Provided by: tftpd-hpa_5.2+20150808-1ubuntu1.16.04.1_amd64 
NAME
tftpd - Trivial File Transfer Protocol server
SYNOPSIS
in.tftpd [options...] directory...
DESCRIPTION
tftpd is a server for the Trivial File Transfer Protocol. The TFTP protocol is
extensively used to support remote booting of diskless devices. The server is normally
started by inetd, but can also run standalone.
OPTIONS
--ipv4, -4
Connect with IPv4 only, even if IPv6 support was compiled in.
--ipv6, -6
Connect with IPv6 only, if compiled in.
-l, --listen
Run the server in standalone (listen) mode, rather than run from inetd. In listen
mode, the --timeout option is ignored, and the --address option can be used to
specify a specific local address or port to listen to.
--foreground, -L
Similar to --listen but do not detach from the foreground process. Implies
--listen.
--address [address][:port], -a [address][:port]
Specify a specific address and port to listen to when called with the --listen or
--foreground option. The default is to listen to the tftp port specified in
/etc/services on all local addresses.
Please note: Numeric IPv6 adresses must be enclosed in square brackets to avoid
ambiguity with the optional port information.
--create, -c
Allow new files to be created. By default, tftpd will only allow upload of files
that already exist. Files are created with default permissions allowing anyone to
read or write them, unless the --permissive or --umask options are specified.
--secure, -s
Change root directory on startup. This means the remote host does not need to pass
along the directory as part of the transfer, and may add security. When --secure
is specified, exactly one directory should be specified on the command line. The
use of this option is recommended for security as well as compatibility with some
boot ROMs which cannot be easily made to include a directory name in its request.
--user username, -u username
Specify the username which tftpd will run as; the default is "nobody". The user
ID, group ID, and (if possible on the platform) the supplementary group IDs will be
set to the ones specified in the system permission database for this username.
--umask umask, -U umask
Sets the umask for newly created files to the specified value. The default is zero
(anyone can read or write) if the --permissive option is not specified, or
inherited from the invoking process if --permissive is specified.
--permissive, -p
Perform no additional permissions checks above the normal system-provided access
controls for the user specified via the --user option.
--pidfile pidfile, -P pidfile
When run in standalone mode, write the process ID of the listening server into
pidfile. On normal termination (SIGTERM or SIGINT) the pid file is automatically
removed.
--timeout timeout, -t timeout
When run from inetd this specifies how long, in seconds, to wait for a second
connection before terminating the server. inetd will then respawn the server when
another request comes in. The default is 900 (15 minutes.)
--retransmit timeout, -T timeout
Determine the default timeout, in microseconds, before the first packet is
retransmitted. This can be modified by the client if the timeout or utimeout
option is negotiated. The default is 1000000 (1 second.)
--map-file remap-file, -m remap-file
Specify the use of filename remapping. The remap-file is a file containing the
remapping rules. See the section on filename remapping below. This option may not
be compiled in, see the output of in.tftpd -V to verify whether or not it is
available.
--verbose, -v
Increase the logging verbosity of tftpd. This flag can be specified multiple times
for even higher verbosity.
--verbosity value
Set the verbosity value to value.
--refuse tftp-option, -r tftp-option
Indicate that a specific RFC 2347 TFTP option should never be accepted.
--blocksize max-block-size, -B max-block-size
Specifies the maximum permitted block size. The permitted range for this parameter
is from 512 to 65464. Some embedded clients request large block sizes and yet do
not handle fragmented packets correctly; for these clients, it is recommended to
set this value to the smallest MTU on your network minus 32 bytes (20 bytes for IP,
8 for UDP, and 4 for TFTP; less if you use IP options on your network.) For
example, on a standard Ethernet (MTU 1500) a value of 1468 is reasonable.
--port-range port:port, -R port:port
Force the server port number (the Transaction ID) to be in the specified range of
port numbers.
--version, -V
Print the version number and configuration to standard output, then exit
gracefully.
RFC 2347 OPTION NEGOTIATION
This version of tftpd supports RFC 2347 option negotation. Currently implemented options
are:
blksize (RFC 2348)
Set the transfer block size to anything less than or equal to the specified option.
