872 lines
22 KiB
Groff
872 lines
22 KiB
Groff
.\" $NetBSD: ftpd.8,v 1.85 2009/05/01 10:53:27 wiz Exp $
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.\"
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.\" Copyright (c) 1997-2008 The NetBSD Foundation, Inc.
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.\" All rights reserved.
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.\"
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.\" This code is derived from software contributed to The NetBSD Foundation
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.\" by Luke Mewburn.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
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.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
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.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
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.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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.\" POSSIBILITY OF SUCH DAMAGE.
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.\"
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.\" Copyright (c) 1985, 1988, 1991, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)ftpd.8 8.2 (Berkeley) 4/19/94
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.\"
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.Dd May 1, 2009
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.Dt FTPD 8
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.Os
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.Sh NAME
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.Nm ftpd
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.Nd
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Internet File Transfer Protocol server
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.Sh SYNOPSIS
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.Nm
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.Op Fl 46DdHlnQqrsUuWwX
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.Op Fl a Ar anondir
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.Op Fl C Ar user Ns Op @ Ns Ar host
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.Op Fl c Ar confdir
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.Op Fl e Ar emailaddr
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.Op Fl h Ar hostname
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.Op Fl L Ar xferlogfile
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.Op Fl P Ar dataport
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.Op Fl V Ar version
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.Sh DESCRIPTION
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.Nm
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is the Internet File Transfer Protocol server process.
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The server uses the
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.Tn TCP
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protocol and listens at the port specified in the
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.Dq ftp
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service specification; see
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.Xr services 5 .
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.Pp
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Available options:
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.Bl -tag -width Ds
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.It Fl 4
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When
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.Fl D
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is specified, bind to IPv4 addresses only.
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.It Fl 6
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When
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.Fl D
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is specified, bind to IPv6 addresses only.
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.It Fl a Ar anondir
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Define
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.Ar anondir
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as the directory to
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.Xr chroot 2
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into for anonymous logins.
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Default is the home directory for the ftp user.
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This can also be specified with the
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.Xr ftpd.conf 5
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.Sy chroot
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directive.
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.It Fl C Ar user Ns Op @ Ns Ar host
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Check whether
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.Ar user
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.Po
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as if connecting from
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.Ar host ,
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if provided
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.Pc
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would be granted access under
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the restrictions given in
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.Xr ftpusers 5 ,
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and exit without attempting a connection.
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.Nm
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exits with an exit code of 0 if access would be granted, or 1 otherwise.
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This can be useful for testing configurations.
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.It Fl c Ar confdir
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Change the root directory of the configuration files from
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.Dq Pa /etc
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to
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.Ar confdir .
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This changes the directory for the following files:
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.Pa /etc/ftpchroot ,
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.Pa /etc/ftpusers ,
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.Pa /etc/ftpwelcome ,
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.Pa /etc/motd ,
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and the file specified by the
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.Xr ftpd.conf 5
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.Sy limit
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directive.
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.It Fl D
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Run as daemon.
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.Nm
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will listen on the default FTP port for incoming connections
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and fork a child for each connection.
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This is lower overhead than starting
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.Nm
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from
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.Xr inetd 8
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and thus might be useful on busy servers to reduce load.
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.It Fl d
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Debugging information is written to the syslog using a facility of
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.Dv LOG_FTP .
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.It Fl e Ar emailaddr
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Use
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.Ar emailaddr
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for the
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.Dq "\&%E"
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escape sequence (see
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.Sx Display file escape sequences )
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.It Fl H
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Equivalent to
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.Do
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-h
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`hostname`
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.Dc .
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.It Fl h Ar hostname
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Explicitly set the hostname to advertise as to
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.Ar hostname .
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The default is the hostname associated with the IP address that
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.Nm
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is listening on.
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This ability (with or without
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.Fl h ) ,
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in conjunction with
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.Fl c Ar confdir ,
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is useful when configuring
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.Sq virtual
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.Tn FTP
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servers, each listening on separate addresses as separate names.
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Refer to
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.Xr inetd.conf 5
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for more information on starting services to listen on specific IP addresses.
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.It Fl L Ar xferlogfile
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Log
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.Tn wu-ftpd
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style
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.Sq xferlog
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entries to
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.Ar xferlogfile .
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.It Fl l
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Each successful and failed
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.Tn FTP
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session is logged using syslog with a facility of
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.Dv LOG_FTP .
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If this option is specified more than once, the retrieve (get), store (put),
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append, delete, make directory, remove directory and rename operations and
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their file name arguments are also logged.
