File: ftpd.8

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linux-ftpd 0.17-34
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.\"
.\" Copyright (c) 1985, 1988, 1991, 1993
.\"	The Regents of the University of California.  All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in the
.\"    documentation and/or other materials provided with the distribution.
.\" 3. All advertising materials mentioning features or use of this software
.\"    must display the following acknowledgement:
.\"	This product includes software developed by the University of
.\"	California, Berkeley and its contributors.
.\" 4. Neither the name of the University nor the names of its contributors
.\"    may be used to endorse or promote products derived from this software
.\"    without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.\"     @(#)ftpd.8	8.2 (Berkeley) 4/19/94
.\"	NetBSD: ftpd.8,v 1.8 1996/01/14 20:55:23 thorpej Exp
.\"	OpenBSD: ftpd.8,v 1.9 1996/12/03 03:07:16 deraadt Exp
.\"	OpenBSD: ftpd.8,v 1.12 1997/05/01 14:45:36 deraadt Exp
.\"	OpenBSD: ftpd.8,v 1.22 1999/07/09 13:35:50 aaron Exp
.\"     $Id: ftpd.8,v 1.17 2000/07/30 23:56:57 dholland Exp $
.\"
.Dd September 14, 1999
.Dt FTPD 8
.Os "Linux NetKit (0.17)"
.Sh NAME
.Nm ftpd
.Nd
Internet File Transfer Protocol server
.Sh SYNOPSIS
.Nm ftpd
.Op Fl AdDhlMnPSU
.Op Fl T Ar maxtimeout
.Op Fl t Ar timeout
.Op Fl u Ar mask
.Sh DESCRIPTION
.Nm Ftpd
is the
Internet File Transfer Protocol
server process.  The server uses the
.Tn TCP
protocol
and listens at the port specified in the
.Dq ftp
service specification; see
.Xr services 5 .
.Pp
Available options:
.Bl -tag -width Ds
.It Fl 4
Use IPv4 addressing only. The default is to offer service for both families, IPv6 and IPv4.
.It Fl 6
Only provide IPv6 addressing capability.
.It Fl A
Permit only anonymous ftp connections or accounts listed in
.Pa /etc/ftpchroot.
Other connection attempts are refused.  This option is no longer effective if
PAM is enabled.  Please refer to the README file for instructions to doing
this with PAM.
.It Fl d
Debugging information is written to the syslog using LOG_FTP.
.It Fl D
With this option set,
.Nm ftpd
will detach and become a daemon, accepting connections on the FTP port and
forking child processes to handle them. This has lower overhead than
starting
.Nm ftpd
from
.Xr inetd 8
and is thus useful on busy servers to reduce load.
.It Fl h
The server will use data ports in the high port range for passive connections.
This range is defined by the
.Ev IPPORT_HIFIRSTAUTO
and
.Ev IPPORT_HILASTAUTO
defines in <netinet/in.h>.  In
.Ox
they are set to 49152 and 65535 respectively.
.It Fl l
Each successful and failed
.Xr ftp 1
session is logged using syslog with a facility of LOG_FTP.
If this option is specified twice, the retrieve (get), store (put), append,
delete, make directory, remove directory and rename operations and
their filename arguments are also logged.
.It Fl M
Enables multihomed mode.  Instead of simply using
.Pa ~ftp
for anonymous transfers, a directory matching the fully qualified name of
the IP number the client connected to, and located inside
.Pa ~ftp
is used instead.
.It Fl n
Use numeric IP addresses in logs instead of doing hostname lookup.
.It Fl P
Permit illegal port numbers or addresses for PORT command initiated connects.
By default
.Xr ftpd 8
violates the RFC and thus constrains the PORT command to non-reserved ports
and requires it use the same source address as the connection came from.
This prevents the "FTP bounce attack" against services on both the local
machine and other local machines.
.It Fl S
With this option set,
.Nm ftpd
logs all anonymous transfers to the file
.Pa /var/log/ftpd
when this file exists.
.It Fl U
Each concurrent
.Xr ftp 1
session is logged to the file
.Pa /var/run/utmp ,
making them visible to commands such as
.Xr who 1 .
This option at present is unsupporte and will always silently fail.
.It Fl T
A client may also request a different timeout period;
the maximum period allowed may be set to
.Ar timeout
seconds with the
.Fl T
option.
