FreeBSD as read-only firmware
yerenkow at gmail.com
Sat Nov 3 16:08:58 UTC 2012
Actually in my case, base system image r24243.vmdk, have exactly two
partitions (gpt's freebsd-boot, and roots = freebsd-ufs), and second one is
used only in read-only :)
For virtual machines approach, base image can be even ISO, which will be
implied RO for system, and upgrade is just switch ISO.
For real hardware, it can be done with such approach - make two partitions
with fixed size, and when you need upgrade - just `dd` new image to other
partition, mark it as [bootonce] (And if all is ok, as [bootme]), reboot =
and you have new OS very quick, with same configs (except for some LARGE
changes which could happen in /etc and touch your configs), and with same
BTW, when you mount /etc-rw union over /etc, when you'll need upgrade,
mergemaster could take less time, less places for errors - since you had to
merge only changed files(which present on /etc-rw).
I think these days with current hw, no one will complain against lost 1Gb
to achieve clean and simple OS upgrade.
I'm not saying about possible way to shrink it further (no debug, gzip,
etc) - get lesser partition, but still RO, and get ability to make
something dd if=/dev/gpt/rootfs bs=1M | sha256
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