libexec/ftpd/ftpd.8

.\"	$OpenBSD: ftpd.8,v 1.76 2019/05/08 23:56:48 tedu Exp $
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.\"     @(#)ftpd.8	8.2 (Berkeley) 4/19/94
.\"
.Dd $Mdocdate: May 8 2019 $
.Dt FTPD 8
.Os
.Sh NAME
.Nm ftpd
.Nd Internet File Transfer Protocol server
.Sh SYNOPSIS
.Nm ftpd
.Op Fl 46ADdlMnPSUW
.Op Fl m Ar minuid
.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 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 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 A
Permit only anonymous FTP connections
(unless the
.Fl n
option is specified),
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
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 d
Debugging information is written to the syslog using
.Dv LOG_FTP .
.It Fl l
Each successful and failed
FTP session is logged using syslog with a facility of
.Dv 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 m Ar minuid
Disallow login to user accounts with a UID below
.Ar minuid .
The default is 1000, to prevent access to administrative and daemon accounts.
Anonymous access is allowed even if the UID of the FTP user is smaller than
.Ar minuid .
.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
.Nm
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 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
Each concurrent
FTP session is logged to the file
.Pa /var/run/utmp ,
making them visible to commands such as
.Xr who 1 .
.Fl U
and
.Fl W
are mutually exclusive.
.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.
.It Fl W
Do not save login records to
.Pa /var/log/wtmp .
.Fl W
and
.Fl U
are mutually exclusive.
.El
.Pp
The file
.Pa /etc/nologin
can be used to disable FTP access.
If the file exists,
.Nm
displays it and exits.
Note: this method will disable
.Em all
non-root logins; see
.Xr login 1
for further details.
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 (not implemented)"
.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"
.It EPSV Ta "prepare for server-to-server transfer"
.It HELP Ta "give help information"
.It LIST Ta "give list of files in a directory" Pq Li "ls -lgA"
.It LPRT Ta "specify data connection port"
.It LPSV Ta "prepare for server-to-server transfer"
.It MDTM Ta "show last modification time of file"
.It MKD Ta "make a directory"
.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 REIN Ta "reinitialize (not implemented)"
.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 SMNT Ta "structure mount (not implemented)"
.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 (deprec.)"
.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 UNIX specific commands
are supported by the SITE request:
.Bl -column Request -offset indent
.It Sy Request Ta Sy Description
.It CHMOD Ta "change mode of a file, e.g., SITE CHMOD 755 filename"
.It HELP Ta "give help information"
.It IDLE Ta "set idle-timer, e.g., SITE IDLE 60"
.It UMASK Ta "change umask, e.g., SITE UMASK 002"
.El
.Pp
The remaining FTP requests specified in Internet RFC 959 are recognized,
but not implemented.
MDTM and SIZE are specified in RFC 3659.
.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
.Pq Sq :\&
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 the following rules.
.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 account must have a UID not less than
.Ar minuid .
.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 ,
which is a text file containing one user name per line,
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):
.Bd -literal -offset indent
/usr/libexec/auth/approve_ftpd -v FTPD_HOST=ftp.mycompany.com \e
	username class 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/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 to the FTP chroot space) of the file transferred.
.It type
The type of transfer; either
.Sq a
for ASCII or
.Sq b
for binary.
.It unused
Unused field containing a
.Sq * ,
for compatibility.
.It unused
Unused field containing an
.Sq o ,
for compatibility.
.It user type
The type of user; either
.Sq a
for anonymous or
.Sq 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 service name
The network service name (always ftp).
.It unused
Unused field containing a
.Sq 0 ,
for compatibility.
.It real name
The system login name if the connection is not anonymous, or a
.Sq *
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
.Va net.inet.ip.porthifirst
and
.Va net.inet.ip.porthilast .
.Sh FILES
.Bl -tag -width /etc/ftpwelcome -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/log/wtmp
login account records
.It Pa /var/run/utmp
list of users on the system
.El
.Sh SEE ALSO
.Xr ftp 1 ,
.Xr login 1 ,
.Xr skey 1 ,
.Xr who 1 ,
.Xr chroot 2 ,
.Xr ctime 3 ,
.Xr group 5 ,
.Xr login.conf 5 ,
.Xr motd 5 ,
.Xr services 5 ,
.Xr shells 5 ,
.Xr ftp-proxy 8 ,
.Xr inetd 8 ,
.Xr pwd_mkdb 8 ,
.Xr sysctl 8 ,
.Xr syslogd 8
.Sh STANDARDS
.Rs
.%A J. Postel
.%A J. Reynolds
.%D October 1985
.%R RFC 959
.%T FILE TRANSFER PROTOCOL (FTP)
.Re
.Pp
.Rs
.%A P. Hethmon
.%D March 2007
.%R RFC 3659
.%T Extensions to FTP
.Re
.Sh HISTORY
The
.Nm
command appeared in
.Bx 4.2 .