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.It Fl n
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Don't attempt translation of IP addresses to hostnames.
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.It Fl P Ar dataport
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Use
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.Ar dataport
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as the data port, overriding the default of using the port one less
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that the port
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.Nm
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is listening on.
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.It Fl Q
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Disable the use of pid files for keeping track of the number of logged-in
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users per class.
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This may reduce the load on heavily loaded
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.Tn FTP
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servers.
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.It Fl q
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Enable the use of pid files for keeping track of the number of logged-in
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users per class.
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This is the default.
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.It Fl r
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Permanently drop root privileges once the user is logged in.
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The use of this option may result in the server using a port other
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than the (listening-port - 1) for
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.Sy PORT
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style commands, which is contrary to the
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.Cm RFC 959
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specification, but in practice very few clients rely upon this behaviour.
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See
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.Sx SECURITY CONSIDERATIONS
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below for more details.
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.It Fl s
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Require a secure authentication mechanism like Kerberos or S/Key to be used.
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.It Fl U
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Don't log each concurrent
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.Tn FTP
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session to
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.Pa /var/run/utmp .
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This is the default.
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.It Fl u
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Log each concurrent
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.Tn FTP
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session to
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.Pa /var/run/utmp ,
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making them visible to commands such as
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.Xr who 1 .
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.It Fl V Ar version
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Use
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.Ar version
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as the version to advertise in the login banner and in the output of
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.Sy STAT
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and
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.Sy SYST
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instead of the default version information.
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If
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.Ar version
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is empty or
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.Sq -
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then don't display any version information.
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.It Fl W
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Don't log each
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.Tn FTP
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session to
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.Pa /var/log/wtmp .
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.It Fl w
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Log each
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.Tn FTP
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session to
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.Pa /var/log/wtmp ,
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making them visible to commands such as
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.Xr last 1 .
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This is the default.
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.It Fl X
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Log
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.Tn wu-ftpd
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style
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.Sq xferlog
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entries to the syslog, prefixed with
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.Dq "xferlog:\ " ,
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using a facility of
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.Dv LOG_FTP .
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These syslog entries can be converted to a
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.Tn wu-ftpd
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style
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.Pa xferlog
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file suitable for input into a third-party log analysis tool with a command
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similar to:
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.Dl "sed -ne 's/^.*xferlog: //p' /var/log/xferlog \*[Gt] wuxferlog"
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.El
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.Pp
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The file
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.Pa /etc/nologin
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can be used to disable
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.Tn FTP
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access.
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If the file exists,
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.Nm
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displays it and exits.
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If the file
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.Pa /etc/ftpwelcome
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exists,
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.Nm
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prints it before issuing the
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.Dq ready
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message.
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If the file
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.Pa /etc/motd
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exists (under the chroot directory if applicable),
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.Nm
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prints it after a successful login.
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This may be changed with the
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.Xr ftpd.conf 5
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directive
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.Sy motd .
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.Pp
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The
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.Nm
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server currently supports the following
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.Tn FTP
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requests.
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The case of the requests is ignored.
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.Bl -column "Request" "Description" -offset indent
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.It Sy Request Ta Sy Description
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.It ABOR Ta "abort previous command"
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.It ACCT Ta "specify account (ignored)"
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.It ALLO Ta "allocate storage (vacuously)"
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.It APPE Ta "append to a file"
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.It CDUP Ta "change to parent of current working directory"
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.It CWD Ta "change working directory"
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.It DELE Ta "delete a file"
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.It EPSV Ta "prepare for server-to-server transfer"
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.It EPRT Ta "specify data connection port"
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.It FEAT Ta "list extra features that are not defined in" Cm "RFC 959"
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.It HELP Ta "give help information"
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.It LIST Ta "give list files in a directory" Pq Dq Li "ls -lA"
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.It LPSV Ta "prepare for server-to-server transfer"
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.It LPRT Ta "specify data connection port"
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.It MLSD Ta "list contents of directory in a machine-processable form"
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.It MLST Ta "show a pathname in a machine-processable form"
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.It MKD Ta "make a directory"
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.It MDTM Ta "show last modification time of file"
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.It MODE Ta "specify data transfer" Em mode
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.It NLST Ta "give name list of files in directory"
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.It NOOP Ta "do nothing"
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.It OPTS Ta "define persistent options for a given command"
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.It PASS Ta "specify password"
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.It PASV Ta "prepare for server-to-server transfer"
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.It PORT Ta "specify data connection port"
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.It PWD Ta "print the current working directory"
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.It QUIT Ta "terminate session"
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.It REST Ta "restart incomplete transfer"
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.It RETR Ta "retrieve a file"
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.It RMD Ta "remove a directory"
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.It RNFR Ta "specify rename-from file name"
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.It RNTO Ta "specify rename-to file name"
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.It SITE Ta "non-standard commands (see next section)"
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.It SIZE Ta "return size of file"
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.It STAT Ta "return status of server"
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.It STOR Ta "store a file"
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.It STOU Ta "store a file with a unique name"
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.It STRU Ta "specify data transfer" Em structure
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.It SYST Ta "show operating system type of server system"
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.It TYPE Ta "specify data transfer" Em type
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.It USER Ta "specify user name"
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.It XCUP Ta "change to parent of current working directory (deprecated)"
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.It XCWD Ta "change working directory (deprecated)"
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.It XMKD Ta "make a directory (deprecated)"
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.It XPWD Ta "print the current working directory (deprecated)"
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.It XRMD Ta "remove a directory (deprecated)"
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.El
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.Pp
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The following non-standard or
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.Ux
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specific commands are supported by the SITE request.
