source: trunk/athena/etc/ftpd/ftpd.8c @ 7830

.\" Copyright (c) 1985 Regents of the University of California.
.\" All rights reserved.  The Berkeley software License Agreement
.\" specifies the terms and conditions for redistribution.
.\"
.\"     @(#)ftpd.8c     6.4 (Berkeley) 5/28/86
.\"
.TH FTPD 8C "May 1, 1992"
.UC 5
.SH NAME
ftpd \- DARPA Internet File Transfer Protocol server
.SH SYNOPSIS
.B /etc/athena/ftpd
[
.B \-a
] [
.B \-d
] [
.B \-l
] [
.BR \-t timeout
] [
.BR \-b address
]
.SH DESCRIPTION
.I Ftpd
is the DARPA Internet File Transfer Prototocol
server process.  The server uses the TCP protocol
and listens at the port specified in the ``ftp''
service specification; see
.IR services (5).
.PP
If the
.B \-a
option is specified, Athena enhancements to
.I ftpd
are enabled. See details about Athena enhancements below.
.PP
If the 
.B \-d
option is specified,
debugging information is written to the syslog.
.PP
If the
.B \-l
option is specified,
each ftp session is logged in the syslog.
.PP
The ftp server
will timeout an inactive session after 15 minutes.
If the
.B \-t
option is specified,
the inactivity timeout period will be set to
.IR timeout .
.PP
When the client connected to the 
.I ftpd 
server asks for remote help, the server displays an electronic mail
address to which comments should be directed.  By default, this
address is "ftp-bugs@ATHENA.MIT.EDU".
If the
.B \-b
option is specified, then
.I address
will be used instead.
.PP
The ftp server currently supports the following ftp
requests;  case is not distinguished.
.PP
.nf
.ta \w'Request        'u
\fBRequest      Description\fP
ABOR    abort previous command
ACCT    specify account (ignored)
ALLO    allocate storage (vacuously)
APPE    append to a file
ATCH    attach a filesystem
CDUP    change to parent of current working directory
CWD     change working directory
DELE    delete a file
HELP    give help information
LIST    give list files in a directory (``ls -lg'')
MKD     make a directory
MODE    specify data transfer \fImode\fP
NLST    give name list of files in directory (``ls'')
NOOP    do nothing
PASS    specify password
PASV    prepare for server-to-server transfer
PORT    specify data connection port
PWD     print the current working directory
QUIT    terminate session
RETR    retrieve a file
RMD     remove a directory
RNFR    specify rename-from file name
RNTO    specify rename-to file name
STOR    store a file
STOU    store a file with a unique name
STRU    specify data transfer \fIstructure\fP
TYPE    specify data transfer \fItype\fP
USER    specify user name
XCUP    change to parent of current working directory
XCWD    change working directory
XMKD    make a directory
XPWD    print the current working directory
XRMD    remove a directory
.fi
.PP
The remaining ftp requests specified in Internet RFC 959 are
recognized, but not implemented.
.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.
.PP
.I Ftpd
interprets file names according to the ``globbing''
conventions used by
.IR csh (1).
This allows users to utilize the metacharacters ``*?[]{}~''.
.PP
.I Ftpd
uses the following process for authentication.
.IP 1)
The user name must be in the
.IR Hesiod
data base and have a
.IR Kerberos
principal, or be in the password data base,
.IR /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. (NOTE:
.IR Kerberos
and
.IR Hesiod
functionality is only enabled when
.I ftpd
is invoked with the -a option.)
.IP 2)
The user name must not appear in the file
.IR /etc/ftpusers .
.IP 3)
The user must have a standard shell returned by 
.IR getusershell (3).
.IP 4)
If the user name is ``anonymous'' or ``ftp'', an
anonymous ftp account must be present in the password
file (user ``ftp'').  In this case the user is allowed
to log in by specifying any password (by convention this
is given as the client host's name).
.PP
In the last case, 
.I ftpd
takes special measures to restrict the client's access privileges.
The server performs a 
.IR chroot (2)
command to the home directory of the ``ftp'' user.
In order that system security is not breached, it is recommended
that the ``ftp'' subtree be constructed with care;  the following
rules are recommended.
.IP ~ftp)
Make the home directory owned by ``ftp'' and unwritable by anyone.
.IP ~ftp/bin)
Make this directory owned by the super-user and unwritable by
anyone.  The program
.IR ls (1)
must be present to support the list commands.  This
program should have mode 111.
.IP ~ftp/etc)
Make this directory owned by the super-user and unwritable by
anyone.  The files
.IR passwd (5)
and
.IR group (5)
must be present for the 
.I ls
command to work properly.  These files should be mode 444.
.IP ~ftp/pub)
Make this directory mode 777 and owned by ``ftp''.  Users
should then place files which are to be accessible via the
anonymous account in this directory.
.SH "ENHANCEMENTS FOR THE ATHENA ENVIRONMENT"
This
.I ftpd
has been enhanced to work properly in the Athena environment, when
invoked with the -a option.

It does a full login of the user much as
.IR login,
including
.IR Kerberos
authentication, attaching of the user's home directory, and entry into
the password file and
.IR /etc/utmp.
It also honors
.IR /etc/nologin,
.IR /etc/nocreate,
.IR /etc/noremote,
.IR /etc/noattach,
and
.IR /etc/nocrack.
.PP
Upon closing of the ftp connection (or HUP and TERM signals),
.I ftpd
destroys the
.IR Kerberos
tickets it obtained (if any), and runs
.I fsid
-u on the user's home directory.
.PP
In addition, this
.I ftpd
also supports an attach command, ATCH.  Arguments following ATCH
are passed directly to
.IR attach.
If
.IR Kerberos
authentication was not obtained,
.I ftpd
adds a "-n" to the attach command line, so that attaches don't
attempt to use
.IR Kerberos
authentication.  Note that this may be overridden by specifying
"-y" on the command line.
.PP
In clients that don't support the attach command, but do support
the
.IR quote
command, a command line such as
.PP
        quote atch bitbucket
.PP
may be used to attach filesystems.
.SH "SEE ALSO"
ftp(1C), getusershell(3), syslogd(8), kerberos(1), attach(1), unlog(1)
.SH BUGS
The anonymous account is inherently dangerous and should
avoided when possible.
.PP
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.
.PP
Some
.IR ftp
clients truncate the password the user types to eight characters.
Since
.IR Kerberos
passwords don't have this limitation, if the user's password is
longer than eight characters the user may not be able to log in.
This is not, strictly speaking, a bug in
.I ftpd,
but
.I ftpd
will be the first suspect, so this is a good place to document
the problem.
.PP
.I Ftpd
adds an entry to
.IR utmp
to show the user as logged in.  Since it doesn't require a tty,
it places "ftpN" (where N is an ftp line number) in its line entry in
.IR utmp.
This causes unpatched versions of
.I finger
to break trying to stat /dev/ftpN, which doesn't exist. A gross
workaround for this (short of fixing finger) is to link
/dev/ftp{0,1,2,3...} to /dev/null.