Installing TFTP-HPA and PXELinux

Keep in mind that you should only have a single DHCP server running on a given network. If you setup an additional DHCP server on a single network, it is extremely likely that you will break DHCP for ALL systems on that network. Make sure that you know your network’s layout, and whether or not there’s an existing DHCP server running.

If you just want to experiment with this stuff, get yourself a hefty workstation with lots of RAM (2-4GB), a decent processor (anything current will do), and a lot of disk space (a typical Fedora Core installation requires about 4GB of disk, and you’ll want some extra room to store your installation media, so at least 15GB should do the trick), and use VirtualBox (or VMWare Workstation/Fusion/Server) to setup a virtual machine running Linux. This system can then be used as a DHCP and TFTP server for a private network within VirtualBox, thus isolating your environment from the rest of the network. You can then create a second virtual machine that can be used as your PXE client.

If you’re looking to implement this on a corporate network, be sure to ask your network administrator(s) for permission beforehand. In addition to ensuring that it’s ok to implement, your network administrator will very likely have good advice for how to set this sort of thing up – and, even if they don’t, at least they’ll know what’s going on when all hell breaks loose because the DHCP server has stopped responding or has started handing out invalid leases…

In a hurry? Take a look at the TFTP summary instead.

Install tftpd-hpa by running:

emerge -av tftp-hpa

You’ll want to either edit /etc/conf.d/in.tftpd, where the -s parameter equates with INTFTPD_PATH. Note that you’ll have to add the -m parameter to the INTFTPD_OPTS value. You’ll also need to run:

rc-update add in.tftpd default

…or do it the lazy way and just add the entire command line to /etc/conf.d/local.start like so:

/usr/sbin/in.tftpd -s /var/lib/tftpboot -m /var/lib/tftpboot/pxelinux.cfg/remap

Install tftpd-hpa by running:

apt-get install tftpd-hpa

Edit /etc/xinetd.d/tftp (or create it if it doesn’t exist), using the following as a guide:

service tftp
{
    disable = no
    wait = yes
    user = root
    socket_type = dgram
    protocol = udp
    server = /usr/sbin/in.tftpd
    server_args = -m <remapping rules file> -s <TFTP server root>
}

For other distributions, simply install xinetd and tftpd-hpa however you like, and use the Ubuntu xinetd configuration file above.

If you’re running tftp-hpa on a Linux system, you have to keep in mind the fact that most (if not all) Linux filesystems are case-sensitive (unlike Windows filesystems like FAT16/32 or NTFS). If you’re planning on installing Windows over the network using the Microsoft Deployment Toolkit (which I highly recommend using if you want to install Windows with ease), then you’ll eventually run into the fun fact that Microsoft’s Windows PE bootloader uses hard-coded, mixed-case filenames and paths inconsistently during the PXE boot process. This tiny little niggle caused me nearly a week’s worth of headaches and swearing before I found a simple work-around: tftp-hpa’s file remapping feature. The only problem that I had was that it’s not very well documented, and the few examples I could find online were uniformly over-complicated.

Here’s the simplest solution that I could come up with:

1. create /var/lib/tftpboot/pxelinux.cfg/remap using your favorite text editor, with the following contents:

   rg \\ /
   rg ([A-Z]) \L\1
   

2. modify the command-line arguments for tftpd-hpa to include -m /var/lib/tftpboot/pxelinux.cfg/remap.
3. ensure that all of the files and folders below /var/lib/tftpboot/ are lower-case, rather than mixed- or upper-case. You can use this bash script to do this quickly and easily, once you have all of your files in place (or whenever you add new files to the tree) – just ignore any of the warnings (and there will be a warning for each file that’s already lower-case):

   for i in `find /var/lib/tftpboot/ -type d && find /var/lib/tftpboot/ -type f`; do
         mv $i `echo $i | tr [:upper:] [:lower:]`
   done

The TFTP remap file tells tftp-hpa to:

1. rg \\ /: replace backslashes (\) in the requested filename with forward-slashes (/); this is really only useful if your TFTP server is running on Linux, where the path separator is the forward-slash. If you were running this on Windows, you would need to use rg / \\ instead;
2. rg ([A-Z]) \L\1: replace any uppercase letters in the requested filename with the lowercase version instead. This avoids the problem of case-sensitivity in Linux filesystems; again, this is only needed if the TFTP server root is located on a case-sensitive filesystem (like ext2/ext3/reiserfs), and is probably unnecessary on a Windows TFTP server.

Most of the solutions I’ve found on other websites have an entry per file, which I figure will eventually be unmaintainable as you add boot images to the TFTP server. The above solution requires no maintenance, as long as you ensure that all of your files and folders under /var/lib/tftpboot/ are lowercase.

I typically save my remap file as /var/lib/tftpboot/pxelinux.cfg/remap, so that if I ever need to move my TFTP server somewhere, I can just zip up the entire /var/lib/tftpboot tree.

Install PXELinux by running:

emerge -av syslinux

The files you need will be located in /usr/share/syslinux/. Copy or symlink the files to your TFTP server root directory.

Install PXELinux by running:

apt-get install syslinux

The files you need will be located in /usr/lib/syslinux.

The version of Syslinux included in most Linux distributions tends to lag extremely far behind the official releases, so you’ll likely want to download a copy instead. Note that you don’t need to compile the syslinux release on your own: precompiled binaries are included in the release, so you’ll just need to download and extract the latest release to a temporary folder, and copy the appropriate files to your TFTP server’s root directory.

Ubuntu is almost always significantly out of date (3.53 at the time of writing), while Gentoo is fairly up to date (version 3.73 at the time of writing). Currently, 3.80 has only been available for about two weeks.

The instructions I’ll provide for configuring PXELinux using vesamenu.c32 will NOT work with the current Ubuntu package. You will need at least version 3.73 for my instructions to work, but if you don’t care about the fancy menu capabilities provided by vesamenu.c32, you’ll be fine using the Ubuntu package.