libexec/ftpd/ftpd.8

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.\"     @(#)ftpd.8	8.2 (Berkeley) 4/19/94
.\" $FreeBSD$
.\"
.Dd January 27, 2000
.Dt FTPD 8
.Os BSD 4.2
.Sh NAME
.Nm ftpd
.Nd
Internet File Transfer Protocol server
.Sh SYNOPSIS
.Nm
.Op Fl 4
.Op Fl 6
.Op Fl d
.Op Fl l Op Fl l
.Op Fl A
.Op Fl D
.Op Fl R
.Op Fl S
.Op Fl U
.Op Fl r
.Op Fl E
.Op Fl T Ar maxtimeout
.Op Fl t Ar timeout
.Op Fl a Ar address
.Op Fl p Ar file
.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 indent
.It Fl d
Debugging information is written to the syslog using LOG_FTP.
.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.  Note: LOG_FTP messages
are not displayed by
.Xr syslogd 8
by default, and may have to be enabled in
.Xr syslogd 8 Ns 's
configuration file.
.It Fl D
With this option set,
.Nm
will detach and become a daemon, accepting connections on the FTP port and
forking children processes to handle them.
This is lower overhead than starting
.Nm
from
.Xr inetd 8
and is thus useful on busy servers to reduce load.
.It Fl R
With this option set,
.Nm
will revert to historical behavior with regard to security checks on
user operations and restrictions on PORT requests.
Currently,
.Nm
will only honor PORT commands directed to unprivileged ports on the
remote user's host (which violates the FTP protocol specification but
closes some security holes).
.It Fl S
With this option set,
.Nm
logs all anonymous file downloads to the file
.Pa /var/log/ftpd
when this file exists.
.It Fl U
In previous versions of
.Nm ,
when a passive mode client requested a data connection to the server,
the server would use data ports in the range 1024..4999.  Now, by default,
the server will use data ports in the range 49152..65535.  Specifying this
option will revert to the old behavior.
.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 a
When
.Fl D
is specified, accept connections only on the specified
.Ar address .
.It Fl p
When
.Fl D
is specified, write the daemon's process ID to
.Ar file .
.It Fl 6
When
.Fl D
is specified, accept connections via AF_INET6 socket.
.It Fl 4
When
.Fl D
is specified, accept IPv4 connections.
When
.Fl 6
is also specified, accept IPv4 connection via AF_INET6 socket.
When
.Fl 6
is not specified, accept IPv4 connection via AF_INET socket.
.It Fl A
Allow only anonymous ftp access.
.It Fl r
Put server in read-only mode.
All commands which may modify the local filesystem are disabled.
.It Fl E
Disable the EPSV command.
This is useful for servers behind older firewalls.
.El
.Pp
The file
.Pa /var/run/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/ftpmotd
exists,
.Nm
prints it after a successful login.  Note the motd file used is the one
relative to the login environment.  This means the one in
.Pa ~ftp/etc
in the anonymous user's case.
.Pp
The ftp server currently supports the following ftp requests.
The case of the requests is ignored.  Requests marked [RW] are
disabled if
.Fl r
is specified.
.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 [RW]"
.It CDUP Ta "change to parent of current working directory"
.It CWD Ta "change working directory"
.It DELE Ta "delete a file [RW]"
.It EPRT Ta "specify data connection port, multiprotocol"
.It EPSV Ta "prepare for server-to-server transfer, multiprotocol"
.It HELP Ta "give help information"
.It LIST Ta "give list files in a directory" Pq Dq Li "ls -lgA"
.It LPRT Ta "specify data connection port, multiprotocol"
.It LPSV Ta "prepare for server-to-server transfer, multiprotocol"
.It MDTM Ta "show last modification time of file"
.It MKD Ta "make a directory [RW]"
.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 [RW]"
.It RNFR Ta "specify rename-from file name [RW]"
.It RNTO Ta "specify rename-to file name [RW]"
.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 [RW]"
.It STOU Ta "store a file with a unique name [RW]"
.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) [RW]"
.It XPWD Ta "print the current working directory (deprecated)"
.It XRMD Ta "remove a directory (deprecated) [RW]"
.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 [RW], 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 six rules.
.Pp
.Bl -enum -offset indent
.It
The login name must be in the password data base
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 key 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 login name must not be a member of a group specified in the file
.Pa /etc/ftpusers .
Entries in this file interpreted as group names are prefixed by an "at"
.Ql \&@
sign.
.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 ,
or the user is a member of a group with a group entry in this file,
i.e. one prefixed with
.Ql \&@ ,
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).
This facility may also be triggered by enabling the boolean "ftp-chroot"
capability in
.Xr login.conf 5 .
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).
When the
.Fl S
option is set, all transfers are logged as well.
.El
.Pp
In the last case,
.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.
.It Pa ~ftp/etc
Make this directory owned by
.Dq root
and unwritable by anyone (mode 555).
The files pwd.db (see
.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 passwd
is not used, and should not contain real passwords.
The file
.Pa ftpmotd ,
if present, will be printed after a successful login.
These files should be mode 444.
.It Pa ~ftp/pub
Make this directory mode 777 and owned by
.Dq ftp .
Guests
can then place files which are to be accessible via the anonymous
account in this directory.
.El
.Pp
If the system has multiple IP addresses,
.Nm
supports the idea of virtual hosts, which provides the ability to
define multiple anonymous ftp areas, each one allocated to a different
internet address.
The file
.Pa /etc/ftphosts
contains information pertaining to each of the virtual hosts.
Each host is defined on its own line which contains a number of
fields separated by whitespace:
.Bl -tag -offset indent -width hostname
.It hostname
Contains the hostname or IP address of the virtual host.
.It user
Contains a user record in the system password file.
As with normal anonymous ftp, this user's access uid, gid and group
memberships determine file access to the anonymous ftp area.
The anonymous ftp area (to which any user is chrooted on login)
is determined by the home directory defined for the account.
User id and group for any ftp account may be the same as for the
standard ftp user.
.It statfile
File to which all file transfers are logged, which
defaults to
.Pa /var/log/ftpd .
.It welcome
This file is the welcome message displayed before the server ready
prompt.
It defaults to
.Pa /etc/ftpwelcome .
.It motd
This file is displayed after the user logs in.
It defaults to
.Pa /etc/ftpmotd .
.El
.Pp
Lines beginning with a '#' are ignored and can be used to include
comments.
.Pp
Defining a virtual host for the primary IP address or hostname
changes the default for ftp logins to that address.
The 'user', 'statfile', 'welcome' and 'motd' fields may be left
blank, or a single hypen '-' used to indicate that the default
value is to be used.
.Pp
As with any anonymous login configuration, due care must be given
to setup and maintenance to guard against security related problems.
.Pp
.Nm
has internal support for handling remote requests to list
files, and will not execute
.Pa /bin/ls
in either a chrooted or non-chrooted environment.  The
.Pa ~/bin/ls
executable need not be placed into the chrooted tree, nor need the
.Pa ~/bin
directory exist.
.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/ftphosts
Virtual hosting configuration file.
.It Pa /etc/ftpwelcome
Welcome notice.
.It Pa /etc/ftpmotd
Welcome notice after login.
.It Pa /var/run/nologin
Displayed and access refused.
.It Pa /var/log/ftpd
Log file for anonymous transfers.
.El
.Sh SEE ALSO
.Xr ftp 1 ,
.Xr key 1 ,
.Xr getusershell 3 ,
.Xr login.conf 5 ,
.Xr inetd 8 ,
.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 .
IPv6 support was added in WIDE Hydrangea IPv6 stack kit.