This version of tftpd can support any block size up to the theoretical maximum of
65464 bytes.
blksize2 (nonstandard)
Set the transfer block size to anything less than or equal to the specified option,
but restrict the possible responses to powers of 2. The maximum is 32768 bytes
(the largest power of 2 less than or equal to 65464.)
tsize (RFC 2349)
Report the size of the file that is about to be transferred. This version of tftpd
only supports the tsize option for binary (octet) mode transfers.
timeout (RFC 2349)
Set the time before the server retransmits a packet, in seconds.
utimeout (nonstandard)
Set the time before the server retransmits a packet, in microseconds.
rollover (nonstandard)
Set the block number to resume at after a block number rollover. The default and
recommended value is zero.
The --refuse option can be used to disable specific options; this may be necessary to work
around bugs in specific TFTP client implementations. For example, some TFTP clients have
been found to request the blksize option, but crash with an error if they actually get the
option accepted by the server.
FILENAME REMAPPING
The --map-file option specifies a file which contains filename remapping rules. Each non-
comment line (comments begin with hash marks, #) contains an operation, specified below; a
regex, a regular expression in the style of egrep; and optionally a replacement pattern.
The operation indicated by operation is performed if the regex matches all or part of the
filename. Rules are processed from the top down, and by default, all rules are processed
even if there is a match.
The operation can be any combination of the following letters:
r Replace the substring matched by regex by the replacement pattern. The replacement
pattern may contain escape sequences; see below.
g Repeat this rule until it no longer matches. This is always used with r.
i Match the regex case-insensitively. By default it is case sensitive.
e If this rule matches, end rule processing after executing the rule.
s If this rule matches, start rule processing over from the very first rule after
executing this rule.
a If this rule matches, refuse the request and send an access denied error to the
client.
G This rule applies to GET (RRQ) requests only.
P This rule applies to PUT (WRQ) requests only.
4 This rule applies to IPv4 sessions only.
6 This rule applies to IPv6 sessions only.
~ Inverse the sense of this rule, i.e. execute the operation only if the regex
doesn't match. Cannot used together with r.
The following escape sequences are recognized as part of the replacement pattern:
\0 The entire string matched by the regex.
\1 to \9
The strings matched by each of the first nine parenthesized subexpressions, \( ...
\), of the regex pattern.
\i The IP address of the requesting host, in dotted-quad notation for IPv4 (e.g.
192.0.2.169) or conventional colon form for IPv6 (e.g. 2001:db8::1).
\x The IP address of the requesting host, in expanded hexadecimal notation (e.g.
C00002A9 for IPv4, or 20010DB8000000000000000000000001 for IPv6).
\\ Literal backslash.
\whitespace
Literal whitespace.
\# Literal hash mark.
\U Turns all subsequent letters to upper case.
\L Turns all subsequent letters to lower case.
\E Cancels the effect of \U or \L.
If the mapping file is changed, you need to send SIGHUP to any outstanding tftpd process.
SECURITY
The use of TFTP services does not require an account or password on the server system.
Due to the lack of authentication information, tftpd will allow only publicly readable
files (o+r) to be accessed, unless the --permissive option is specified. Files may be
written only if they already exist and are publicly writable, unless the --create option
is specified. 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.
Typically, some kind of firewall or packet-filter solution should be employed. If
appropriately compiled (see the output of in.tftpd --version) tftpd will query the
hosts_access(5) database for access control information. This may be slow; sites
requiring maximum performance may want to compile without this option and rely on
firewalling or kernel-based packet filters instead.
The server should be set to run as the user with the lowest possible privilege; please see
the --user flag. It is probably a good idea to set up a specific user account for tftpd,
rather than letting it run as "nobody", to guard against privilege leaks between
applications.
Access to files can, and should, be restricted by invoking tftpd with a list of
directories by including pathnames as server program arguments on the command line. In
this case access is restricted to files whole names are prefixed by one of the given
directories. If possible, it is recommended that the --secure flag is used to set up a
chroot() environment for the server to run in once a connection has been set up.
Finally, the filename remapping (--map-file flag) support can be used to provide a limited
amount of additional access control.
CONFORMING TO
RFC 1123, Requirements for Internet Hosts - Application and Support.
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.
AUTHOR
This version of tftpd is maintained by H. Peter Anvin <hpa@zytor.com>. It was derived
from, but has substantially diverged from, an OpenBSD source base, with added patches by
Markus Gutschke and Gero Kulhman.
SEE ALSO
tftp(1), egrep(1), umask(2), hosts_access(5), regex(7), inetd(8).