Typically do single branch clones of /usr/src so that it doesnt take up too much space:
git clone <url> --branch <branch> --single-branch /usr/src
Move to a new branch/release
git remote set-branches --add upstream releng/12.1
git fetch upstream releng/12.1
git checkout releng/12.1
Build FreeBSD:
make buildworld && make buildkernel && make installkernel && make installworld
Post upgrade make sure to run mergemaster:
mergemaster -Ui
Update pkgng:
pkg-static install -f pkg
pkg update
pkg upgrade
Set dumpdev=AUTO in its /etc/rc.conf, and have sufficiently large swap partition, configured at boot time.
On FreeBSD, a kernel core file can be generated by intentionally crashing:
# sysctl debug.kdb.panic=1
For machines that are configured to enter the on-line kernel debugger (aka kdb), the following command is also needed, at the system console during a panic:
kdb> call doadump
Otherwise, the kernels dump routines will automatically save the core file to a swap partition, if configured.
Upon reboot, the savecore rc startup script will automatically identify the core file in the swap partition, and save it to /var/crash by default.