It seems in a hard crash, in particular failure of a UPS to keep a system running, that some of the contents of logs get lost due to file system caching. As an experiment, I tried mounting the /var partition with the sync option. There was substantially more disk noise on a boot up, but the show stopper was trying to run apt. The disk pounded away while apt sat there unresponsive.
Is it a mistake to mount /var sync, or is one of the options such as relatime, strictatime or noatime required for success? If so, is it safe to use one of these options on /var?