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To be safe, once the test machine is in the proper configuration, make a backup
copy of the root filesystem.
Booting an Alternate Kernel
A kernel other than /platform/*/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. By default, the first
module directory in the module directory path is the one the kernel resides in.
By booting kernel.orig/unix, the module directory path becomes
/platform/sun4c/kernel.orig /kernel /usr/kernel.
Note – 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 5.5 Version Generic [UNIX(R) System V Release 4.0]
Copyright (c) 1983-1995, Sun Microsystems, Inc.
...
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Writing Device Drivers—May 1996