Message-ID: <68057416@news.ausics.net> From: not@telling.you.invalid (Computer Nerd Kev) Subject: Re: Shutdown - 25 Years Later Newsgroups: comp.os.linux.misc References: User-Agent: tin/2.0.1-20111224 ("Achenvoir") (UNIX) (Linux/2.4.31 (i586)) NNTP-Posting-Host: news.ausics.net Date: 21 Apr 2025 08:24:22 +1000 Organization: Ausics - https://newsgroups.ausics.net Lines: 31 X-Complaints: abuse@ausics.net Path: ...!weretis.net!feeder9.news.weretis.net!news.bbs.nz!news.ausics.net!not-for-mail Bytes: 2185 Pancho wrote: > If they can do it for shutdown, presumably this is some method, > some acknowledgement? On shutdown the filesystems are remounted read-only, shown here in dmesg (captured from serial port): EXT4-fs (sda3): re-mounted f109ff12-da03-4dfd-ad2a-cbd4eb713c43 ro. Quota mode: disabled. sd 0:0:0:0: [sda] Synchronizing SCSI cache reboot: Power off not available: System halted instead "mount -o ro /deb/sda3" should do the first part during normal operation too, but you'd need to have "/" on a ramdisk or tmpfs if every physical filesystem is being mounted read-only. I'm not so sure about "Synchronizing SCSI cache", is that like running sync or something else (it didn't appear in dmesg when I ran "sync" now)? A web search points to the "sg_sync" command from sg3_utils as a way of triggering it manually: https://manpages.debian.org/bookworm/sg3-utils/sg_sync.8.en.html It sounds like they're talking about the cache in the drive itself, making sure data is physically written out before power-off. Sounds like a good idea. I wonder if there's a risk to unplugging unmounted USB HDDs without doing that? Or does it only have a real effect on actual SCSI drives (none present on the system where that kernel message was captured)? -- __ __ #_ < |\| |< _#