xref: /netbsd-src/share/man/man8/man8.x86/pxeboot.8 (revision 9aa5e65867d65343760f3c01c8d8d032aba94b7a)

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.\" Copyright (c) 2003
.\" 	Matthias Drochner.  All rights reserved.
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.Dd February 17, 2017
.Dt PXEBOOT 8 x86
.Os
.Sh NAME
.Nm pxeboot
.Nd network boot NetBSD/x86 through a PXE BIOS extension
.Sh DESCRIPTION
.Nm
is a
.Nx
boot program running on top of a
.Tn PXE
.Tn BIOS
extension which is
provided by the motherboard or a plug-in network adapter,
in accordance with the
.Tn Intel
Preboot eXecution Environment
.Pq Tn PXE
specification.
.Pp
By default, the
.Nm
program is configured with modules loading and
.Xr boot.cfg 5
support disabled.
See
.Sx EXAMPLES
for how to enable these options individually.
This manual page assumes that
.Xr boot.cfg 5
support is enabled.
.Pp
Network booting a system through
.Tn PXE
is a two-stage process:
.Pp
.Bl -enum
.It
The
.Tn PXE
.Tn BIOS
issues a
.Tn DHCP
request and fetches the
.Nx
.Nm
program using
.Tn TFTP .
.It
The
.Nx
.Nm
program takes control.
It immediately issues another
.Tn DHCP
request to get the name of a
.Xr boot.cfg 5
file to load, using
.Dq boot.cfg
by default.
If the boot config file is not found, or if the supplied file appears
not to be a boot configuration file, the file is skipped.
Otherwise it is loaded and obeyed as described in
.Xr boot.cfg 5 .
If a boot configuration is not loaded, the user has the option to
enter a limited version of the standard interactive boot mode by
pressing a key within five seconds.
After this time, or after the user's
.Ic boot
command, another
.Tn DHCP
request is issued and the kernel filename returned by the
.Tn DHCP
reply, using
.Dq netbsd
by default,
is loaded.
To read the kernel file, the
.Tn NFS
.Pq version 2
or
.Tn TFTP
protocols can be used.
.El
.Pp
The
.Tn DHCP
request issued by the
.Nx
.Nm
program has the following special parameters:
.Bl -tag -width xxxx
.It Bootfile name
is set to
.Dq boot.cfg
during the first request, and then to
the
.Va filename
argument on the
.Ic boot
command line typed in by the user (can be empty), using
.Dq netbsd
in the non-interactive case.
.It DHCP Vendor class identifier tag
is set to
.Dq NetBSD:i386:libsa .
.El
.Pp
The
.Tn DHCP
server can use these fields (i.e. the
.Tn DHCP
vendor class identifier tag and the requested file name, possibly
supplied by the user's command line input to the
.Nm
program) to distinguish between the various originators of requests
(PXE BIOS, first and second
.Nm
stage,
.Nx
kernel), and to alter its behaviour.
For example, this can be used to support alternative
.Nx
installations on one machine.
.Pp
In addition to the standard network interface configuration,
the following fields in the
.Tn DHCP
reply are interpreted:
.Bl -tag -width xxxx
.It Bootfile name
specifies the protocol to be used, and the filename of the
boot config or
.Nx
kernel to be booted, separated by a colon.
Available protocols are
.Dq nfs
and
.Dq tftp .
The boot config or kernel filename part is interpreted relatively to
the NFS root directory (see the
.Em 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
.Em Bootfile name
field replied by the DHCP server does not contain a colon,
it is ignored, and the
.Va filename
typed in at the
.Nm
command line prompt (or the
.Dq netbsd
default, see the section about the
.Em Bootfile name
field in the DHCP request above) is used.
If no protocol was specified,
.Dq nfs
is assumed.
.It Next server
is used as the location of the tftp server.
.It Swap server
can be used to override the
.Dq server IP address
if
.Tn NFS
is used to access the kernel.
This matches the behaviour of the
.Nx
kernel to access its root file system on
.Tn NFS .
This way, different
.Tn TFTP
and
.Tn NFS
servers can be communicated to
the
.Tn DHCP
client
.Po
it is actually a deficiency of the
.Tn DHCP
protocol to provide a
.Dq root path
field but no corresponding IP address
.Pc .