The default limit is 2 hours.
.It Fl t
The inactivity timeout period is set to
.Ar timeout
seconds (the default is 15 minutes).
.It Fl u
Change the default umask from 027 to
.Ar mask .
.El
.Pp
The file
.Pa /etc/nologin
can be used to disable ftp access.
If the file exists,
.Nm
displays it and exits.
If the file
.Pa /etc/ftpwelcome
exists,
.Nm
prints it before issuing the
.Dq ready
message.
If the file
.Pa /etc/motd
exists,
.Nm
prints it after a successful login.  If the file
.Pa .message
exists in a directory,
.Nm
prints it when that directory is entered.
.Pp
The ftp server currently supports the following ftp requests.
The case of the requests is ignored.
.Bl -column "Request" -offset indent
.It Request Ta "Description"
.It ABOR Ta "abort previous command"
.It ACCT Ta "specify account (ignored)"
.It ALLO Ta "allocate storage (vacuously)"
.It APPE Ta "append to a file"
.It CDUP Ta "change to parent of current working directory"
.It CWD Ta "change working directory"
.It DELE Ta "delete a file"
.It EPRT Ta "specify data connection port, either IPv4 or IPv6"
.It EPSV Ta "ask for a server port for fetching data"
.It HELP Ta "give help information"
.It LIST Ta "give list files in a directory" Pq Dq Li "ls -lgA"
.It MKD Ta "make a directory"
.It MDTM Ta "show last modification time of file"
.It MODE Ta "specify data transfer" Em mode
.It NLST Ta "give name list of files in directory"
.It NOOP Ta "do nothing"
.It PASS Ta "specify password"
.It PASV Ta "prepare for server-to-server transfer"
.It PORT Ta "specify data connection port"
.It PWD Ta "print the current working directory"
.It QUIT Ta "terminate session"
.It REST Ta "restart incomplete transfer"
.It RETR Ta "retrieve a file"
.It RMD Ta "remove a directory"
.It RNFR Ta "specify rename-from file name"
.It RNTO Ta "specify rename-to file name"
.It SITE Ta "non-standard commands (see next section)"
.It SIZE Ta "return size of file"
.It STAT Ta "return status of server"
.It STOR Ta "store a file"
.It STOU Ta "store a file with a unique name"
.It STRU Ta "specify data transfer" Em structure
.It SYST Ta "show operating system type of server system"
.It TYPE Ta "specify data transfer" Em type
.It USER Ta "specify user name"
.It XCUP Ta "change to parent of current working directory (deprecated)"
.It XCWD Ta "change working directory (deprecated)"
.It XMKD Ta "make a directory (deprecated)"
.It XPWD Ta "print the current working directory (deprecated)"
.It XRMD Ta "remove a directory (deprecated)"
.El
.Pp
The following non-standard or
.Tn UNIX
specific commands are supported
by the
SITE request.
.Pp
.Bl -column Request -offset indent
.It Sy Request Ta Sy Description
.It UMASK Ta change umask, e.g. ``SITE UMASK 002''
.It IDLE Ta set idle-timer, e.g. ``SITE IDLE 60''
.It CHMOD Ta change mode of a file, e.g. ``SITE CHMOD 755 filename''
.It HELP Ta give help information.
.El
.Pp
The remaining ftp requests specified in Internet RFC 959
are
recognized, but not implemented.
MDTM and SIZE are not specified in RFC 959, but will appear in the
next updated FTP RFC.
.Pp
The ftp server will abort an active file transfer only when the
ABOR
command is preceded by a Telnet "Interrupt Process" (IP)
signal and a Telnet "Synch" signal in the command Telnet stream,
as described in Internet RFC 959.
If a
STAT
command is received during a data transfer, preceded by a Telnet IP
and Synch, transfer status will be returned.
.Pp
.Nm Ftpd
interprets file names according to the
.Dq globbing
conventions used by
.Xr csh 1 .
This allows users to utilize the metacharacters
.Dq Li \&*?[]{}~ .
.Pp
.Nm Ftpd
authenticates users according to five rules.
.Pp
.Bl -enum -offset indent
.It
The login name must be in the password data base,
.\" .Pa /etc/pwd.db ,
.Pa /etc/passwd ,
and not have a null password.
In this case a password must be provided by the client before any
file operations may be performed.