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.Pp
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.Bl -column Request Description -offset indent
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.It Sy Request Ta Sy Description
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.It CHMOD Ta "change mode of a file, e.g. ``SITE CHMOD 755 filename''"
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.It HELP Ta "give help information."
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.It IDLE Ta "set idle-timer, e.g. ``SITE IDLE 60''"
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.It RATEGET Ta "set maximum get rate throttle in bytes/second, e.g. ``SITE RATEGET 5k''"
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.It RATEPUT Ta "set maximum put rate throttle in bytes/second, e.g. ``SITE RATEPUT 5k''"
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.It UMASK Ta "change umask, e.g. ``SITE UMASK 002''"
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.El
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.Pp
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The following
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.Tn FTP
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requests (as specified in
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.Cm RFC 959
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and
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.Cm RFC 2228 )
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are recognized, but are not implemented:
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.Sy ACCT ,
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.Sy ADAT ,
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.Sy AUTH ,
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.Sy CCC ,
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.Sy CONF ,
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.Sy ENC ,
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.Sy MIC ,
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.Sy PBSZ ,
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.Sy PROT ,
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.Sy REIN ,
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and
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.Sy SMNT .
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.Pp
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The
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.Nm
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server will abort an active file transfer only when the
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.Sy ABOR
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command is preceded by a Telnet "Interrupt Process" (IP)
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signal and a Telnet "Synch" signal in the command Telnet stream,
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as described in Internet
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.Cm RFC 959 .
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If a
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.Sy STAT
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command is received during a data transfer, preceded by a Telnet IP
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and Synch, transfer status will be returned.
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.Pp
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.Nm
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interprets file names according to the
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.Dq globbing
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conventions used by
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.Xr csh 1 .
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This allows users to use the metacharacters
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.Dq Li \&*?[]{}~ .
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.Ss User authentication
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.Nm
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authenticates users according to five rules.
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.Pp
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.Bl -enum -offset indent
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.It
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The login name must be in the password data base,
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.Xr passwd 5 ,
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and not have a null password.
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In this case a password must be provided by the client before any
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file operations may be performed.
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If the user has an S/Key key, the response from a successful
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.Sy USER
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command will include an S/Key challenge.
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The client may choose to respond with a
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.Sy PASS
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command giving either
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a standard password or an S/Key one-time password.
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The server will automatically determine which type of password it
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has been given and attempt to authenticate accordingly.
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See
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.Xr skey 1
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for more information on S/Key authentication.
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S/Key is a Trademark of Bellcore.
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.It
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The login name must be allowed based on the information in
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.Xr ftpusers 5 .
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.It
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The user must have a standard shell returned by
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.Xr getusershell 3 .
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If the user's shell field in the password database is empty, the
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shell is assumed to be
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.Pa /bin/sh .
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As per
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.Xr shells 5 ,
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the user's shell must be listed with full path in
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.Pa /etc/shells .
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.It
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If directed by the file
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.Xr ftpchroot 5
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the session's root directory will be changed by
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.Xr chroot 2
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to the directory specified in the
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.Xr ftpd.conf 5
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.Sy chroot
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directive (if set),
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or to the home directory of the user.
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This facility may also be triggered by enabling the boolean
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.Sy ftp-chroot
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in
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.Xr login.conf 5 .