.It Root path
is used as path to be mounted in the
.Tn NFS
case to access the kernel file, matching the
.Nx
kernel's behaviour.
.El
.Pp
See
.Xr x86/boot 8
for the commands accepted in interactive mode.
.Pp
By default the output from
.Nm
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
.Nm installboot
to modify the boot options contained in the
.Pa pxeboot_ia32.bin
file.
.Sh FILES
.Bl -tag -width /usr/mdec/pxeboot_ia32.bin
.It Pa /usr/mdec/pxeboot_ia32.bin
.El
.Sh EXAMPLES
To enable
.Xr boot.cfg 5
support in the
.Nm
program:
.Bd -literal -offset indent
installboot -e -o bootconf pxeboot_ia32.bin
.Ed
.Pp
To enable modules loading support in the
.Nm
program:
.Bd -literal -offset indent
installboot -e -o modules pxeboot_ia32.bin
.Ed
.Pp
The first
.Pa /etc/dhcpd.conf
example shows a simple configuration which just loads
.Dq boot.cfg
and
.Dq 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.
.Pp
.Bd -literal
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";
}
.Ed
.Pp
The following
.Pa /etc/dhcpd.conf
entry sets loads the boot config and kernel over tftp.
This can be used, for example, for installing machines by using
an install kernel.
.Pp
.Bd -literal
host myhost {
    hardware ethernet 00:00:00:00:00:00;
    fixed-address myhost;
    option host-name "myhost";
    next-server mytftpserver;

    # This section allows dhcpd to respond with different answers
    # for the different tftp requests for the bootloader and kernel.
    if substring (option vendor-class-identifier, 0, 20)
      = "PXEClient:Arch:00000" {
        filename "pxeboot_ia32.bin";
    } elsif substring (option vendor-class-identifier, 0, 17)
      = "NetBSD:i386:libsa" {
        if filename = "boot.cfg" {
            filename "tftp:boot.cfg";
        } else if filename = "netbsd" {
            filename "tftp:netbsd-INSTALL.gz";
        }
    }
}
.Ed
.Pp
The following
.Pa /etc/dhcpd.conf
entry shows how different system installations can be booted depending on
the user's input on the
.Nm
command line.
.Pp
.Bd -literal
host myhost {
    hardware ethernet 00:00:00:00:00:00;
    fixed-address myhost;
    option host-name "myhost";
    next-server mytftpserver;
    if substring (option vendor-class-identifier, 0, 9) = "PXEClient" {
        filename "pxeboot_ia32.bin";
    } elsif filename = "boot.cfg" {
        filename "tftp:boot.cfg";
    } 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";
        }
    }
}
.Ed
.Pp
The
.Tn TFTP
server is supplied using the
.Em next-server
directive.
The
.Tn NFS
server for the root file system is
.Em mynfsserver .
The
.Em swap-server:root-path
is only used in the
.Tn NFS
case and by the
.Nx
kernel to mount the root file system.
.Sh SEE ALSO
.Xr boot.cfg 5 ,
.Xr dhcpd 8 ,
.Xr diskless 8 ,
.Xr installboot 8 ,
.Xr x86/boot 8
.Rs
.%T Preboot Execution Environment (PXE) Specification
.%N Version 2.1
.%D September 20, 1999
.%A Intel Corporation
.Re
.Sh HISTORY
The
.Nx Ns Tn /x86
.Nm
command first appeared in
.Nx 1.6 .
.Sh BUGS
If an error is encountered while reading the
.Nx
kernel file or if its file format wasn't recognized, it is
impossible to retry the operation because the
.Tn PXE
network stack is already removed from the system RAM.
.Pp
You need the
.Nm
from an i386 build to boot an i386 kernel,
and that from an amd64 build to boot an amd64 kernel.
.Pp
In a
.Tn Xen
setup, the
.Nx
DOM0 kernel is loaded as a module, and cannot know the device
from which the
.Tn Xen
hypervisor was booted.
In this case, the DOM0 kernel will fall back to the default boot
device (typically the first disk on the host).
If the boot device is different from the default one, consider
passing additional arguments, like
.Ar bootdev ,
to the DOM0 kernel as explained
in the
.Cm load
command subsection in
.Xr x86/boot 8 .