Just out of curiousity, why don't you set the SR before you boot the machine?
That way it'll come up single user, and you can icheck/dcheck before you go
to multi-user mode. I prefer doing it that way, there's as little as possible
going on, in case the disk is slightly 'confused', so less chance any bit-rot
I actually do file system checks on v5 as it's the early unix I use the most:
check -l /dev/rk0
check -u /dev/rk0
same for rk1, rk2.
The v5 manual entry for check references the 'restor' command,
although the man page for that is missing.
Your idea of starting up in single user mode is a good one although
I'm not sure if it's necessary to check the file system on each boot
up. I've been running this disk image of v5 for about two years and no
blow-ups as yet. I also keep various snapshots of v5, v6 and v7 disk
images for safety reasons.
And there are text files of all the source code changes I've made, so
if disaster strikes I can redo it all.