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However, the user must still supply a password.
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This feature is intended as a compromise between a fully anonymous account
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and a fully privileged account.
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The account should also be set up as for an anonymous account.
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.It
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If the user name is
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.Dq anonymous
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or
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.Dq ftp ,
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an
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anonymous
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.Tn FTP
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account must be present in the password
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file (user
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.Dq ftp ) .
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In this case the user is allowed
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to log in by specifying any password (by convention an email address for
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the user should be used as the password).
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.Pp
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The server performs a
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.Xr chroot 2
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to the directory specified in the
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.Xr ftpd.conf 5
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.Sy chroot
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directive (if set),
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the
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.Fl a Ar anondir
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directory (if set),
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or to the home directory of the
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.Dq ftp
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user.
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.Pp
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The server then performs a
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.Xr chdir 2
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to the directory specified in the
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.Xr ftpd.conf 5
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.Sy homedir
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directive (if set), otherwise to
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.Pa / .
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.Pp
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If other restrictions are required (such as disabling of certain
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commands and the setting of a specific umask), then appropriate
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entries in
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.Xr ftpd.conf 5
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are required.
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.Pp
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If the first character of the password supplied by an anonymous user
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is
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.Dq - ,
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then the verbose messages displayed at login and upon a
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.Sy CWD
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command are suppressed.
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.El
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.Ss Display file escape sequences
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|
When
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.Nm
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|
displays various files back to the client (such as
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.Pa /etc/ftpwelcome
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and
|
|
.Pa /etc/motd ) ,
|
|
various escape strings are replaced with information pertinent
|
|
to the current connection.
|
|
.Pp
|
|
The supported escape strings are:
|
|
.Bl -tag -width "Escape" -offset indent -compact
|
|
.It Sy "Escape"
|
|
.Sy Description
|
|
.It "\&%c"
|
|
Class name.
|
|
.It "\&%C"
|
|
Current working directory.
|
|
.It "\&%E"
|
|
Email address given with
|
|
.Fl e .
|
|
.It "\&%L"
|
|
Local hostname.
|
|
.It "\&%M"
|
|
Maximum number of users for this class.
|
|
Displays
|
|
.Dq unlimited
|
|
if there's no limit.
|
|
.It "\&%N"
|
|
Current number of users for this class.
|
|
.It "\&%R"
|
|
Remote hostname.
|
|
.It "\&%s"
|
|
If the result of the most recent
|
|
.Dq "\&%M"
|
|
or
|
|
.Dq "\&%N"
|
|
was not
|
|
.Dq Li 1 ,
|
|
print an
|
|
.Dq s .
|
|
.It "\&%S"
|
|
If the result of the most recent
|
|
.Dq "\&%M"
|
|
or
|
|
.Dq "\&%N"
|
|
was not
|
|
.Dq Li 1 ,
|
|
print an
|
|
.Dq S .
|
|
.It "\&%T"
|
|
Current time.
|
|
.It "\&%U"
|
|
User name.
|
|
.It "\&%\&%"
|
|
A
|
|
.Dq \&%
|
|
character.
|
|
.El
|
|
.Ss Setting up a restricted ftp subtree
|
|
In order that system security is not breached, it is recommended
|
|
that the
|
|
subtrees for the
|
|
.Dq ftp
|
|
and
|
|
.Dq chroot
|
|
accounts be constructed with care, following these rules
|
|
(replace
|
|
.Dq ftp
|
|
in the following directory names
|
|
with the appropriate account name for
|
|
.Sq chroot
|
|
users):
|
|
.Bl -tag -width "~ftp/incoming" -offset indent
|
|
.It Pa ~ftp
|
|
Make the home directory owned by
|
|
.Dq root
|
|
and unwritable by anyone.
|
|
.It Pa ~ftp/bin
|
|
Make this directory owned by
|
|
.Dq root
|
|
and unwritable by anyone (mode 555).
|
|
Generally any conversion commands should be installed
|
|
here (mode 111).
|
|
.It Pa ~ftp/etc
|
|
Make this directory owned by
|
|
.Dq root
|
|
and unwritable by anyone (mode 555).
|
|
The files
|
|
.Pa pwd.db
|
|
(see
|
|
.Xr passwd 5 )
|
|
and
|
|
.Pa group
|
|
(see
|
|
.Xr group 5 )
|
|
must be present for the
|
|
.Sy LIST
|
|
command to be able to display owner and group names instead of numbers.
