expanding wildcard patterns to match multiple filenames. When an argument is provided to the STAT command, ftpd should return directory listing over the command channel. RFC-959 does not explicitly mention globbing; this means that FTP servers are not required to support globbing in order to be compliant. However, many FTP servers do support globbing as a measure of convenience for FTP clients and users. In order to search for and match the given globbing expression, the code has to search (possibly) many directories, examine each contained filename, and build a list of matching files in memory. Since this operation can be quite intensive, both CPU- and memory-wise, pyftpdlib does not support globbing.

4.2 - ASCII transfers / SIZE command implementation

Properly handling the SIZE command when TYPE ASCII is used would require to scan the entire file to perform the ASCII translation logic (file.read().replace(os.linesep, '\r\n')) and then calculating the len of such data which may be different than the actual size of the file on the server. Considering that calculating such result could be very resource-intensive it could be easy for a malicious client to try a DoS attack, thus pyftpdlib do not perform the ASCII translation. However, clients in general should not be resuming downloads in ASCII mode. Resuming downloads in binary mode is the recommended way as specified in RFC-3659.

4.3.1 - IPv6 support

Starting from version 0.4.0 pyftpdlib supports IPv6 (RFC-2428). If you use IPv6 and want your FTP daemon to do so just pass a valid IPv6 address to the FTPServer class constructor. Example:

>>> from pyftpdlib import ftpserver
>>> address = ("::1", 21)  # listen on localhost, port 21
>>> ftpd = ftpserver.FTPServer(address, ftpserver.FTPHandler)
>>> ftpd.serve_forever()
Serving FTP on ::1:21

4.3.2 - How do I install IPv6 support on my system?

If you want to install IPv6 support on Linux run "modprobe ipv6", then "ifconfig". This should display the loopback adapter, with the address "::1". You should then be able to listen the server on that address, and connect to it.

On Windows (XP SP2 and higher) run "netsh int ipv6 install". Again, you should be able to use IPv6 loopback afterwards.

4.4 - Can pyftpdlib be integrated with "real" users existing on the system?

Yes. By using the proper system dependent authorizer pyftpdlib can look into the system account database to authenticate users. Starting from version 0.4.0 the DummyAuthorizer class provides two new methods: impersonate_user() and terminate_impersonation(). System dependent authorizers subclassing the dummy authorizer can assume the id of real users by overriding them as necessary. Every time the FTP server is going to access the filesystem (e.g. for creating or renaming a file) it will temporarily impersonate the currently logged on user, execute the filesystem call and then switch back to the user who originally started the server. Example UNIX and Windows FTP servers contained in the demo directory implement both real user impersonation and authentication against the system users database.

4.5 - SSL/TLS support

SSL/TLS support including AUTH, ADAT, PROT, PBSZ, CCC, MIC, CONF and ENC commands is a feature defined in RFC-2228. There is no official support for SSL/TLS within the current code tree. The new Python 2.6 release finally grants full SSL support so we hope we'll be able to implement the feature. Contributors willing to to provide a patch are greatly appreciated.