Booting an Alternate Kernel

A kernel other than /platform/`uname -i`/kernel/unix can be booted by specifying it as the boot file. In fact, backup copies of all the system drivers in /platform/* can be made and used if the original drivers fail (this is probably more useful if more than one driver is being debugged). For example:

# cp -r /platform/sun4c/kernel /platform/sun4c/kernel.orig

To boot the original system, boot kernel.orig/unix.

During testing, the new driver should be placed in /platform/sun4c/kernel (and not in /kernel or /usr/kernel) so that, the driver is not loaded if the system is booted out of kernel.orig. Alternatively, the module path can be changed by booting with the ask (-a) option.

ok boot kernel.orig/unix
...

Rebooting with command: kernel.orig/unix
Boot device: /sbus/esp@0,800000/sd@1,0   File and args:kernel.orig/unix
SunOS Release 5.7 Version Generic [UNIX(R) System V Release 4.0]
Copyright (c) 1983-1998, Sun Microsystems, Inc.
...

For more complete control, boot with the ask (-a) option; this allows alternate boot parameters to be specified (such as /dev/null or /etc/system.orig if that is the saved original system file that was copied earlier).

ok boot -a
...

Rebooting with command: disk1 -a
Boot device: /sbus/esp@0,800000/sd@1,0   File and args: -a
Enter filename [/kernel/unix]: kernel.orig/unixEnter default directory for modules
[/platform/SUNW,Sun_4_75/kernel.orig /kernel /usr/kernel]:<CR>SunOS Release 5.7 Version Generic [UNIX(R) System V Release 4.0]
Copyright (c) 1983-1998, Sun Microsystems, Inc.
Name of system file [etc/system]: etc/system.origroot filesystem type [ufs]: <CR>Enter physical name of root device
[/sbus@1,f8000000/esp@0,800000/sd@1,0:a]: <CR>