NAME
tftpd —
DARPA Internet Trivial File
Transfer Protocol server
SYNOPSIS
tftpd |
[-bcdln]
[-g group]
[-p
pathsep]
[-s
directory]
[-u user]
[directory ...] |
DESCRIPTION
tftpd is a server which supports the DARPA Trivial File
Transfer Protocol. The TFTP server operates at the port indicated in the
‘
tftp
’ service description; see
services(5). The server is
normally started by
inetd(8).
The use of
tftp(1) does not require
an account or password on the remote system. Due to the lack of authentication
information,
tftpd will allow only publicly readable files
to be accessed. Filenames beginning in “
../” or
containing “
/../” are not allowed. Unless
-c is used, files may be written to only if they already
exist and are publicly writable.
Note that this extends the concept of “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.
Access to files may be restricted by invoking
tftpd with a
list of directories by including up to 20 pathnames as server program
arguments in
/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.
The options are:
-
-
- -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.
-
-
- -c
- Allow unrestricted creation of new files. Without this
flag, only existing publicly writable files can be overwritten.
-
-
- -d
- Enable verbose debugging messages to
syslogd(8).
-
-
- -g
group
- Change gid to that of group on
startup. If this isn't specified, the gid is set to that of the
user specified with -u.
-
-
- -l
- Logs all requests using
syslog(3).
-
-
- -n
- Suppresses negative acknowledgement of requests for
nonexistent relative filenames.
-
-
- -p
pathsep
- All occurances of the single character
pathsep (path separator) in the requested filename
are replaced with ‘/’.
-
-
- -s
directory
- tftpd will
chroot(2) to
directory on startup. This is recommended for
security reasons (so that files other than those in the
/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 ‘tftpboot’ to
‘.’ under /tftpboot.
-
-
- -u
user
- Change uid to that of user on
startup. If -u isn't given, user
defaults to “nobody”. If -g isn't also
given, change the gid to that of user as well.
SEE ALSO
tftp(1),
inetd(8)
The TFTP Protocol (Revision 2),
RFC, 1350,
July 1992.
TFTP Option Extension,
RFC, 2347,
May 1998.
TFTP Blocksize Option,
RFC, 2348,
May 1998.
TFTP Timeout Interval and Transfer Size
Options, RFC, 2349,
May 1998.
HISTORY
The
tftpd command appeared in
4.2BSD.
The
-s flag appeared in
NetBSD 1.0.
The
-g and
-u flags appeared in
NetBSD 1.4.
IPv6 support was implemented by WIDE/KAME project in 1999.
TFTP options were implemented by Wasabi Systems, Inc., in 2003, and first
appeared in
NetBSD 2.0.
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,
tftpd accepts a sequence of block numbers which wrap to zero
after 65535.
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.
SECURITY CONSIDERATIONS
You are
strongly advised to set up
tftpd
using the
-s flag in conjunction with the name of the
directory that contains the files that
tftpd will serve to
remote hosts (e.g.,
/tftpboot). This ensures that only the
files that should be served to remote hosts can be accessed by them.
Because there is no user-login or validation within the 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.
If unrestricted file upload is enabled via the
-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.