Ubuntu Manpage: tftpd - Trivial File Transfer Protocol server

Provided by: tftpd-hpa_5.2+20240610-3_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.

Specify the number of remapping rules that may be executed before the
filename mapping fails. The default is 4096.

--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.

gg Repeat this rule until it no longer matches, but only on the portion of the string that has not
yet been matched, similar to how the s command with the g option works in sed(1). 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.

E If this rule matches, and the result matches a filename that can be transferred, end rule
processing after executing the rule. If this is combined with r, then if the substitution does not
result in a valid filename, the substitution is undone. This cannot be combined with g, but can be
combined with gg.

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 a 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
whose 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.