path: root/libexec/ftpd/ftpd.8

.\"	$OpenBSD: ftpd.8,v 1.55 2002/11/15 19:52:15 millert Exp $
.\"	$NetBSD: ftpd.8,v 1.8 1996/01/14 20:55:23 thorpej Exp $
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.\"     @(#)ftpd.8	8.2 (Berkeley) 4/19/94
.\"
.Dd June 18, 1996
.Dt FTPD 8
.Os
.Sh NAME
.Nm ftpd
.Nd Internet File Transfer Protocol server
.Sh SYNOPSIS
.Nm ftpd
.Op Fl AdDlMnPSU46
.Op Fl T Ar maxtimeout
.Op Fl t Ar timeout
.Op Fl u Ar mask
.Sh DESCRIPTION
.Nm
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
The options are as follows:
.Bl -tag -width Ds
.It Fl A
Permit only anonymous ftp connections, accounts listed in
.Pa /etc/ftpchroot
or users in a login class with the
.Dq ftp-chroot
variable set (see below).
Other connection attempts are refused.
.It Fl d
Debugging information is written to the syslog using LOG_FTP.
.It Fl D
With this option set,
.Nm
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
from
.Xr inetd 8
and is thus useful on busy servers to reduce load.
.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
Do not permit anonymous ftp logins.
Normally they are permitted.
.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
logs all anonymous downloads 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 .
.It Fl 4
When
.Fl D
is specified, forces
.Nm
to use IPv4 addresses only.
.It Fl 6
When
.Fl D
is specified, forces
.Nm
to use IPv6 addresses only.
.It Fl T Ar maxtimeout
A client may also request a different timeout period;
the maximum period allowed may be set to
.Ar maxtimeout
seconds with the
.Fl T
option.
The default limit is 2 hours.
.It Fl t Ar timeout
The inactivity timeout period is set to
.Ar timeout
seconds (the default is 15 minutes).
.It Fl u Ar mask
Force the umask to
.Ar mask .
instead of the default specified in
.Pa /etc/login.conf
(usually 022).
Also disallows chmod.
.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 welcome file exists
.Pa ( /etc/motd
by default),
.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 Sy Request Ta Sy 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 EPSV Ta "prepare for server-to-server transfer"
.It EPRT Ta "specify data connection port"
.It HELP Ta "give help information"
.It LIST Ta "give list files in a directory" Pq Dq Li "ls -lgA"
.It LPSV Ta "prepare for server-to-server transfer"
.It LPRT Ta "specify data connection port"
.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, not valid after login"
.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
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
authenticates users by using the service and type of
.Ar ftp ,
as defined in the
.Pa /etc/login.conf
file (see
.Xr login.conf 5 ) .
An authentication style
may be specified by appending with a colon (
.Do
:
.Dc
)
following the authentication style, i.e.
.Dq joe:skey .
The allowed authentication styles for
.Nm
may be explicitly specified by the
.Dq auth-ftp
entry in
.Pa /etc/login.conf .
.Pp
.Nm
authenticates users according to five rules.
.Pp
.Bl -enum -offset indent
.It
The login name must be in the password database and not have a null password.
In this case a password must be provided by the client before any
file operations may be performed.
.It
The login name must not appear in the file
.Pa /etc/ftpusers .
.It
The user must have a standard shell as described by
.Xr shells 5 .
.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
Once a user is authenticated the user must be approved by any approval
script defined (see
.Xr login.conf 5 ) .
If a valid approval script (by either :approve=...: or :approve-ftp=...:
for the user's class) is defined then it is run and must exit with a 0
(success) status.
When
.Nm
is running under the
.Fl D
flag (and debugging is not turned on) then the approval script will be
called with at least the following variables specified via the
.Fl v
option (see
.Xr login.conf 5 )
to the approve script:
.Bl -column "Variable" -offset indent
.It Sy Variable Ta Sy Description
.It FTPD_HOST Ta "The server's (virtual) hostname"
.El
.Pp
For example (the line is broken to fit the page):
.sp
.Bd -ragged -offset indent
.Pa /usr/libexec/auth/approve_ftpd Fl v
FTPD_HOST=ftp.mycompany.com \\
.Dl Ar username Ar class Ar service
.Ed
.Pp
When the user logs in to the anonymous ftp account,
.Nm
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).
