471 lines
11 KiB
Groff
471 lines
11 KiB
Groff
.\" Copyright (c) 1994 Gordon W. Ross, Theo de Raadt
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.\" Updated by Luigi Rizzo, Robert Watson
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. The name of the author may not be used to endorse or promote products
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.\" derived from this software without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
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.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
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.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd January 10, 2004
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.Dt DISKLESS 8
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.Os
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.Sh NAME
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.Nm diskless
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.Nd booting a system over the network
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.Sh DESCRIPTION
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The ability to boot a machine over the network is useful for
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.Em diskless
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or
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.Em dataless
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machines, or as a temporary measure while repairing or
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re-installing file systems on a local disk.
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This file provides a general description of the interactions between
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a client and its server when a client is booting over the network.
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.Sh OPERATION
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When booting a system over the network, there are three
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phases of interaction between client and server:
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.Bl -enum
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.It
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The stage-1 bootstrap, typically PXE built into your Ethernet
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card, loads a second-stage boot program.
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.It
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The second-stage boot program, typically
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.Xr pxeboot 8 ,
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loads modules and
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the kernel, and boots the kernel.
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.It
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The kernel
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.Tn NFS
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mounts the root directory and continues from there.
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.El
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.Pp
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Each of these phases are described in further detail below.
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.Pp
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First, the stage-1 bootstrap loads the stage-2 boot program over
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the network.
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The stage-1 bootstrap typically uses
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.Tn BOOTP
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or
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.Tn DHCP
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to obtain the filename to load, then uses
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.Tn TFTP
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to load the file.
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This file is typically called
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.Pa pxeboot ,
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and should be copied from
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.Pa /boot/pxeboot
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into the
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.Tn TFTP
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directory on the server, which is typically
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.Pa /tftpdir .
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.Pp
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The stage-2 boot program then loads additional modules and the kernel.
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These files may not exist on the
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.Tn DHCP
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or
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.Tn BOOTP
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server.
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You can use the
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.Ic next-server
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option available in
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.Tn DHCP
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configurations to specify the server holding
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the second stage boot files and kernel.
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The stage-2 program uses
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.Tn NFS
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or
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.Tn TFTP
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to obtain these files.
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By default,
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.Tn NFS
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is used.
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If you are using
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.Xr pxeboot 8 ,
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you can install a version that uses
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.Tn TFTP
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by setting
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.Li LOADER_TFTP_SUPPORT=YES
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in your
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.Pa /etc/make.conf ,
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then recompiling and reinstalling
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.Xr pxeboot 8
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via the command listed below.
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It is often necessary to use
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.Tn TFTP
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here so you can place a custom kernel
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in
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.Pa /tftpdir/ .
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If you use
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.Tn NFS
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and do not have a custom root file system for the
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.Nm
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client, the stage-2 boot will load your server's kernel as the kernel for
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the
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.Nm
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machine, which may not be what you want to have happen.
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.Bd -literal -offset indent
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cd /usr/src/sys/boot/i386
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make clean; make; make install
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cp /boot/pxeboot /tftpdir/
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.Ed
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.Pp
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In phase 3, the kernel acquires IP networking configuration in one
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of two ways, and then proceeds to mount the root file system and start
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operation.
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If the phase 2 loader supports passing network configuration to the
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kernel using the kernel environment, then the kernel will configure
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the network interface using that information.
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Otherwise, it must use
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.Tn DHCP
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or
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.Tn BOOTP
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to acquire
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configuration information.
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The boot
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scripts recognize a
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.Nm
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startup and perform
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the actions found in
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.Pa /etc/rc.d/initdiskless
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and
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.Pa /etc/rc.d/diskless .
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On older systems, the scripts are located in
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.Pa /etc/rc.diskless1
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and
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.Pa /etc/rc.diskless2 .
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.Sh CONFIGURATION
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In order to run a
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.Nm
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client, you need the following:
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.Bl -bullet
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.It
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An
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.Tn NFS
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server which exports a root and
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.Pa /usr
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partitions with appropriate permissions.
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The
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.Nm
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scripts work with read-only partitions, as long as root is exported with
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.Fl maproot Ns =0
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so that some system files can be accessed.
