Re: nextboot warns it won't reset

> On Jul 19, 2024, at 10:19 AM, Warner Losh <imp@bsdimp.com> wrote:
> 
> 
> 
> On Thu, Jul 18, 2024, 7:10 PM Zhenlei Huang <zlei@freebsd.org <mailto:zlei@freebsd.org>> wrote:
> 
> 
>> On Jul 19, 2024, at 4:45 AM, Gareth de Vaux <stable@lordcow.org <mailto:stable@lordcow.org>> wrote:
>> 
>> Hi all, nextboot warns as follows:
>> 
>> # nextboot -k testkernel
>> WARNING: loader(8) has only R/O support for ZFS
>> nextboot.conf will NOT be reset in case of kernel boot failure
>> 
>> 
>> This's on a ZFS zroot 12.4-STABLE system.
> 
> You're encouraged to upgrade to supported releases ;)
> 
>> 
>> Does this mean that nextboot will not do its job?
> 
> I think the WARNING is a good hint and explain why it does not work incase boot failure.
> 
> The implementation of load desired kernel is write loader parameters to /boot/nexboot.conf , to indicate
> the loader(8) do its job, that is loading the desired kernel on next boot. Well it is a oneshot boot
> so the loader will try to disable these parameters by writing `nextboot_enable=NO` to  /boot/nexboot.conf.
> 
> That is the magic. Apparently if loader(8) does not support write to filesystem, in this case the ZFS, 
> it will fail to write /boot/nexboot.conf in case kernel boot failure. Thus subsequent boot the loader(8) would
> still try to boot from the oneshot `testkernel`.
> 
> However, ZFS has special support via properties in the BE that lets you do boot once and nextboot stuff.

Yes and NO.

Yes for 13.x, 14.x and CURRENT. nextboot(8) will consults zfsbootcfg(8) to do the nextboot stuff if file system
is ZFS.

No for 12.x.  neither nextboot(8) nor nextboot.sh will do that. And it seems that loader(8) also do not get / set
ZFS properties to enable / disable nextboot stuff.

> 
> But even better are boot environments. That's a more comple solution that supports bootnext features and more. See bectl...
> 
> Warner 
> 
>> I see a blog mentioning that nextboot will write metadata to the ZFS pool label,
>> in which case maybe the warning is no longer applicable?
> 
> That is implementation specific. Normally you can ignore the warning, unless you have trouble booting
> the kernel.
> 
>> 
>> 
>> Also I suspect I should rather run "nextboot -D" to revert the situation.
>> Is this equivalent to removing /boot/nextboot.conf and/or this metadata in the
>> ZFS pool label?
> 
> I think normally you do not need that.
> 
> Best regards,
> Zhenlei