|
|
The password field in
|
|
.Xr passwd 5
|
|
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/pub
|
|
This directory and the subdirectories beneath it should be owned
|
|
by the users and groups responsible for placing files in them,
|
|
and be writable only by them (mode 755 or 775).
|
|
They should
|
|
.Em not
|
|
be owned or writable by ftp or its group.
|
|
.It Pa ~ftp/incoming
|
|
This directory is where anonymous users place files they upload.
|
|
The owners should be the user
|
|
.Dq ftp
|
|
and an appropriate group.
|
|
Members of this group will be the only users with access to these
|
|
files after they have been uploaded; these should be people who
|
|
know how to deal with them appropriately.
|
|
If you wish anonymous
|
|
.Tn FTP
|
|
users to be able to see the names of the
|
|
files in this directory the permissions should be 770, otherwise
|
|
they should be 370.
|
|
.Pp
|
|
The following
|
|
.Xr ftpd.conf 5
|
|
directives should be used:
|
|
.Dl "modify guest off"
|
|
.Dl "umask guest 0707"
|
|
.Dl "upload guest on"
|
|
.Pp
|
|
This will result in anonymous users being able to upload files to this
|
|
directory, but they will not be able to download them, delete them, or
|
|
overwrite them, due to the umask and disabling of the commands mentioned
|
|
above.
|
|
.It Pa ~ftp/tmp
|
|
This directory is used to create temporary files which contain
|
|
the error messages generated by a conversion or
|
|
.Sy LIST
|
|
command.
|
|
The owner should be the user
|
|
.Dq ftp .
|
|
The permissions should be 300.
|
|
.Pp
|
|
If you don't enable conversion commands, or don't want anonymous users
|
|
uploading files here (see
|
|
.Pa ~ftp/incoming
|
|
above), then don't create this directory.
|
|
However, error messages from conversion or
|
|
.Sy LIST
|
|
commands won't be returned to the user.
|
|
(This is the traditional behaviour.)
|
|
Note that the
|
|
.Xr ftpd.conf 5
|
|
directive
|
|
.Sy upload
|
|
can be used to prevent users uploading here.
|
|
.El
|
|
.Pp
|
|
To set up "ftp-only" accounts that provide only
|
|
.Tn FTP ,
|
|
but no valid shell
|
|
login, you can copy/link
|
|
.Pa /sbin/nologin
|
|
to
|
|
.Pa /sbin/ftplogin ,
|
|
and enter
|
|
.Pa /sbin/ftplogin
|
|
to
|
|
.Pa /etc/shells
|
|
to allow logging-in via
|
|
.Tn FTP
|
|
into the accounts, which must have
|
|
.Pa /sbin/ftplogin
|
|
as login shell.
|
|
.Sh FILES
|
|
.Bl -tag -width /etc/ftpwelcome -compact
|
|
.It Pa /etc/ftpchroot
|
|
List of normal users whose root directory should be changed via
|
|
.Xr chroot 2 .
|
|
.It Pa /etc/ftpd.conf
|
|
Configure file conversions and other settings.
|
|
.It Pa /etc/ftpusers
|
|
List of unwelcome/restricted users.
|
|
.It Pa /etc/ftpwelcome
|
|
Welcome notice before login.
|
|
.It Pa /etc/motd
|
|
Welcome notice after login.
|
|
.It Pa /etc/nologin
|
|
If it exists, displayed and access is refused.
|
|
.It Pa /var/run/ftpd.pids-CLASS
|
|
State file of logged-in processes for the
|
|
.Nm
|
|
class
|
|
.Sq CLASS .
|
|
.It Pa /var/run/utmp
|
|
List of logged-in users on the system.
|
|
.It Pa /var/log/wtmp
|
|
Login history database.
|
|
.El
|
|
.Sh SEE ALSO
|
|
.Xr ftp 1 ,
|
|
.Xr skey 1 ,
|
|
.Xr who 1 ,
|
|
.Xr getusershell 3 ,
|
|
.Xr ftpchroot 5 ,
|
|
.Xr ftpd.conf 5 ,
|
|
.Xr ftpusers 5 ,
|
|
.Xr login.conf 5 ,
|
|
.Xr syslogd 8
|
|
.Sh STANDARDS
|
|
.Nm
|
|
recognizes all commands in
|
|
.Cm RFC 959 ,
|
|
follows the guidelines in
|
|
.Cm RFC 1123 ,
|
|
recognizes all commands in
|
|
.Cm RFC 2228
|
|
(although they are not supported yet),
|
|
and supports the extensions from
|
|
.Cm RFC 2389 ,
|
|
.Cm RFC 2428 ,
|
|
and
|
|
.Cm RFC 3659 .
