atftpd.8

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.TH ATFTPD 8 "December 27, 2000"
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.SH NAME
atftpd \- Trivial File Transfer Protocol Server.
.SH SYNOPSIS
.B atftpd
.RI [ options ] " directory"

.SH DESCRIPTION
.B atftpd
is a TFTP (RFC1350) server. By default it is started by inetd on most
systems, but may run as a stand alone daemon. This server is
multi-threaded and supports all options described in RFC2347 (option
extension), RFC2348 (blksize), RFC2349 (tsize and timeout) and RFC2090
(multicast option). It also supports mtftp as defined in the PXE
specification.

.SH OPTIONS
This program supports both the usual GNU command line syntax, with
long options starting with two dashes ('-') as well as short
options. A description of the options is included below.

.TP
.B \-t, \-\-tftpd\-timeout <value>
Number of seconds of inactivity before the server exits. This value
has meaning only when the server is started by inetd. In daemon mode,
the server never exits. Default is 300 seconds.

.TP
.B \-r, \-\-retry\-timeout <value>
How many seconds to wait for a reply before retransmitting a
packet. Default is 5 seconds. This can be overridden by the TFTP
client with the 'timeout' option.

.TP
.B \-m, \-\-maxthread <value>
Maximum number of concurrent threads allowed. Default is 100.

.TP
.B \-v, \-\-verbose[=value]
Increase or set the logging level. No arguments will increase by one
the current value. Default is LOG_NOTICE, see syslog(3) for log
level. Valid value range from 0 (LOG_EMERG) to 7 (LOG_DEBUG).

.TP
.B \-\-trace
When verbose level is set to 7, this will output debug information for
each packet sent or received from the network.

.TP
.B \-\-no\-timeout
disable 'timeout' from RFC2349. This will prevent the server from
acknowledging the 'timeout' option requested by the client.

.TP
.B \-\-no\-tsize
disable 'tsize' from RFC2349. This will prevent the server from
acknowledging the 'tsize' option requested by the client.

.TP
.B \-\-no\-blksize
disable 'blksize' from RFC2348. This will prevent the server from
acknowledging the 'blksize' request by the client.

.TP
.B \-\-no\-windowsize
disable 'windowsize' from RFC7440. This will prevent the server from
acknowledging the 'windowsize' request by the client.

.TP
.B \-\-no\-multicast
disable 'multicast' from RFC2090. This will prevent the server from
acknowledging the 'multicast' request by the client.

.TP
.B \-\-logfile <logfile>
Log to a specific file instead of only syslog. 'nobody' (or any user
used to run the server) must have permissions on the given
file. Assuming the file is /var/log/atftpd.log, simply run: "touch
/var/log/atftpd.log" and then "chown nobody.nogroup
/var/log/atftpd.log". When the server is run in daemon mode,
/dev/stdout or /dev/stderr can be used.  Specifying a single dash as
the filename will send logs to stdout (file descriptor 1).

.TP
.B \-\-pidfile
Write the PID of the server to the specified file. This may be useful
when automatically starting and stopping one or more instance of the
server.

.TP
.B \-\-daemon
Run as a daemon. Do not use this option if atftpd is started by inetd.

.TP
.B \-\-no-fork
When \-\-daemon is specified, this option will prevent the server from
forking to background. It is useful for debugging purpose or
specialized usage.

.TP
.B \-\-user <user[.group]>
By default, the server change identity to the user nobody and group
nogroup. Specify an alternate user.group with this option.

.TP
.B \-\-group <group>
Alternate way of specifying the group. If group is specified with
\-\-user and \-\-group, the last option will be used.

.TP
.B \-\-port <number>
Specify the port on which atftpd listens. Useful when \-\-daemon is
specified. Default is standard tftp port as determined 
by \fIgetservbyname\fR\|(3).

.TP
.B \-\-bind\-address <IP address>
Specify the IP address which atftpd binds to. Useful when \-\-daemon is
specified. Default is to bind to all interfaces. Only one address can
be specified, the server can only listen to one or all interfaces.

.TP
.B \-\-mcast\-ttl
Specify the TTL to be used for multicast datagram. By default a value
of 1 is used. Note that TTL has a special meaning in multicast as it
is used to determine the scope of the packets. The value of 1 means
the packets don't leave the local network, see ip(4). Scope may also
be determine by the address as described RFC2365.

.TP
.B \-\-mcast\-addr
Specify the IP address range to be used for multicast transfer. Format
string may comprise range and list of values:
"239.255.0.0-31,128-132,200".
Default value is "239.255.0.0-255". This address range is proposed in
RFC2365 for local scope.

.TP
.B \-\-mcast\-port
Specify the UDP port to use for multicast transfer. Format string may
contain range and list of port number: "1758-2000,8000-9000". default
value is "1758".

