Is there any way to tell the boot script to use the "-y" flag in fsck?
If something goes wrong with simple fsck, I always simply do a "fsck
-y". There is no other option for me. So, it would be VERY useful if
this could be done automatically instead of interrupting the router startup.
Thanks.
On 6/5/19 1:30 AM, Nick Holland wrote:
On 6/4/19 1:29 PM, Mogens Jensen wrote:
I'm going to build a router for use in a remote location, and I have
chosen OpenBSD 6.5 for the task. Unfortunately, it's not possible to
protect the router with an UPS, so it will have to be resilient enough
to survive sudden power outages and still boot without manual
intervention.
In the past I have built a few Linux based routers and they were
configured to run from RAM. I have made some research to see if this is
also possible on OpenBSD and found that, while there are solutions to
have / read-only, none of this is officially supported.
Can anyone with experience running OpenBSD routers without UPS, tell if
filesystem corruption is going to be a problem after power outages, or
if there are any officially supported ways to make the system resilient
enough to not break after a power outage?
I'm using an mSATA disk with MLC flash in the router.
I realized a few decades ago that consumer UPSs are a bad investment.
Industrial UPSs are a dubious idea in business unless you have a
dual-power supply machine and can hook each PS to a DIFFERENT UPS -- in
my area, grid power is more reliable than cheap UPSes (your mileage may
vary). And you have to MAINTAIN your UPSs, otherwise after a few years,
UPSs turn minor glitches into power outages (thank you very much).
I'm also fond of proving my own claims, so I very often just yank the
cord on my systems rather than doing orderly shutdowns.
Yes, if you drop power on an OpenBSD system, you will get an fsck on
reboot. Solution: Make your partitions as small as reasonable. Just
because you got a 500G disk for cheap, no reason to allocate all 500G.
For a router, 10G is PLENTY, and will fsck quickly. If you have slow
media (i.e., flash drives), you might want to aim for 1G. Every once in
a long while, you might catch a really bad time for the power to go out,
and have to manually say "Fix it!" to fsck, but for the most part, the
system will just come back up after the power comes back on.
The less you write to disk, the less risk you have of having to manually
intervene in your system's reboot. IF you want to do some fancy
logging, keep the logging partition out of the fstab file, and have a
script that brings it up with a "fsck -y" AFTER the system comes up, and
start the fancy logging AFTER the big logging partition successfully mounts.
But don't do stupid games to try to improve your chances, just make sure
there's a monitor and keyboard available to fix any problems that might
happen. Simple systems have simple problems. Complex systems break in
complex ways. You want me to swear you'll never have to manually
intervene in boot after an "event"? Nope. But I've walked
non-technical people through single-user fsck's over the phone; when
your bastardized system breaks, you will be down for a lot longer and
you will be going on-site to fix.
Nick.
