TFTPD(8) System Manager's Manual TFTPD(8)
NAME
tftpd – Internet Trivial File Transfer Protocol server
SYNOPSIS
tftpd [-cdCilnow] [-F strftime-format] [-s directory] [-u user]
[-U umask] [directory ...]
DESCRIPTION
The tftpd utility is a server which supports the Internet Trivial File
Transfer Protocol (RFC 1350). The TFTP server operates at the port
indicated in the ‘tftp’ service description; see services(5). This
server should not be started manually; instead, it should be run using
launchd(8) using the plist /System/Library/LaunchDaemons/tftp.plist. It
may be started using the launchctl(1) load command; refer to the
documentation for that utility for more information.
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. Files containing the string
“/../” or starting with “../” are not allowed. Files may be written 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 /System/Library/LaunchDaemons/tftp.plist. 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 -s option provides additional security by changing the root directory
of tftpd, thereby prohibiting accesses to outside of the specified
directory. Because chroot(2) requires super-user privileges, tftpd must
be run as root. However, after performing the chroot(2) call, tftpd will
set its user ID to that of the specified user, or “nobody” if no -u
option is specified.
The options are:
-c Changes the default root directory of a connecting host via
chroot(2) based on the connecting IP address. This prevents
multiple clients from writing to the same file at the same time.
If the directory does not exist, the client connection is
refused. The -s option is required for -c and the specified
directory is used as a base.
-C Operates the same as -c except it falls back to directory
specified via -s if a directory does not exist for the client's
IP.
-F Use this strftime(3) compatible format string for the creation of
the suffix if -W is specified. By default the string "%Y%m%d" is
used.
-d, -d [value]
Enables debug output. If value is not specified, then the debug
level is increased by one for each instance of -d which is
specified.
If value is specified, then the debug level is set to value. The
debug level is a bitmask implemented in
src/libexec/tftpd/tftp-utils.h. Valid values are 0 (DEBUG_NONE),
1 (DEBUG_PACKETS), 2, (DEBUG_SIMPLE), 4 (DEBUG_OPTIONS), and 8
(DEBUG_ACCESS). Multiple debug values can be combined in the
bitmask by logically OR'ing the values. For example, specifying
-d 15 will enable all the debug values.
-i Ignored for backward compatibility.
-l Log all requests using syslog(3) with the facility of LOG_FTP.
Note: Logging of LOG_FTP messages must also be enabled in the
syslog configuration file, syslog.conf(5).
-n Suppress negative acknowledgement of requests for nonexistent
relative filenames.
-o Disable support for RFC2347 style TFTP Options.
-s directory
Cause tftpd to change its root directory to directory. After
doing that but before accepting commands, tftpd will switch
credentials to an unprivileged user.
-u user
Switch credentials to user (default “nobody”) when the -s option
is used. The user must be specified by name, not a numeric UID.
-U umask
Set the umask for newly created files. The default is 022
(S_IWGRP | S_IWOTH).
-w Allow write requests to create new files. By default tftpd
requires that the file specified in a write request exist. Note
that this only works in directories writable by the user
specified with -u option
-W As -w but append a YYYYMMDD.nn sequence number to the end of the
filename. Note that the string YYYYMMDD can be changed with the
-F option.
SEE ALSO
launchctl(1), tftp(1), chroot(2), syslog(3), launchd.plist(5),
services(5), syslog.conf(5), launchd(8)
The following RFC's are supported:
RFC 1350: The TFTP Protocol (Revision 2).
RFC 2347: TFTP Option Extension.
RFC 2348: TFTP Blocksize Option.
RFC 2349: TFTP Timeout Interval and Transfer Size Options.
RFC 7440: TFTP Windowsize Option.
The non-standard rollover and blksize2 TFTP options are mentioned here:
Extending TFTP, http://www.compuphase.com/tftp.htm.
HISTORY
The tftpd utility appeared in 4.2BSD; the -s option was introduced in
FreeBSD 2.2, the -u option was introduced in FreeBSD 4.2, the -c option
was introduced in FreeBSD 4.3, and the -F and -W options were introduced
in FreeBSD 7.4.
Support for Timeout Interval and Transfer Size Options (RFC2349) was
introduced in FreeBSD 5.0, support for the TFTP Blocksize Option
(RFC2348) and the blksize2 option was introduced in FreeBSD 7.4.
Edwin Groothuis <edwin@FreeBSD.org> performed a major rewrite of the
tftpd and tftp(1) code to support RFC2348.
Support for the windowsize option (RFC7440) was introduced in
FreeBSD 13.0.
NOTES
Files larger than 33,553,919 octets (65535 blocks, last one <512 octets)
cannot be correctly transferred without client and server supporting
blocksize negotiation (RFCs 2347 and 2348), or the non-standard TFTP
rollover option. As a kludge, tftpd accepts a sequence of block number
which wrap to zero after 65535, even if the rollover option is not
specified.
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.
macOS 15.2 March 2, 2020 macOS 15.2