PXEBOOT(8)

NAME
pxeboot - network boot NetBSD/i386 through a PXE BIOS extension

DESCRIPTION
pxeboot is a NetBSD boot program running on top of a PXE BIOS extension which is provided by the motherboard or a plug-in network adapter, in accordance with the Intel Preboot eXecution Environement (PXE) specification.

Network booting a system through PXE is a two-stage process:

1.  The PXE BIOS issues a DHCP request and fetches the NetBSD pxeboot program using TFTP.

2.  The NetBSD pxeboot program takes control. An interactive mode is entered if the user presses a key within five seconds. After this time or after the user's boot command, another DHCP request is issued and the kernel is loaded as specified in the DHCP reply. To read the kernel file, the NFS (version 2) or TFTP protocols can be used.

The DHCP request issued by the NetBSD pxeboot program has the following special parameters:

Bootfile name
    is set to the filename argument on the boot command line typed in by the user (can be empty), or to “netbsd” in the non-interactive case.

DHCP Vendor class identifier tag
    is set to “NetBSD:i386:libsa”.

The DHCP server can use these fields to distinguish between the various originators of requests (first and second PXE stage, NetBSD kernel), and to control conditional behaviour depending on the user's command line input to the pxeboot program, e.g. to support alternative NetBSD installations on one machine.

In addition to the standard network interface configuration, the following fields in the DHCP reply are interpreted:

Bootfile name
    specifies the protocol to be used, and the filename of the NetBSD kernel to be booted, separated by a colon. Available protocols are “nfs” and “tftp”. The kernel filename part is interpreted relatively to the NFS root directory (see the Root path reply field below) or the TFTP server's root directory (which might be a subdirectory within the TFTP server's filesystem, depending on the implementation), respectively. If the Bootfile name field replied by the DHCP server does not contain a colon, it is ignored, and the filename typed in at the pxeboot command line prompt (or the “netbsd” default, see the section about the Bootfile name field in the DHCP request above) is used. If no protocol was specified, “nfs” is assumed.

Swap server
    can be used to override the “server IP address” if NFS is used to access the kernel. This matches the behaviour of the NetBSD kernel to access its root file system on NFS. This way, different TFTP and NFS servers can be communicated to the DHCP client ( it is actually a deficiency of the DHCP protocol to provide a “root path” field but no corresponding IP address).

Root path
    is used as path to be mounted in the NFS case to access the kernel file, matching the NetBSD kernel's behaviour.

The commands accepted in interactive mode are:

boot
    [device:] [filename] [-1234abcdmqsvxz] Boot NetBSD. See boot in boot(8) for full details.

help
    Print an overview about commands and arguments.

quit
    Leave the pxeboot program.

By default the output from pxeboot and from the booted kernel will go to the system's BIOS console. This can be changed to be one of the serial ports by using installboot to modify the boot options contained in the pxeboot_ia32.bin file.

FILES

/usr/mdec/pxeboot_ia32.bin

EXAMPLES
The first /etc/dhcpd.conf example shows a simple configuration which just loads a file “netbsd” from the client's NFS root directory, using the defaults for protocol and kernel filename. Similar setups should be possible with any BOOTP/DHCP server.

    host myhost {
        hardware ethernet 00:00:00:00:00:00;
        fixed-address myhost;
        option host-name "myhost";
        filename "pxeboot_ia32.bin";
        option swap-server mynfsserver;
        option root-path "/export/myhost";
    }

The following /etc/dhcpd.conf entry shows how different system installations can be booted depending on the user's input on the pxeboot command line.

    host myhost {
        hardware ethernet 00:00:00:00:00:00;
        fixed-address myhost;
        option host-name "myhost";
        if substring (option vendor-class-identifier, 0, 9) = "PXEClient" {
            filename "pxeboot_ia32.bin";
        } elsif filename = "tftp" {
            filename "tftp:netbsd.myhost";
        } else {
            option swap-server mynfsserver;
            option root-path "/export/myhost";
            if filename = "generic" {
                filename "nfs:gennetbsd";
            } else {
                filename "nfs:netbsd";
            }
        }
    }

It is assumed that the TFTP server is the same as the DHCP server unless a next-server directive is specified somewhere else in dhcpd.conf, and that the NFS server for the root file system is mynfsserver. The swap-server:root-path is only used in the NFS case and by the NetBSD kernel to mount the root file system.

SEE ALSO
boot(8), dhcpd(8), diskless(8), installboot(8) Preboot Execution Environment (PXE) Specification, Version 2.1, September 20, 1999, Intel Corporation.

HISTORY
The NetBSD/i386 pxeboot command first appeared in NetBSD 1.6.

BUGS
If an error is encountered while reading the NetBSD kernel file or if its file format wasn't recognized, it is impossible to retry the operation because the PXE network stack is already removed from the system RAM.

You need the pxeboot from an i386 build to boot an i386 kernel, and that from an amd64 build to boot an amd64 kernel.