It appears to be the case that if a fresh install, e.g. of 12.0-RELEASE onto a hard drive which has previously had all of its partitions removed (but not its partition table), e.g. under Ubuntu/Linux, via the gparted tool, may result in a system that will not boot. This specifically happened to me when I attemtped to do a fresh install of 12.0-RELEASE onto such a hard drive. Note that in this specific case I had elected to perform "manual" partitioning during the FreeBSD install process. I ended up resolving this problem by putting the drive, temporarily, into an existing FreeBSD system and then doing the following steps: 1) gpart destroy -F ada0 2) dd if=/dev/zero of=/dev/ada0 bs=1M count=10 3) Re-doing the entire FreeBSD install from scratch The fact that these steps resulted in a bootable FreeBSD system suggests to me that there are some things that aren't being done properly, i.e. to clear out old partition-related cruft, when and if one is doing a fresh install of FreeBSD, but possibly only when the person doing the install has elected to perform manual partitioning during the install process, and possibly only when all old partitions (but not the partition table) have been removed previously using, e.g., Linux+gparted.
I do believe that you are correct in that this is only triggered by a manual partitioning operation. The other types of installs do in fact wipe out and write an new partition table. Can you go into some detail about what you did during the manual partition operations? I have had a couple experiences here, and I know from first hand experience that if you do not produce a valid setup things go very wrong in spectacular ways.
I can only tell you what I *believe* I did, obviously, since I wasn't videoing myself as I did this. (Maybe I will next time! :-) I'm not sure that any of this info will help though, as I believe that I did all of the exact same manual partitioning actions the second time around, i.e. *after* I had *also* done: 1) gpart destroy -F ada0 2) dd if=/dev/zero of=/dev/ada0 bs=1M count=10 However on this second install attempt everything worked, no problem. Anyway, what I did, to the best of my recollection was this: I started out, of course, selecting GPT as the partitioning scheme. I created a 1 GiB / (root) partition... type freebsd-ufs of course. I created a 16 GiB swap partition (freebsd-swap). The rest is as you can see here, which is the "df -k" output from my (now running) system: /dev/ada0p2 1014940 231756 701992 25% / devfs 1 1 0 100% /dev /dev/ada0p4 3044988 1174092 1627300 42% /var /dev/ada0p5 2031132 16444 1852200 1% /var/ftp /dev/ada0p6 1015324 392428 541672 42% /tmp /dev/ada0p7 16233660 8574620 6360348 57% /usr /dev/ada0p8 32487548 22888624 6999924 77% /home /dev/ada0p9 400156276 258842812 109300964 70% /v /dev/ada0p10 473796804 32808 435860252 0% /w procfs 4 4 0 100% /proc I hope and trust that this answers your question.