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.\"	from: @(#)tftpd.8	8.1 (Berkeley) 6/4/93
.\"
.Dd May 5, 2015
.Dt TFTPD 8
.Os
.Sh NAME
.Nm tftpd
.Nd
.Tn DARPA
Internet Trivial File Transfer Protocol server
.Sh SYNOPSIS
.Nm
.Op Fl bcdln
.Op Fl g Ar group
.Op Fl p Ar pathsep
.Op Fl s Ar directory
.Op Fl u Ar user
.Op Ar directory ...
.Sh DESCRIPTION
.Nm
is a server which supports the
.Tn DARPA
Trivial File Transfer Protocol.
The
.Tn TFTP
server operates at the port indicated in the
.Ql tftp
service description; see
.Xr services 5 .
The server is normally started by
.Xr inetd 8 .
.Pp
The use of
.Xr tftp 1
does not require an account or password on the remote system.
Due to the lack of authentication information,
.Nm
will allow only publicly readable files to be accessed.
Filenames beginning in
.Dq Pa ../
or containing
.Dq Pa /../
are not allowed.
Unless
.Fl c
is used,
files may be written to only if they already exist and are publicly writable.
.Pp
Note that this extends the concept of
.Qq public
to include
all users on all hosts that can be reached through the network;
this may not be appropriate on all systems, and its implications
should be considered before enabling tftp service.
The server should have the user ID with the lowest possible privilege.
.Pp
Access to files may be restricted by invoking
.Nm
with a list of directories by including up to 20 pathnames
as server program arguments in
.Pa /etc/inetd.conf .
In this case access is restricted to files whose
names are prefixed by the one of the given directories.
The given directories are also treated as a search path for
relative filename requests.
.Pp
The options are:
.Bl -tag -width "XsXdirectoryX"
.It Fl b
Allow clients which return acknowledgements to the broadcast address to
communicate with the tftp server.
Some tftp clients, notably ones resident in the ROMs of older Cisco
equipment, return their acknowledgements to the broadcast address rather
than the server's unicast address.  
.It Fl c
Allow unrestricted creation of new files.
Without this flag, only existing publicly writable files can be overwritten.
.It Fl d
Enable verbose debugging messages to
.Xr syslogd 8 .
.It Fl g Ar group
Change gid to that of
.Ar group
on startup.
If this isn't specified, the gid is set to that of the
.Ar user
specified with
.Fl u .
.It Fl l
Logs all requests using
.Xr syslog 3 .
.It Fl n
Suppresses negative acknowledgement of requests for nonexistent
relative filenames.
.It Fl p Ar pathsep
All occurrences of the single character
.Ar pathsep
(path separator) in the requested filename are replaced with
.Sq / .
.It Fl s Ar directory
.Nm
will
.Xr chroot 2
to
.Ar directory
on startup.
This is recommended for security reasons (so that files other than
those in the
.Pa /tftpboot
directory aren't accessible).
If the remote host passes the directory name as part of the
file name to transfer, you may have to create a symbolic link
from
.Sq tftpboot
to
.Sq \&.
under
.Pa /tftpboot .
.It Fl u Ar user
Change uid to that of
.Ar user
on startup.
If
.Fl u
isn't given,
.Ar user
defaults to
.Dq nobody .
If
.Fl g
isn't also given, change the gid to that of
.Ar user
as well.
.El
.Sh SEE ALSO
.Xr tftp 1 ,
.Xr inetd 8
.Rs
.%R RFC
.%N 1350
.%D July 1992
.%T "The TFTP Protocol (Revision 2)"
.Re
.Rs
.%R RFC
.%N 2347
.%D May 1998
.%T "TFTP Option Extension"
.Re
.Rs
.%R RFC
.%N 2348
.%D May 1998
.%T "TFTP Blocksize Option"
.Re
.Rs
.%R RFC
.%N 2349
.%D May 1998
.%T "TFTP Timeout Interval and Transfer Size Options"
.Re
.Sh HISTORY
The
.Nm
command appeared in
.Bx 4.2 .
.Pp
The
.Fl s
flag appeared in
.Nx 1.0 .
.Pp
The
.Fl g
and
.Fl u
flags appeared in
.Nx 1.4 .
.Pp
IPv6 support was implemented by WIDE/KAME project in 1999.
.Pp
TFTP options were implemented by Wasabi Systems, Inc., in 2003,
and first appeared in
.Nx 2.0 .
.Sh BUGS
Files larger than 33,553,919 octets (65535 blocks, last one less than 512
octets) cannot be correctly transferred without client and server
supporting blocksize negotiation (RFCs 2347 and 2348).
As a kludge,
.Nm
accepts a sequence of block numbers which wrap to zero after 65535.
.Pp
Many tftp clients will not transfer files over 16,776,703 octets
(32767 blocks), as they incorrectly count the block number using
a signed rather than unsigned 16-bit integer.
.Sh SECURITY CONSIDERATIONS
You are
.Em strongly
advised to set up
.Nm
using the
.Fl s
flag in conjunction with the name of the directory that
contains the files that
.Nm
will serve to remote hosts (e.g.,
.Pa /tftpboot ) .
This ensures that only the files that should be served
to remote hosts can be accessed by them.
.Pp
Because there is no user-login or validation within
the
.Tn TFTP
protocol, the remote site will probably have some
sort of file-access restrictions in place.
The exact methods are specific to each site and therefore
difficult to document here.
.Pp
If unrestricted file upload is enabled via the
.Fl c
option, care should be taken that this can be used
to fill up disk space in an uncontrolled manner
if this is used in an insecure environment.