Trivial File Transfer Protocol (
TFTP) is a file transfer protocol
notable for its simplicity. It is generally used for automated transfer
of configuration or boot files between machines in a local environment.
Compared to FTP, TFTP is extremely limited, providing no authentication, and is rarely used interactively by a user.
Due to its simple design, TFTP could be implemented using a very small amount of memory.. It is therefore useful for booting computers such as routers which may not have any data storage dive. It is an element of the Preboot Execution Environment (PXE) network boot protocol, where it is implemented in the firmware ROM / NVRAM of the host's network card.
It is also used to transfer small amounts of data between hosts on a network, such as IP phone firmware or operating system images when a remote X Windows system terminal or any other thin client boots from a network host or server. The initial stages of some network based installation systems (such as
Solaris Jumpstart,
Red Hat Kickstart,
Symantec Ghost and
Windows NT's
Remote Installation Services) use TFTP to load a basic kernal
that performs the actual installation. It was used for saving router
configurations on Cisco routers, but was later augmented by other
protocols.
TFTP was first defined in 1980 by IEN 133
. It is currently defined by RFC 1350.
There have been some extensions to the TFTP protocol documented in
later RFCs.. TFTP is based in part
on the earlier protocol EFTP, which was part of the PUP protocol suite. TFTP support appeared first as part of 4.3 BSD.
Due to the lack of security, it is dangerous to use it over the
Internet. Thus, TFTP is generally only used on private, local networks.
Note
If a TFTP server is not available on your Linux distribution or installed system, you can obtain
a binary version for most Linux distributions from
http://www.rpmfind.net/linux/rpm2html/ by
searching for the string
tftpd.
Ubuntu and Debian users can install the TFTP server with the following command:
# apt-get install xinetd tftpd
Before configuring the TFTP daemon itself, make sure that the entries for the TFTP protocol are not
commented out in the
/etc/services file. This file is typically consulted
by each network service in order to determine the network ports that it should use.
You must be the root user to edit this file. Use your favorite text editor to remove the comment character
(
#) from the beginning of each line that contains the string
tftp. Active
TFTP entries in
/etc/services should look like the following:
tftp 69/tcp
tftp 69/udp
Depending on the desktop Linux distribution and version you are using, Linux systems typically use
one of two mechanisms to activate and manage network servers such as TFTP servers. These are either
the
Internet Services Daemon (inetd) or, more commonly, the
Extended Internet Services
Daemon (xinetd). Both of these commands manage a variety of network services by monitoring various
network ports and starting the appropriate daemon in response to a valid request. The more modern
mechanism is
xinetd, and it is generally viewed as being more secure than the older
inetd.
To determine which of these mechanisms your system uses to manage Internet services, you can use the
system’s
ps (process status) command, as in the following example:
# ps -alxww | grep inet
140 0 578 1 0 0 1152 356 do_select S ? 0:00 xinetd ...
0 500 13361 13336 18 0 1360 508 pipe_read S ? 0:00 grep -i inet
In this example, the system is using the
xinetd server, and you should follow the
instructions in
Configuring a TFTP
Server Run by xinetd. If the output from this command shows that your system is running the
inetd server,
proceed to
Configuring a TFTP Server
Run by inetd.
Configuring a TFTP Server Run by xinetd
The servers that can be managed by the
xinetd daemon are each listed in a server-specific
configuration file located in the directory
/etc/xinetd.d. The file
for the TFTP server is named
tftp, and looks like the following:
# default: off
# description: The tftp server serves files using the Trivial File Transfer \
# Protocol. The tftp protocol is often used to boot diskless \
# workstations, download configuration files to network-aware printers, \
# and to start the installation process for some operating systems.
service tftp
{
socket_type = dgram
protocol = udp
wait = yes
user = root
server = /usr/sbin/in.tftpd
server_args = -s /tftpboot
disable = yes
}
To enable the TFTP server, edit this file as the root user, replacing the word
yes on
the
disable line with the word
no.
Then save the file and exit the editor.
Next, restart the
xinetd process to force it to reread its configuration files, as
described in
Restarting the Service
Restarting the Service
If your system is running a desktop Linux distribution such as Red Hat Linux, which starts and stops
system processes by using
run configuration (rc) scripts, you can simply restart the daemon
by invoking these scripts in one of the following commands that is appropriate for your daemon:
# /etc/init.d/xinetd restart
# /etc/init.d/inetd restart
This command will stop and then restart all of the services managed by the daemon on your Linux system.
In addition to the
restart command, you can also issue
stop and
start commands
this way.
Caution
If your Linux system is running Internet services on which other systems depend, restarting the
daemon will cause a slight interruption in those services.
After executing this command, the TFTP server will be started on your system in response to incoming
TFTP requests, and you can access any files you copied to
/tftpboot.
Note
If you need another way to stop the process, the following method will work on any Linux distribution.
Send the HUP signal to the running
xinetd process. To do this, you must first
determine the process ID of the process that is currently running on your system by using the
ps process
status command, as in the following example:
# ps -alxww | grep xinet
140 0 578 1 0 0 1152 356 do_select S ? 0:00 xinetd
0 500 13361 13336 18 0 1360 508 pipe_read S ? 0:00 grep -i xinet
Of course, substitute
inetd if that is the service you are using.
The
-alxww options to the
ps command cause it
to display all system processes in an extremely wide listing. The
grep command
then searches for the string
xinet in the resulting listing. This example displays information
about a running command whose name or arguments contain the string
xinet.
Of these, the first is the actual
xinetd process, and the third field is its
process ID (in this example, 578). The process ID is the information that you will need to restart
the process.
After collecting this information, you can cause the
xinetd process to reread
its configuration file by executing a command like the following:
# kill -HUP 578
Testing the Service
To ensure the TFTP server is running place a small text file in /tftpboot:
# echo "Hello, embedded world" > /tftpboot/hello.txt"
Then execute the following commands:
# tftp localhost
tftp> get hello.txt
Received 23 bytes in 0.1 seconds
tftp> quit
