Re: [TUHS] was turmoil, moving to rm -rf /

I once had to rebuild the root directory using ROM based disk IO and memory peek and poke commands! At this late date I don’t recall many details but at least the root block was trashed during some last minute testing. Unlikely it was “rm -rf / something” as that would’ve done far more damage. The situation was this: 1. We had *one* working hardware system[1]. 2. At that time we only had working floppy controller and driver[2]. 3. Our devel system was a VAX running 4.1BSD. no support for the floppy drive so everything had to be downloaded over a 9600 serial link. 4. The backup floppy either didn’t exist or wasn’t readable. 5. We had custom stuff that was done for a show and not backed up anywhere. Luckily, due to earlier debugging sessions I knew what the file system layout was — this was on a version 7 system, with 16 byte dir entries, 2 bytes inode #, followed by and 14 byte name. IIRC inode 0 was not used, inode 1 was used as a temp during fsck based recovery and inode 2 was for the real root. So I read in the root inode, found the disk address of its data block, read it in, using fixed up “.” and “..” and “/bin” entries — usually inode #3 was bin, wrote it back to the floppy and rebooted. I think the unix image was in /bin. On reboot fsck worked and reconnected all the lost directories, which were easy to figure out and rename. The back story is that this happened on a Saturday just before the Fall Comdex 1981, where we were going to show our system for the first time and we had to take a working system to Las Vegas by Sunday[3]. We were able to fly out on time and the Comdex show was a success, with thousands of leads generated. In terms of lessons, I don’t know what we learned. I guess it pays to be intimately familiar with the system as we were in an extreme bootstrap situation with very little working reliably. Seems often startups end up doing acrobatics without a net! — bakul [1] Two actually, but the second was a wire wrapped prototype. This was at an early Unix workstation startup; our main app was “word processing”. [2] Later we hooked up a Western Digital ST506 controller via parallel port and I was very happy when my disk driver could do 25 KB/s! No DMA so had to do programmed IO. [3] Rob Warnock (whom some of you may know from his SGI days) was our very hands-on CTO, and he was/is great at debugging/problem solving. I don’t know why they waited for me rather than call Rob. a) I was a junior engineer as that my first job with C & Unix (6 months at that time) and b) I had already worked about 80+ hours that week and gone home to sleep at 9AM on Saturday. May be Rob was smart enough to not answer his phone!