PXE boot
Brett Lee
=====================================================================


-------------------------------------------------------
** Other document briefs in this directory:

     pxeboot-Kickstart (Installing over the network)
     pxeboot-NFS (Running a NFS root filesystem)
     pxeboot-Rescue (Boot a rescue image)
-------------------------------------------------------



Get pxelinux.0 and put it in the root of the tftp server dir.

Example:
     /tftpboot/pxelinux.0


Configure dhcpd.conf:

  If TFTP server is a different host than DHCP server, specify this using 
  the "next-server" option.

     Example:
     next-server linux.home.local;      # TFTP server

  Set the "filename" option to pxelinux.0 

     Example:
     filename "pxelinux.0";               # The file



Enable PXE boot on the client.

  Usually this means configuration via the BIOS, or by interrupting
  the boot process, but there also may be additional configuration
  within the Boot ROM.

    For example, the Broadcom Boot ROM has a (CNTL-S) to config.


Overview:

  Client boots, performs a DHCPDISCOVER (possibly BOOTP) and waits for a
  DHCPOFFER that includes the "filename" parameter.

  IP an address gets assigned, system checks for a next-server param, tries to
  get the PXE file from /tftpboot/pxelinux.0, and if sucessful executes it.

  pxelinux.0 helps find the kernel, rootfs, initrd and other params to boot.


pxelinux.0:

  After the client boots, it will attempt to find it's PXE-specific "config" file.
  The config file is named per the MAC address and exists relative to the
  pxelinux.0 file.  If you placed pxelinux.0 in /tftpboot, you should have a
  file/directory structure under /tftpboot/pxelinux.cfg/ containing some files.
  In the example below, the MAC address of the booting device is 00:30:48:5C:61:3E
  so to get the PXE specific one you would need to prepend a "01" to the MAC.

  If the MAC specific file is not found, a file with the HEX of the IP address
  is checked.

  [root@linux ~]# gethostip 192.168.0.55
  192.168.0.55 192.168.0.55 C0A80037
  [root@linux ~]#

  If that is not found, subsequent checks are made minus each nibble.  Lastly,
  a default file is checked.

Example:
     /tftpboot/pxelinux.cfg/01-00-30-48-5C-61-3E
     /tftpboot/pxelinux.cfg/C0A80037
     /tftpboot/pxelinux.cfg/C0A8003
     /tftpboot/pxelinux.cfg/C0A800
     /tftpboot/pxelinux.cfg/C0A80
     /tftpboot/pxelinux.cfg/C0A8
     /tftpboot/pxelinux.cfg/C0A
     /tftpboot/pxelinux.cfg/C0
     /tftpboot/pxelinux.cfg/C
     /tftpboot/pxelinux.cfg/default


What might go in the file?  The information needed to boot: 

[root@linux pxelinux.cfg]# cat 01-00-30-48-5C-61-3E
DEFAULT linux
LABEL linux
SAY Now booting the kernel from SYSLINUX for: SuperMicro_1
KERNEL vmlinuz
APPEND text ro root=/dev/sda1 initrd=initrd.img
[root@linux pxelinux.cfg]#



Given the above configuration, initrd.img and the vmlinuz kernel will need
to be on tftp server.  Put them in the root alongside pxelinux.0.

-rw-r--r--    1 root     root      5669675 Nov 14 10:46 initrd.img
-rw-r--r--    1 root     root        13148 Nov 14 10:51 pxelinux.0
drwxr-xr-x    2 root     root         4096 Nov 14 16:51 pxelinux.cfg
-rw-r--r--    1 root     root      1806388 Nov 14 10:41 vmlinuz



Sample /etc/dhcpd.conf entries:

   # Boot and install CentOS on these guys
   group {

     allow bootp;
     allow booting;

     option ip-forwarding    false;  # No IP forwarding
     option mask-supplier    false;  # Don't respond to ICMP Mask req

     min-lease-time 300;                   # 60     - 1 min
     default-lease-time 300;               # 86400  - 1 day
     max-lease-time 300;
     use-host-decl-names on;

     next-server linux.home.local;         # TFTP server
     filename "pxelinux.0";                # The file

     host superm1 {
       hardware ethernet     00:0c:29:ca:b7:28; # left  - Intel
     # hardware ethernet     00:0c:29:ca:b7:29; # right - Broadcom
       fixed-address         192.168.1.201;
     }
   }



Now just reboot and see if it boots.  For booting to Kickstart an install,
running an NFS root filesystem, or booting a rescue image, please see the other
files in this directory.


Additional references:
http://myhowtosandprojects.blogspot.com/2008/07/pxe-magic-boot-os-from-network-with_01.html