NetBSD/libexec/ftpd/ftpd.8

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.\"     @(#)ftpd.8	6.9 (Berkeley) 3/16/91
.\"
.Dd March 16, 1991
.Dt FTPD 8
.Os BSD 4.2
.Sh NAME
.Nm ftpd
.Nd
.Tn DARPA
Internet File Transfer Protocol server
.Sh SYNOPSIS
.Nm ftpd
.Op Fl d
.Op Fl l
.Op Fl t Ar timeout
.Op Fl T Ar maxtimeout
.Sh DESCRIPTION
.Nm Ftpd
is the
.Tn DARPA
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 d
Debugging information is written to the syslog.
.It Fl l
Each
.Xr ftp 1
session is logged in the syslog.
.It Fl t
The inactivity timeout period is set to
.Ar timeout
seconds (the default is 15 minutes).
.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.
.El
.Pp
The ftp server currently supports the following ftp
requests; case is not distinguished.
.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. Em E.g. SITE UMASK 002
.It IDLE Ta set idle-timer. Em E.g. SITE IDLE 60
.It CHMOD Ta change mode of a file. Em E.g.
SITE CHMOD 755 filename
.It HELP Ta give help information. Em E.g. SITE HELP
.El
.Pp
The remaining ftp requests specified in Internet
.%T "RFC 959"
are
recognized, but not implemented.
MDTM and SIZE are not specified in
.%T "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
.%T "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 three rules. 
.Pp
.Bl -enum -offset indent
.It
The user name must be in the password data base,
.Pa /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.
.It
The user name must not appear in the file
.Pa /etc/ftpusers .
.It
The user must have a standard shell returned by 
.Xr getusershell 3 .
.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 this
is given as the client host's name).
.El
.Pp
In the last case, 
.Nm ftpd
takes special measures to restrict the client's access privileges.
The server performs a 
.Xr chroot 2
command 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;  the following
rules are recommended.
.Bl -tag -width "~ftp/pub" -offset indent
.It Pa ~ftp
Make the home directory owned by
.Dq ftp
and unwritable by anyone.
.It Pa ~ftp/bin
Make this directory owned by the super-user and unwritable by
anyone.  The program
.Xr ls 1
must be present to support the list command.  This
program should have mode 111.
.It Pa ~ftp/etc
Make this directory owned by the super-user and unwritable by
anyone.  The files
.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 encrypted passwords.
These files should be mode 444.
.It Pa ~ftp/pub
Make this directory mode 777 and owned by
.Dq ftp .
Users
should then place files which are to be accessible via the
anonymous account in this directory.
.El
.Sh SEE ALSO
.Xr ftp 1 ,
.Xr getusershell 3 ,
.Xr syslogd 8
.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.
.Sh HISTORY
The
.Nm
command appeared in
.Bx 4.2 .