Most of the OpenBSD systems I am in charge of are deployed in data centres, powered by UPSs which provide them with electrical power during periods of public grid power outages. But there is also a number of OpenBSD systems I administer, which are deployed in much less favourable conditions; where frequent power outages last longer than UPS batteries do, or where there are no UPSs at all (such as branch office routers in godforsaken places where having electricity and Internet access at all is considered a lucky circumstance). These latter systems are likely to have high rate of unclean shutdowns caused by prolonged or unexpected power outages, which in turn increase the probability of their inability to boot without human intervention. This article describes steps to make OpenBSD system more resilient to unexpected power outages by minimising the possibility of inconsistent file systems after unclean shutdowns, which is achieved by mounting all disk partitions in read-only mode. Filesystems which have to be writable -
/tmp - are mounted as writable memory file systems.