NetBSD/libexec/ftpd/ftpd.8

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.\"     @(#)ftpd.8	8.2 (Berkeley) 4/19/94
.\"
.Dd April 19, 1994
.Dt FTPD 8
.Os BSD 4.2
.Sh NAME
.Nm ftpd
.Nd
Internet File Transfer Protocol server
.Sh SYNOPSIS
.Nm
.Op Fl dl
.Op Fl a Ar anondir
.Op Fl T Ar maxtimeout
.Op Fl t Ar timeout
.Op Fl u Ar umask
.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
Available options:
.Bl -tag -width Ds
.It Fl a
Define the directory to which we chroot for anonymous logins.
Default is the home directory for the ftp user.
.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.
.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 u      
Sets the default umask.  Must be in octal form, e.g. "002"
.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 file
.Pa /etc/motd
exists,
.Nm
prints it after a successful login.
.Pp
The
.Pa /etc/ftpusers
file is used to determine which users may use ftp.
If the file does not exist, all users are denied access.  If it
does exist, each line is a a comment starting with ``#'' or a
glob pattern that uses the same syntax as /bin/sh, optionally
followed by whitespace and ``allow'' or ``deny''.
Each glob pattern is compared in turn against the username
until a match is found.  If the word following the matched glob
pattern is ``allow'' the user is granted access; if the word is
anything else, or nothing at all, the user is denied access.
(No further comparisons are attempted after the first successful match.)
If no match is found, the user is granted access.
This syntax is backward-compatable with the old syntax.
.Pp

If a user requests a guest login, the ftp server checks to see that
both ``anonymous'' and ``ftp'' have access, so if you deny all
users by default, you will need to add both ``anonymous allow''
and ``ftp allow'' to
.Pa /etc/ftpusers
in order to allow guest logins.
.Pp
The ftp server currently supports the following ftp requests.
The case of the requests is ignored.
.Bl -column "Request" -offset indent
.It Request Ta "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 HELP Ta "give help information"
.It LIST Ta "give list files in a directory" Pq Dq Li "ls -lgA"
.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"
.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 according to five rules. 
.Pp
.Bl -enum -offset indent
.It
The login name must be in the password data base,
.Pa /etc/pwd.db ,
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 skey 1
for more information on S/Key authentication. S/Key is a Trademark of
Bellcore.
.It
The login name must be allowed based on the information in
.Pa /etc/ftpusers
(see above).
.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
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
In the last case, 
.Nm
takes special measures to restrict the client's access privileges.
The server disables the MKD, XMKD, RMD, XRMD, DELE, SITE UMASK, and
SITE CHMOD commands, sets the umask to 0707, and 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/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).
The program
.Xr ls 1
must be present to support the list command.
This program should be 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 
.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 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 ``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
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
Anonymous users will be able to upload files 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.
.El
.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/ftpwelcome
Welcome notice.
.It Pa /etc/motd
Welcome notice after login.
.It Pa /etc/nologin
Displayed and access refused.
.El
.Sh SEE ALSO
.Xr ftp 1 ,
.Xr skey 1 ,
.Xr getusershell 3 ,
.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 .