If the user has an S/Key key, the response from a successful USER
command will include an S/Key challenge. The client may choose to respond
with a PASS command giving either a standard password or an S/Key
one-time password. The server will automatically determine which type of
password it has been given and attempt to authenticate accordingly. See
.Xr skey 1
for more information on S/Key authentication. S/Key is a Trademark of
Bellcore.
.It
The login name must not appear in the file
.Pa /etc/ftpusers .
.It
The user must have a standard shell returned by
.Xr getusershell 3 .
.It
If the user name appears in the file
.Pa /etc/ftpchroot
the session's root will be changed to the user's login directory by
.Xr chroot 2
as for an
.Dq anonymous
or
.Dq ftp
account (see next item).  However, the user must still supply a password.
This feature is intended as a compromise between a fully anonymous account
and a fully privileged account.  The account should also be set up as for an
anonymous account.
.It
If the user name is
.Dq anonymous
or
.Dq ftp ,
an
anonymous ftp account must be present in the password
file (user
.Dq ftp ) .
In this case the user is allowed
to log in by specifying any password (by convention an email address for
the user should be used as the password).
.El
.Pp
In the last case,
.Nm ftpd
takes special measures to restrict the client's access privileges.
The server performs a
.Xr chroot 2
to the home directory of the
.Dq ftp
user.
In order that system security is not breached, it is recommended
that the
.Dq ftp
subtree be constructed with care, following these rules:
.Bl -tag -width "~ftp/pub" -offset indent
.It Pa ~ftp
Make the home directory owned by
.Dq root
and unwritable by anyone (mode 555).
.It Pa ~ftp/bin
Make this directory owned by
.Dq root
and unwritable by anyone (mode 511).
.\"This directory is optional unless you have commands you wish
.\"the anonymous ftp user to be able to run (the
.\".Xr ls 1
.\"command exists as a builtin).
.\"  -- not in the Linux port (yet?)
This directory is required, and should contain at least a statically
linked copy of
.Xr ls 1.
Any programs in this directory should be mode 111 (executable only).
.It Pa ~ftp/etc
Make this directory owned by
.Dq root
and unwritable by anyone (mode 511).
The files 
.\" pwd.db (see
.\" .Xr pwd_mkdb 8 )
.Xr passwd 5
and
.Xr group 5
must be present for the
.Xr ls
command to be able to produce owner names rather than numbers.
The password field in
.\" .Xr pwd.db
.Pa passwd
is not used, and should not contain real passwords.
The file
.Pa motd ,
if present, will be printed after a successful login.
These files should be mode 444.
.It Pa ~ftp/lib
Make this directory owned by
.Dq root
and unwritable by anyone (mode 511).
The libraries
.Xr ld-linux.so.2
and
.Xr libc.so.6
(or whatever your
.Xr ls
command is linked to)
must be present.
In order to read 
.Xr passwd 5
and
.Xr group 5 ,
the library
.Xr libnss_files.so.2
is also needed.
Note that if you're using a 2.2.* or later Linux kernel,
.Xr ld-linux.so.2
must be executable as well as readable (555).  All other files should be mode
444.
.It Pa ~ftp/pub
Make this directory mode 555 and owned by
.Dq root .
This is traditionally where publically accessible files are
stored for download.
.El
.Sh FILES
.Bl -tag -width /etc/ftpwelcome -compact
.It Pa /etc/ftpusers
List of unwelcome/restricted users.
.It Pa /etc/ftpchroot
List of normal users who should be chroot'd.
.It Pa /etc/ftpwelcome
Welcome notice.
.It Pa /etc/motd
Welcome notice after login.
.It Pa /etc/nologin
Displayed and access refused.
.It Pa /var/run/utmp
List of users on the system.
.It Pa /var/log/ftpd
Log file for anonymous transfers.
.El
.Sh SEE ALSO
.Xr ftp 1 ,
.Xr skey 1 ,
.Xr who 1 ,
.Xr getusershell 3 ,
.Xr ftpusers 5 ,
.Xr syslogd 8
.Sh BUGS
The server must run as the super-user
to create sockets with privileged port numbers.  It maintains
an effective user ID of the logged in user, reverting to
the super-user only when binding addresses to sockets.  The
possible security holes have been extensively
scrutinized, but are possibly incomplete.
.Sh HISTORY
The
.Nm
command appeared in
.Bx 4.2 .