sysupgrade is a utility to upgrade OpenBSD to the next release or
a new snapshot if available.
sysupgrade downloads the necessary files to /home/_sysupgrade,
verifies them with signify(1), and copies bsd.rd to /bsd.upgrade.
sysupgrade by default then reboots the system. The bootloader will
automatically choose /bsd.upgrade, triggering a one-shot upgrade
using the files in /home/_sysupgrade.