[syslinux] Baking Cookies

Santillanes, Russel Russel.Santillanes at gs.com
Wed Nov 20 13:11:34 PST 2013

I think my oven is broken, but maybe I have the recipe wrong.

I've been trying to utilize the lwIP stack and dmi information to avoid iPXE use. I can do a SYSAPPEND 0x00080 and it shows up in /proc/cmdline after booting the kernel, but tcpdump is not revealing the cookies as described during HTTP calls in the documentation.

Trying the magic "SENDCOOKIES" parameter outside of an inline SYSAPPEND  call just gives me an "Error: An undefined symbol was referenced"

I'm using 6.02 and lpxelinux.0; Loading lpxelinux.0 over tftp, kernel/initrd over http (see below)

My default file looks like this:

Label <some label>
        KERNEL http://path.to.kernel/vmlinuz0
        APPEND <some flags> initrd=http://path.to.initrd/initrd0.img
        SYSAPPEND 0x1FFF0

This gives me all the magic DMI information on boot in /proc/cmdline, but I'm not getting any Cookie data, just this in the headers:

User-Agent: Syslinux/6.02
Connection: close

I'm supposed to get cookies, per this line in syslinux.txt - but cant figure out where to put it in the config file to have it be accepted.

SENDCOOKIES bitmask        [PXELINUX only]

   When downloading files over http, the SYSAPPEND strings are
   prepended with _Syslinux_ and sent to the server as cookies.
   The cookies are URL-encoded; whitespace is *not* replaced with

   This command limits the cookies send; 0 means no cookies.  The
   default is -1, meaning send all cookies.

   This option is "sticky" and is not automatically reset when
   loading a new configuration file with the CONFIG command.


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