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diskless - booting a system over the network
Each of these phases are described in further detail below.
First, the stage-1 bootstrap loads the stage-2 boot program over the network. The stage-1 bootstrap typically uses BOOTP or DHCP to obtain the filename to load, then uses TFTP to load the file. This file is typically called pxeboot and should be copied from /boot/pxeboot into the TFTP directory on the server, which is typically /tftpdir
The stage-2 boot program then loads additional modules and the kernel. These files may not exist on the DHCP or BOOTP server. You can use the next-server option available in DHCP configurations to specify the server holding the second stage boot files and kernel. The stage-2 program uses NFS or TFTP to obtain these files. By default, NFS is used. If you are using pxeboot(8), you can install a version that uses TFTP by setting LOADER_TFTP_SUPPORT=YES in your make.conf5, then recompiling and reinstalling pxeboot(8) via the command listed below. It is often necessary to use TFTP here so you can place a custom kernel in /tftpdir/ If you use NFS and do not have a custom root file system for the client, the stage-2 boot will load your server's kernel as the kernel for the machine, which may not be what you want to have happen.
cd /usr/src/sys/boot/i386 make clean; make; make install cp /boot/pxeboot /tftpdir/
In phase 3, the kernel acquires IP networking configuration in one of two ways, and then proceeds to mount the root file system and start operation. If the phase 2 loader supports passing network configuration to the kernel using the kernel environment, then the kernel will configure the network interface using that information. Otherwise, it must use DHCP or BOOTP to acquire configuration information. The boot scripts recognize a startup and perform the actions found in /etc/rc.d/resolv /etc/rc.d/tmp /etc/rc.d/var and /etc/rc.initdiskless
<ROOT> -ro -maproot=0 -alldirs <list of diskless clients> /usr -ro -alldirs <list of diskless clients>
where Aq ROOT is the mount point on the server of the root partition. The script /usr/share/examples/diskless/clone_root can be used to create a shared read-only root partition, but in many cases you may decide to export (again as read-only) the root directory used by the server itself.
.default:\
hn:ht=1:vm=rfc1048:\
:sm=255.255.255.0:\
:sa=<SERVER>:\
:gw=<GATEWAY>:\
:rp="<SERVER>:<ROOT>":
<CLIENT>:ha=0123456789ab:tc=.default
where Aq SERVER , Aq GATEWAY and Aq ROOT have the obvious meanings.
You often do not want to use the same rc.conf or rc.local files for the boot as you do on the server. The boot scripts provide a mechanism through which you can override various files in /etc (as well as other subdirectories of root).
One difference that you should pay particular attention to is the value of local_startup in /etc/defaults/rc.conf A typical value for a boot is mountcritremote however your needs may be different.
The scripts provide four overriding directories situated in /conf/base /conf/default /conf/<broadcast-ip> and /conf/<machine-ip> You should always create /conf/base/etc which will entirely replace the server's /etc on the machine. You can clone the server's /etc here or you can create a special file which tells the boot scripts to remount the server's /etc onto /conf/base/etc You do this by creating the file /conf/base/etc/diskless_remount containing the mount point to use as a basis of the machine's /etc For example, the file might contain:
10.0.0.1:/etc
Alternatively, if the server contains several independent roots, the file might contain:
10.0.0.1:/usr/diskless/4.7-RELEASE/etc
This would work, but if you copied /usr/diskless/4.7-RELEASE to /usr/diskless/4.8-RELEASE and upgraded the installation, you would need to modify the diskless_remount files to reflect that move. To avoid that, paths in diskless_remount files beginning with / have the actual path of the client's root prepended to them so the file could instead contain:
/etc
The scripts create memory file systems to hold the overridden directories. Only a 2MB partition is created by default, which may not be sufficient for your purposes. To override this, you can create the file /conf/base/etc/md_size containing the size, in 512 byte sectors, of the memory disk to create for that directory.
You then typically provide file-by-file overrides in the /conf/default/etc directory. At a minimum, you must provide overrides for /etc/fstab , /etc/rc.conf and /etc/rc.local via /conf/default/etc/fstab , /conf/default/etc/rc.conf and /conf/default/etc/rc.local
Overrides are hierarchical. You can supply network-specific defaults in the /conf/ Ao BROADCASTIP Ac /etc directory, where Aq Ar BROADCASTIP represents the broadcast IP address of the system as given to it via BOOTP The diskless_remount and md_size features work in any of these directories. The configuration feature works on directories other then /etc you simply create the directory you wish to replace or override in /conf/{base,default,<broadcast>,<ip>}/* and work it in the same way that you work /etc
Since you normally clone the server's /etc using the /conf/base/etc/diskless_remount you might wish to remove unneeded files from the memory file system. For example, if the server has a firewall but you do not, you might wish to remove /etc/ipfw.conf You can do this by creating a /conf/base/ Ao DIRECTORY Ac .remove file. For example, /conf/base/etc.remove which contains a list of relative paths that the boot scripts should remove from the memory file systems.
As a minimum, you normally need to have the following in /conf/default/etc/fstab
<SERVER>:<ROOT> / nfs ro 0 0 <SERVER>:/usr /usr nfs ro 0 0 proc /proc procfs rw 0 0
You also need to create a customized version of /conf/default/etc/rc.conf which should contain the startup options for the client, and /conf/default/etc/rc.local which could be empty but prevents the server's own /etc/rc.local from leaking onto the system.
In rc.conf most likely you will not need to set hostname and ifconfig_* because these will be already set by the startup code. Finally, it might be convenient to use a case statement using `hostname` as the switch variable to do machine-specific configuration in case a number of clients share the same configuration files.
If you are using a boot mechanism that does not pass network configuration to the kernel using the kernel environment, you will also need to include the following options:
Note the PXE environment does not require these options.
The booting environment relies on memory-backed file systems to support temporary local storage in the event that the root file system is mounted read-only; as such, it is necessary to add the following to the device section of the kernel configuration:
If you use the firewall, remember to default to ``open'' or your kernel will not be able to send/receive the BOOTP packets.
Fx sometimes requires to write onto the root partition, so the startup scripts mount MFS file systems on some locations (e.g. /etc and /var ) while trying to preserve the original content. The process might not handle all cases.
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