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Setting up a TFTP Server

Once U‑Boot has been loaded onto the target system it may retrieve a memory image via a TFTP server. This section will describe how to setup a TFTP server under SuSE Linux as well as Windows and how to use this server to load uClinux via U‑Boot.

Before a host (either Linux or Windows) can be used as a tftp server, whatever firewall you may be running must be set to allow the host to accept traffic on port 69. It will not work if port 69 is blocked.

Optimizing your tftp server

TFTP supports an optional Blocksize option. (see RFC 2348. This can help decrease download times on slow networks. To see how much, and experiment was run to measure tftp throughput on a slow network (U-Boot client running in USA, tftp server in Germany).

tftpblocksize download
(bytes) (ms)
512 default 48,246
1468 ( 1MTU) 17,243
2948 ( 2MTU) 8,912
4428 ( 3MTU) 6,167
5908 ( 4MTU) 4,840
7388 ( 5MTU) 4,042
8868 ( 6MTU) 3,425
10348 ( 7MTU) 2,974
11828 ( 8MTU) 2,736
13308 ( 9MTU) 2,508
14788 (10MTU) 2,281
16268 (11MTU) 2,174

So, that is 48-seconds (default, if your tftp server does not support RFC 2348), to either 17 (1 max packet size), or 2 seconds, if your U-Boot supports packet re-assembly or defragmentation.

However, it appears that some tftp servers (the older BSD version, Debian's “tftpd”) doesn't support RFC 2348 (blksize), and always use a block size of 512, causing the traffic to slow down. :( You need to make sure that you install the the Peter Anvin version, which does support RFC 2348, and blksize up to 65,464 bytes (Debian's “tftpd-hpa”). This can be found on this Web site.

How to tell which you have? Check your man page: ”man tftpd” or ask for the version:

Peter Anvin version:

 rgetz@imhotep:~> /usr/sbin/in.tftpd -V
tftp-hpa 0.48, with remap, with tcpwrappers

non-RFC 2348 one:

rgetz@imhotep:~> /usr/sbin/in.tftpd -V

Even when using the Peter Anvin version, block size can still be reduced via two methods:

limits the maximum permitted block size (-B 512)
rejects RFC 2347 TFTP options (-r blksize) Check your local /etc/xinetd.d/tftp or /etc/inetd.conf file to see how your tftpd server is being invoked.

System Specifics

Debian Linux Instructions

  1. Install tftpd-hpa and related packages.
    $ sudo apt-get install xinetd tftpd-hpa tftp
  2. Check you have things installed:
    user@machine:~ $ /usr/sbin/in.tftpd -V
    tftp-hpa 0.36, with remap, with tcpwrappers
  3. Create /etc/xinetd.d/tftp and put this entry:
    service tftp
    protocol        = udp
    socket_type     = dgram
    wait            = yes
    user            = root
    server          = /usr/sbin/in.tftpd
    server_args     = -s /tftpboot
    disable         = no
  4. Make /tftpboot directory
    $ sudo mkdir /tftpboot
    $ sudo chmod -R 777 /tftpboot
    $ sudo chown -R nobody /tftpboot
  5. Start tftpd through xinetd
    $ sudo /etc/init.d/xinetd start

SuSE Linux Instructions

The procedure for setting up a TFTP server under SuSE Linux is given below. For other distributions of Linux this procedure may differ slightly. You may have to install TFTP if it is not already installed on your system.

Setting up from command line

First, as root, make a directory to store the uClinux image which will be loaded onto the target system.

bash# mkdir /tftpboot

Next the ownership of this directory must be changed to nobody as this is the default user ID setup by tftpd. It is also a good idea to give world write permission to this directory, to allow normal users (not root) to copy files for downloading.

bash# chown nobody:nobody /tftpboot
bash# chmod 777 /tftpboot

Next move the image of a compiled version of uClinux into the tftpboot directory. This file is usually named linux. For more information on compiling uClinux see Compiling the Kernel.

Now the file /etc/xinetd.d/tftp must be edited to match the following:

service tftp
   socket_type  =  dgram
   protocol     =  udp
   wait         =  yes
   user         =  root
   server       =  /usr/sbin/in.tftpd
   server_args  =  -s /tftpboot
   disable      =  no		

Under SuSE Linux 9.0 the following options needed to be changed from their default values:

disable = no (enables the TFTP service)
server_args = -s /tftpboot (sets the directory to /tftpboot

Next, to start the TFTP server enter the following command as root:

bash# /etc/init.d/xinetd restart

Using the Suse GUI

Alternately the TFTP server may be enabled through the XWindows interface. These instructions are for SuSE Linux 9.0. For other distributions of Linux this procedure may vary.

Open the Control Center which is located under the start menu. The Control Center window should now be displayed:

Click on YaST2 modules.

The YaST2 modules sub-menu should now be displayed in the sidebar:

Click on Network Services.

The Network Services sub-menu should now be displayed in the sidebar:

Click on TFTP Server then click the Administrator Mode button (you will need the root password).

After entering the root password the TFTP server configuration module should now be displayed:

Select the Enable radio button.

Enter /tftpboot in the Boot Image Directory textbox.

Click Finish.

Windows Instructions

There are several TFTP server programs available for the Windows platform. The setup instructions in this section are for the program TFTP Turbo. TFTP Turbo is available free of charge from Weird-solutions. The setup procedure for other TFTP server programs will differ.

First, download the installer program for TFTP Turbo and run it. Follow the instructions given to install TFTP Turbo, select a full installation. Once installation is complete start TFTP Turbo. The TFTP Turbo main window should now be displayed:

Double Click on localhost in the Servers sidebar

The login dialog should now be displayed:

Leave the Password field blank and click on Login

With localhost still selected, under the Edit menu select Properties. The Server Properties dialog should now be displayed:

In the Virtual Root field enter the path to the directory you wish to use as the TFTP root directory.

In this example C:\tftpboot is used. Ensure that a valid uClinux kernel image exists in this directory.

Next, with localhost still selected, under the Tools menu select Control Service. The Control Service dialog should now be displayed:

If the message says ”TFTP Turbo is running on localhost” simply click OK.

If the message says ”TFTP Turbo is not running on localhost” click Start then click OK.

The TFTP Turbo server should now be running.

Testing TFTP

The first step in testing tftp is to check if local access works.

  1. see if things are running:
    blackfin@linux 0 ~ $ netstat -l -u | grep ftp
    udp        0      0 *:tftp
  2. create a file foo in the /tftpboot directory.
    blackfin@linux 0 ~ $ touch /tftpboot/foo
  3. see if you can grab the file:
    blackfin@linux 0 ~ $ tftp localhost
    tftp> get foo
    tftp> quit
    blackfin@linux 0 ~ $ ls -l foo
    -rw-r--r--  1 blackfin users 0 2006-07-31 09:49 foo
  4. see if you can download the file via the external network:
    blackfin@linux 0 ~ $ /sbin/ifconfig  | grep "inet addr"
              inet addr:  Bcast:  Mask:
              inet addr:  Mask:
    blackfin@linux 0 ~ $ tftp
    tftp> get foo
    tftp> quit
    blackfin@linux 0 ~ $ ls -l foo
    -rw-r--r--  1 blackfin users 0 2006-07-31 09:49 foo
  5. see if you can download the file via a different machine

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