OpenBSD has introduced a new utility in the most recent version (6.6 – now in -current). This is sysupgrade, which makes upgrading the system even more painless than it was previously.
sysupgradedownloads the necessary files to /home/_sysupgrade, verifies them with signify(1), and copies bsd.rd to /bsd.upgrade.
sysupgradeby default then reboots the system. The bootloader will automatically choose /bsd.upgrade, triggering a one-shot upgrade using the files in /home/_sysupgrade.
This is brilliant. I do upgrades to -current about once a week. Previously I had to reboot with a new bsd.rd and connect to a mirror to do the upgrade. Downloading the files took some time (more than 20 min) during which the computer was not available for work. Now I just run sysupgrade and everything happens automatical. I can continue to use the computer while the files are being downloaded, after which the system reboots with the new upgrade. This is a major advance in ease of use – congratulations to OpenBSD!
Incidentally it also works for upgrading -release versions; it knows whether you are using -release or -current.