I might be missing something, but the order I know and have always seen recommended is REISUB. Terminating processes might write data to disk, so it seems to me like you should sync after, not before. Though this is also generally unimportant with modern filesystems and storage media.
I recommend starting with SysRq+E before that, there’s a chance it gets whatever the shutdown was waiting for. And if that fails… REISUB my beloved.
RSEIUB. Raising skinny elephants is utterly boring.
I might be missing something, but the order I know and have always seen recommended is REISUB. Terminating processes might write data to disk, so it seems to me like you should sync after, not before. Though this is also generally unimportant with modern filesystems and storage media.