copy files from tftp server

Question

AFAIU, When tftp server is used for pxe booting, the client sends a request to the server, and the server sends back few files (initrd, kernel, config, ...). The server can decide which files to send to the client depending on the IP address of the client. The client does not know the URL of those files.

My questions is this:

I would like to test tftp server. I would like to run a command, or a (simple) script which contacts the tftp server, and receives the files, and saves these files on the disk.

In other word what I want to do is this:

• On the server side, there is no difference: the server thinks the client wants to boot over PXE and sends the files to the client

• On the client side: the client does not actually want to boot. It just wants to copy (save) the files to disk.

What would be the easiest way to do this?

Answer 1

The comment @Patrick made to your question was dead right: all the client machine needs to bootstrap PXE is to broadcast a DHCP request. The DHCP server (usually on the PXE boot server) will see the MAC address of the client device and will use it to

• give the client an IP address
• tell the client what files it should get from the PXE server

at that point, the client knows the address of the server and what to get from it. Unfortunately, there are a bunch of fiddly bits like there can be only one DHCP server which has the special configuration for the PXE client, a TFTP server needs to be running and so on.

There is a pretty good step by step guide at https://wiki.debian.org/PXEBootInstall. You didn't specify your distro, but most PXE systems will at least rhyme with that guide.

I know that your question says you don't want to know the address of the PXE server. But there is only one way (without writing your own client) that can be done, with a PXE client DHCP requester/processor. If you want to forego that part you throw away much of the capabilites needed to get you bootstrapped.

I know that you don't actually want to boot the machine which puts you in the position of implementing a lot of the PXE protocol for testing purposes. If you don't have a scratch machine available, I'm curious as to why you need to test PXE at all.

Answer 2

How about using a real tftp client?

Those two which come to my mind:

• tftp
• atftp

Answer 3

I'm most familiar with how Cobbler sets up TFTP so I'm not sure if this is relevant but I'll offer this info up anyway. Cobbler sets up a bootloader using pxelinux.0 as @Patrick explains in the comments as well as @msw. But it also sets up a corresponding pxelinux.cfg/ directory along side it that contains MAC addresses for each system that will be connecting to the server.

These files contain pxelinux.cfg file info like this:

$ more 01-54-52-00-ff-ff-ff
default linux
prompt 0
timeout 1
label linux
        kernel /images/Centos56-x86_64/vmlinuz
        ipappend 2
        append initrd=/images/Centos56-x86_64/initrd.img ksdevice=bootif lang=  console=ttyS0,115200 text serial kssendmac  ks=http://192.168.1.207/cblr/svc/op/ks/system/kvmcobblertest

The actual Linux kernel that this VM will boot is contained in this TFTP accessible directory, /images/Centos56-x86_64/vmlinuz. The entire TFTP directory structure looks like this from the backside of the server:

$ ls -l /tftpboot/
total 348
drwxr-xr-x 2 root root   4096 Jun 22  2011 etc
drwxr-xr-x 2 root root   4096 Jul  9  2012 grub
drwxr-xr-x 6 root root   4096 Jul  9  2012 images
drwxr-xr-x 2 root root   4096 Jun 30  2011 images2
-rw-r--r-- 1 root root  20020 Jul  9  2012 memdisk
-rw-r--r-- 1 root root  39188 Jul  9  2012 menu.c32
drwxr-xr-x 2 root root   4096 Jun 22  2011 ppc
-rw-r--r-- 1 root root  14716 Jul  9  2012 pxelinux.0
drwxr-xr-x 2 root root   4096 Jul  9  2012 pxelinux.cfg
drwxr-xr-x 2 root root   4096 Jul  9  2012 s390x
-rw-r--r-- 1 root root 198192 Jul  9  2012 yaboot

The only thing that's initially accessible by the servers that are booting against this TFTP server, is as other's have described, the pxelinux.0 + the configuration file that corresponds to a particular server's MAC address.

Images directory

This looks like this if you're curious:

$ tree /tftpboot/images
/tftpboot/images
|-- Centos56-x86_64
|   |-- initrd.img
|   `-- vmlinuz
|-- Centos56-xen-x86_64
|   |-- initrd.img
|   `-- vmlinuz
`-- Centos60-x86_64
    |-- initrd.img
    `-- vmlinuz

3 directories, 6 files