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 )
and
.Xr group 5
must be present for the
.Xr ls 1
command to be able to produce owner names rather than numbers.
The password field in
.Pa pwd.db
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
Make this directory mode 555 and owned by
.Dq root .
This is traditionally where publicly accessible files are
stored for download.
.El
.Pp
If logging to the
.Pa /var/log/ftpd
file is enabled, information will be written in the following format:
.Pp
.Bl -tag -width XXXXXXXXXXXXXX -offset indent -compact
.It time
The time and date of the download, in
.Xr ctime 3
format.
.It elapsed time
The elapsed time, in seconds.
.It remote host
The remote host (or IP number).
.It bytes
The number of bytes transferred.
.It path
The full path (relative the ftp chroot space) of the file transferred.
.It type
The type of transfer; either
.Dq a
for ASCII or
.Dq b
for binary.
.It unused
Unused field containing a
.Dq * ,
for compatibility.
.It unused
Unused field containing a
.Dq o ,
for compatibility.
.It user type
The type of user, either
.Dq a
for anonymous, or
.Dq r
for a real user (should always be anonymous).
.It name
Either a system login name or the value given for
.Dq email address
if an anonymous user.
.It unused
Unused field, containing a
.Dq 0 ,
for compatibility.
.It real name
The system login name if the connection is not anonymous, or a
.Dq *
if it is.
.It virtual host
The virtual host that the connection was made to.
.El
.Pp
Although fields exist for logging information on real users, this file is
only used for anonymous downloads.
Unused fields exist only for compatibility with other
.Nm
implementations.
.Sh LOGIN.CONF VARIABLES
The
.Nm
daemon uses the following ftp specific parameters:
.Bl -tag -width ftp-chroot
.It Pa auth-ftp
The list of authentication types available to this class.
See
.Xr login.conf 5 .
.It Pa ftp-chroot
A boolean value.
If set, users in this class will be automatically chrooted to
the user's login directory.
.It Pa ftp-dir
A path to a directory.
This value overrides the login directory for users in this class.
A leading tilde
.Pq Ql ~
in
.Pa ftp-dir
will be expanded to the user's home directory based on the
contents of the password database.
.It Pa welcome
The path of the file containing the welcome message.
If this variable is not set,
.Pa /etc/motd
is used.
.El
.Sh PORT ALLOCATION
For passive mode data connections, 
.Nm
will listen to a random high tcp port.
The interval of ports used are configurable using
.Xr sysctl 8 
variables
.Li net.inet.ip.porthifirst
and
.Li net.inet.ip.porthilast .
.Sh FILES
.Bl -tag -width /var/run/ftpd.pid -compact
.It Pa /etc/ftpchroot
list of normal users who should be chrooted
.It Pa /etc/ftpusers
list of unwelcome/restricted users
.It Pa /etc/ftpwelcome
welcome notice
.It Pa /etc/login.conf
authentication styles
.It Pa /etc/motd
printed after a successful login
.It Pa /etc/nologin
displayed and access refused
.It Pa /var/log/ftpd
log file for anonymous downloads
.It Pa /var/run/ftpd.pid
process ID if running in daemon mode
.It Pa /var/run/utmp
list of users on the system
.El
.Sh SEE ALSO
.Xr ftp 1 ,
.Xr skey 1 ,
.Xr who 1 ,
.Xr chroot 2 ,
.Xr login.conf 5 ,
.Xr shells 5 ,
.Xr inetd 8 ,
.Xr syslogd 8 ,
.Xr ftp-proxy 8
.Sh HISTORY
The
.Nm
command appeared in
.Bx 4.2 .
.Sh BUGS
The server must run as the superuser to create sockets with
privileged port numbers.
It maintains
an effective user ID of the logged in user, reverting to
the superuser only when binding addresses to sockets.
The possible security holes have been extensively scrutinized,
but are possibly incomplete.