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As an example,
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.Pa /etc/exports
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can contain the following lines:
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.Bd -literal -offset indent
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<ROOT> -ro -maproot=0 -alldirs <list of diskless clients>
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/usr -ro -alldirs <list of diskless clients>
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.Ed
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.Pp
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where
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.Aq ROOT
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is the mount point on the server of the root partition.
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The script
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.Pa /usr/share/examples/diskless/clone_root
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can be used to create a shared read-only root partition,
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but in many cases you may decide to export
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(again as read-only) the root directory used by
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the server itself.
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.It
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A
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.Tn BOOTP
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or
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.Tn DHCP
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server.
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.Xr bootpd 8
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can be enabled by
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uncommenting the
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.Dq Li bootps
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line in
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.Pa /etc/inetd.conf .
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A sample
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.Pa /etc/bootptab
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can be the following:
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.Bd -literal -offset indent
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.default:\\
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hn:ht=1:vm=rfc1048:\\
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:sm=255.255.255.0:\\
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:sa=<SERVER>:\\
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:gw=<GATEWAY>:\\
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:rp="<SERVER>:<ROOT>":
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<CLIENT>:ha=0123456789ab:tc=.default
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.Ed
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.Pp
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where
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.Aq SERVER ,
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.Aq GATEWAY
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and
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.Aq ROOT
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have the obvious meanings.
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.It
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A properly initialized root partition.
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The script
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.Pa /usr/share/examples/diskless/clone_root
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can help in creating it, using the server's root partition
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as a reference.
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If you are just starting out, you should
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simply use the server's own root directory,
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.Pa / ,
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and not try to clone it.
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.Pp
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You often do not want to use the same
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.Pa rc.conf
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or
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.Pa rc.local
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files for the
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.Nm
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boot as you do on the server.
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The
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.Nm
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boot
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scripts provide a mechanism through which you can override various files
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in
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.Pa /etc
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(as well as other subdirectories of root).
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The scripts provide four
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overriding directories situated in
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.Pa /conf/base ,
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.Pa /conf/default ,
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.Pa /conf/<broadcast-ip> ,
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and
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.Pa /conf/<machine-ip> .
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You should always create
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.Pa /conf/base/etc ,
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which will entirely replace the server's
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.Pa /etc
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on the
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.Nm
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machine.
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You can clone the server's
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.Pa /etc
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here or you can create a special file which tells the
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.Nm
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boot scripts
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to remount the server's
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.Pa /etc
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onto
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.Pa /conf/base/etc .
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You do this by creating the file
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.Pa /conf/base/etc/diskless_remount
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containing the mount point to use as a basis of the
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.Nm
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machine's
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.Pa /etc .
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For example, the file might contain:
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.Pp
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.Dl 10.0.0.1:/etc
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.Pp
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Alternatively, if the server contains several independent roots, the file
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might contain:
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.Pp
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.Dl 10.0.0.1:/usr/diskless/4.7-RELEASE/etc
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.Pp
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This would work, but if you copied
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.Pa /usr/diskless/4.7-RELEASE
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to
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.Pa /usr/diskless/4.8-RELEASE
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and upgraded the installation, you would need to modify the
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.Pa diskless_remount
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files to reflect that move.
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To avoid that, paths in
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.Pa diskless_remount
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files beginning with
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.Pa /
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have the actual path of the client's root prepended to them so the file
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could instead contain:
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.Pp
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.Dl /etc
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.Pp
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The
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.Nm
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scripts create memory file systems to hold the overridden
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directories.
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Only a 2MB partition is created by default, which may not
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be sufficient for your purposes.
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To override this, you can create the
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file
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.Pa /conf/base/etc/md_size
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containing the size, in 512 byte sectors, of the memory disk to create
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for that directory.
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.Pp
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You then typically provide file-by-file overrides in the
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.Pa /conf/default/etc
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directory.
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At a minimum, you must provide overrides for
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.Pa /etc/fstab , /etc/rc.conf ,
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and
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.Pa /etc/rc.local
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via
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.Pa /conf/default/etc/fstab , /conf/default/etc/rc.conf ,
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and
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.Pa /conf/default/etc/rc.local .
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.Pp
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Overrides are hierarchical.