|
|
.Sh HISTORY
|
|
The
|
|
.Nm
|
|
command appeared in
|
|
.Bx 4.2 .
|
|
.Pp
|
|
Various features such as the
|
|
.Xr ftpd.conf 5
|
|
functionality,
|
|
.Cm RFC 2389 ,
|
|
and
|
|
.Cm RFC 3659
|
|
support was implemented in
|
|
.Nx 1.3
|
|
and later releases by Luke Mewburn.
|
|
.Sh BUGS
|
|
The server must run as the super-user to create sockets with
|
|
privileged port numbers (i.e, those less than
|
|
.Dv IPPORT_RESERVED ,
|
|
which is 1024).
|
|
If
|
|
.Nm
|
|
is listening on a privileged port
|
|
it maintains an effective user id of the logged in user, reverting
|
|
to the super-user only when binding addresses to privileged sockets.
|
|
The
|
|
.Fl r
|
|
option can be used to override this behaviour and force privileges to
|
|
be permanently revoked; see
|
|
.Sx SECURITY CONSIDERATIONS
|
|
below for more details.
|
|
.Pp
|
|
.Nm
|
|
may have trouble handling connections from scoped IPv6 addresses, or
|
|
IPv4 mapped addresses
|
|
.Po
|
|
IPv4 connection on
|
|
.Dv AF_INET6
|
|
socket
|
|
.Pc .
|
|
For the latter case, running two daemons,
|
|
one for IPv4 and one for IPv6, will avoid the problem.
|
|
.Sh SECURITY CONSIDERATIONS
|
|
.Cm RFC 959
|
|
provides no restrictions on the
|
|
.Sy PORT
|
|
command, and this can lead to security problems, as
|
|
.Nm
|
|
can be fooled into connecting to any service on any host.
|
|
With the
|
|
.Dq checkportcmd
|
|
feature of the
|
|
.Xr ftpd.conf 5 ,
|
|
.Sy PORT
|
|
commands with different host addresses, or TCP ports lower than
|
|
.Dv IPPORT_RESERVED
|
|
will be rejected.
|
|
This also prevents
|
|
.Sq third-party proxy ftp
|
|
from working.
|
|
Use of this option is
|
|
.Em strongly
|
|
recommended, and enabled by default.
|
|
.Pp
|
|
By default
|
|
.Nm
|
|
uses a port that is one less than the port it is listening on to
|
|
communicate back to the client for the
|
|
.Sy EPRT ,
|
|
.Sy LPRT ,
|
|
and
|
|
.Sy PORT
|
|
commands, unless overridden with
|
|
.Fl P Ar dataport .
|
|
As the default port for
|
|
.Nm
|
|
(21) is a privileged port below
|
|
.Dv IPPORT_RESERVED ,
|
|
.Nm
|
|
retains the ability to switch back to root privileges to bind these
|
|
ports.
|
|
In order to increase security by reducing the potential for a bug in
|
|
.Nm
|
|
providing a remote root compromise,
|
|
.Nm
|
|
will permanently drop root privileges if one of the following is true:
|
|
.Bl -enum -offset indent
|
|
.It
|
|
.Nm
|
|
is running on a port greater than
|
|
.Dv IPPORT_RESERVED
|
|
and the user has logged in as a
|
|
.Sq guest
|
|
or
|
|
.Sq chroot
|
|
user.
|
|
.It
|
|
.Nm
|
|
was invoked with
|
|
.Fl r .
|
|
.El
|
|
.Pp
|
|
Don't create
|
|
.Pa ~ftp/tmp
|
|
if you don't want anonymous users to upload files there.
|
|
That directory is only necessary if you want to display the error
|
|
messages of conversion commands to the user.
|
|
Note that if uploads are disabled with the
|
|
.Xr ftpd.conf 5
|
|
directive
|
|
.Sy upload ,
|
|
then this directory cannot be abused by the user in this way, so it
|
|
should be safe to create.
|
|
.Pp
|
|
To avoid possible denial-of-service attacks,
|
|
.Sy SIZE
|
|
requests against files larger than 10240 bytes will be denied if
|
|
the current transfer
|
|
.Sy TYPE
|
|
is
|
|
.Sq Li A
|
|
(ASCII).
|