Normally, the
b command alone is sufficient to boot the system, as the PROM chooses a default boot device
dev if none is specified. The PROM chooses the first device present on the system from the following ordered list:
sd SCSI disk
ie Intel Ethernet
ec 3Com Ethernet
Unless specified, the controller number
cntrl, unit number
unit, and partition number
part default to zero, which is almost always correct.
The controller number can be specified if there is more than one of the given device in the system. For example, use “ie(1,,)” to boot off of the second Intel Ethernet in the system.
The unit number specifies one of the many devices attached to a controller. The exact meaning and values vary depending on the device name. For example, “sd(,18,)” boots the disk at target 6 on the first SCSI controller, 18 being the target number 6, multiplied by 4, and given in hexadecimal.
The partition number specifies one of the many partitions on a device. The exact meaning and values vary depending on the device name. For example, “sd(,18,1)” boots the second partition on the disk at target 6 on the first SCSI controller.
The PROM only loads a first-stage boot program, currently either
/usr/mdec/bootxx (for a disk boot), or
/usr/mdec/bootyy (for a network boot). This first-stage boot program then loads the second-stage boot program from the same device, currently either
/usr/mdec/ufsboot (for a disk boot), or
/usr/mdec/netboot (for a network boot).
The second-stage boot program will then attempt to load the kernel named
file (or
vmunix if none is specified). The second-stage disk boot program
/usr/mdec/ufsboot loads the kernel from the same device that it was loaded from, while the second-stage network boot program
/usr/mdec/netboot will load the kernel from the NFS root as determined by the procedure described in
diskless(8).