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You can supply network-specific defaults
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in the
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.Pa /conf/ Ns Ao Ar BROADCASTIP Ac Ns Pa /etc
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directory, where
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.Aq Ar BROADCASTIP
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represents the broadcast IP address of
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the
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.Nm
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system as given to it via
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.Tn BOOTP .
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The
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.Pa diskless_remount
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and
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.Pa md_size
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features work in any of these directories.
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The configuration feature works on directories other then
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.Pa /etc ,
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you simply create the directory you wish to replace or override in
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.Pa /conf/{base,default,<broadcast>,<ip>}/*
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and work it in the same way that you work
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.Pa /etc .
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.Pp
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Since you normally clone the server's
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.Pa /etc
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using the
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.Pa /conf/base/etc/diskless_remount ,
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you might wish to remove unneeded files from the memory file system.
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For example,
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if the server has a firewall but you do not, you might wish
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to remove
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.Pa /etc/ipfw.conf .
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You can do this by creating a
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.Pa /conf/base/ Ns Ao Ar DIRECTORY Ac Ns Pa .remove
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file.
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For example,
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.Pa /conf/base/etc.remove ,
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which contains a list of relative paths that the boot scripts should remove
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from the memory file systems.
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.Pp
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As a minimum, you normally need to have the following in
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.Pa /conf/default/etc/fstab
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.Bd -literal -offset indent
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<SERVER>:<ROOT> / nfs ro 0 0
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<SERVER>:/usr /usr nfs ro 0 0
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proc /proc procfs rw 0 0
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.Ed
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.Pp
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You also need to create a customized version of
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.Pa /conf/default/etc/rc.conf
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which should contain
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the startup options for the
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.Nm
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client, and
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.Pa /conf/default/etc/rc.local
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which could be empty but prevents the server's own
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.Pa /etc/rc.local
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from leaking onto the
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.Nm
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system.
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.Pp
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In
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.Pa rc.conf ,
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most likely
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you will not need to set
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.Va hostname
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and
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.Va ifconfig_*
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because these will be already set by the startup code.
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Finally, it might be convenient to use a
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.Ic case
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statement using
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.Li `hostname`
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as the switch variable to do machine-specific configuration
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in case a number of
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.Nm
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clients share the same configuration
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files.
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.It
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The kernel for the
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.Nm
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clients, which will be loaded using
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.Tn NFS
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or
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.Tn TFTP ,
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must include support for the NFS client:
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.Pp
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.D1 Cd "options NFSCLIENT"
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.D1 Cd "options NFS_ROOT"
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.Pp
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If you are using a boot mechanism that does not pass network configuration
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to the kernel using the kernel environment, you will also need to include
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the following options:
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.Pp
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.D1 Cd "options BOOTP"
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.D1 Cd "options BOOTP_NFSROOT"
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.D1 Cd "options BOOTP_COMPAT"
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.Pp
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.Em Note :
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the PXE environment does not require these options.
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.Pp
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The
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.Nm
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booting environment relies on memory-backed file systems to
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support temporary local storage in the event that the root file system
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is mounted read-only; as such, it is necessary to add the following
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to the device section of the kernel configuration:
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.Pp
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.D1 Cd "device md"
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.Pp
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If you use the firewall, remember to default to
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.Dq open ,
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or your kernel
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will not be able to send/receive the
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.Tn BOOTP
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packets.
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.El
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.Sh SECURITY ISSUES
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Be warned that using unencrypted
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.Tn NFS
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to mount root and user
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partitions may expose information such as
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encryption keys.
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.Sh BUGS
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This manpage is probably incomplete.
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.Pp
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.Fx
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sometimes requires to write onto
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the root partition, so the startup scripts mount MFS
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file systems on some locations (e.g.\&
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.Pa /etc
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and
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.Pa /var ) ,
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while
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trying to preserve the original content.
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The process might not handle all cases.
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.Sh SEE ALSO
|
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.Xr ethers 5 ,
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.Xr exports 5 ,
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.Xr bootpd 8 ,
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.Xr mountd 8 ,
|
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.Xr nfsd 8 ,
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.Xr pxeboot 8 ,
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.Xr reboot 8 ,
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.Xr tftpd 8
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.Pp
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.Pa ports/net/etherboot
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