NAME

tftpd — DARPA Internet Trivial File Transfer Protocol server

SYNOPSIS

tftpd

[-cdln] [-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:

-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.