How to recover from setting boot_single=""?

[David Kurtz]

Short story: I placed a single line,

boot_single=""

into the previously empty file /boot/loader.conf and now my machine boots with an extremely limited read-only volume.

How do I get my old boot behavior back?


Long story: I was muddling through updating the kernel and world for the first time, going from FreeBSD 5.1 => 5.2. Following instructions in /usr/src/UPDATING I made backups, made buildworld, etc. until it got to the point where it says reboot in single user.

Never having done that, I tried first by "reboot"ing, but for some reason my USB keyboard doesn't get power until further on in the boot cycle, so I couldn't just "press 4." I looked through the docs and found instruction saying that I should set boot_single. I'm guessing I should have set it to something other than "", which is just copied from /boot/defaults/loader.conf.

So, a couple more questions: what is this limited read-only mode exactly? Where are my files (e.g. /usr is empty)? What should I have done? Is it possible to back out?

It's a personal sandbox, and everything I need is already safely backed up; if I need to just blast the whole system with a CD install, I can do that. But I am curious to know if it's possible to u-turn in this cul-de-sac. Apparently, I know just enough to get myself into trouble, but not enough to get out.