.TP
.B \-\-pcre <file>
Specify a pattern/replacement file to use. This allows one to replace
requested file name based on Perl Compatible Regular Expression. See
README.PCRE.

.TP
.B \-\-pcre\-test <file>
Test a pattern/replacement file. When using this option, the server
will not start as usual but just read file name from stdin and
printout the substitution.

.TP
.B \-\-mtftp <file>
This will start a mtftp server thread for each valid entry in the
supplied file. See PXE specification for detail about mtftp. An
example file is provided in the source distribution.

.TP
.B \-\-mtftp\-port <port>
Port the mtftp server shall listen to for incoming request.

.TP
.B \-\-no\-source\-port\-checking
In some specific cases of networks using load balancer or other
equipment performing NAT (network address translation), some needs to
disable source port checking because port number as been translated. If
you want to use this feature, you must know why you need it and the
implication. Be aware that this option violate the RFC1350. This
option has effect only for non-multicast transfer.

.TP
.B \-\-prevent\-sas
Address the Sorcerer's Apprentice Syndrome situation as requested by RFC 1350.
This RFC requires repeated responses to a single packet to be
rejected. Thus a block will only get retransmitted on a timeout.
For backward compatibility, the default stays to ignore this RFC.
So blocks get transmitted on every request.

.TP
.B \-\-mcast\-switch\-client
This option allows the server to proceed with the next multicast client
as soon as the current client timeout. When the current master client
fails to send an acknowledge (ACK) to the server, the server will send
an option acknowledge (OACK) to the master client with the field MC
(master client) set to false and send an OACK to the next multicast
client with MC set to true. Without this option, the server will retry
the current master client up to 5 times and then mark it done,
proceeding with the next one.

.TP
.B \-V, \-\-version
Show version of program.

.TP
.B \-h, \-\-help
Show summary of options.

.TP
.B path
This is the root directory used by the TFTP server. All requested
files from a TFTP client must reside in this directory. If not
specified, the directory defaults to /tftpboot. Since
atftpd run as the nobody user, the permission of the directory
must be set properly to allow file reading and writing.

.SH STATS
Starting with release 0.2, the server collects some statistics.
Currently the server compute system load, time between connections and
some thread statistics like number of file sent, received, number of
abort... To see those stats in the logs, you need to set --verbose=6
(LOG_NOTICE) or higher.

.SH SECURITY
TFTP by itself has no provision for security. There is no user
authentication and TFTP clients get access to all files within the
specified root directory for which the server has permission.

Some level of security can be gained using atftp libwrap
support. Adding proper entry to /etc/hosts.allow and /etc/hosts.deny
will restrict access to trusted hosts. Daemon name to use in these
files is in.tftpd.

.SH PCRE
The atftpd server provides a way to dynamically replace requested file
name by a new one based on Perl compatible regular expression. Pairs
of pattern/replacement are read from the specified files. Upon
reception of a read request, the server will first try to open the
file name requested. If it fails, then it will search for a
replacement based on the content of the pattern file. If this still
fails, then an error will be sent to the client. This feature is
available only for read request. It makes no sense doing this
substitution for client writing files to the server.

.SH MTFTP
The mtftp name refer to multicasrt tftp as define by the PXE
specification. See pxespec.txt for the source of the
specification. Note that this is not the same as RFC2090. PXE
compliant boot implements mtftp, not RFC2090.

.SH FIFO
The atftpd server provides the ability to communicate with other
processes using named pipes / FIFOs. In addition to files you can
place FIFOs into the specified root directory which atftpd will open 
for reading on a client request and serve the content to the client.
This feature can be used on the tftp server side to tell the clients 
(separately, if you want) to boot from network or to boot from their 
fallback boot method.

\fBExample\fR

 #!/usr/bin/perl
 use POSIX;
 my $pipe = "/tftpboot/linux/pxelinux.cfg/01-00-01-02-03-04-05";
 # create fifo
 POSIX::mkfifo($pipe, 0644) or
    die("cannot create Pipe $pipe: $!\\n");
 # open pipe
 sysopen(FIFO, $pipe, O_WRONLY, 0644);
 # write boot configuration
 print FIFO "default linux\\r\\n";
 print FIFO "label linux\\r\\n";
 print FIFO " kernel vmlinuz\\r\\n";
 print FIFO " append ramdisk_size=64000 init=/etc/init initrd=initrd\\r\\n";
 close(FIFO);
 # delete pipe
 unlink($pipe);


.SH SEE ALSO
.BR inetd (8), hosts_access (5), libpcre (7),
RFC1350, RFC2090, RFC2347, RFC2348, RFC2349 and pxespec.pdf.
.SH AUTHOR
This manual page was written by Remi Lefebvre <remi@debian.org> and Jean-Pierre
Lefebvre <helix@step.polymtl.ca>.