[SOLVED] Re: labelling root file system (RELENG_8)

[Andriy Gapon]

on 08/06/2011 19:55 Jeremy Chadwick said the following:
> On Wed, Jun 08, 2011 at 07:40:03PM +0300, Andriy Gapon wrote:
>> on 08/06/2011 19:26 Jeremy Chadwick said the following:
>>> I have the exact same question except not with regards to labels but
>>> toggling TRIM capability on the root filesystem.
>>>
>>> - Start system
>>> - At loader, boot single-user (option 4)
>>> - At prompt choose /bin/sh
>>> - mount -a
>>
>> I think that this is a culprit.
> 
> I'll try removing this step.
> 
>>> - tunefs -t enable /dev/ada0s1a --- fails
>>
>> Shouldn't you have / mounted r/o here?
>> BTW, AFAIR, *re*-mounting root read-only won't help; it needs to have never been
>> mounted r/w.
> 
> I'm a little confused by this sentence, so my apologise in advance.  /
> is mounted read-only in single-user by default.  Did you mean I should
> make it r/w by doing "mount -u -o rw /" ?  I may have omitted this step.

No.  My English is not perfect it seems - my point was that you should never
mount your root fs r/w if you want to do tunefs on it.

> I will re-verify the exact procedure and exact steps in a moment, and
> reply here.
> 
>>> - sysctl kern.geom.debugflags=16
>>> - tunefs -t enable /dev/ada0s1a --- works
>>> - tunefs -p /dev/ada0s1a -- shows TRIM enabled
>>> - reboot
>>
>> I think that at this step your superblock on disk gets re-written with its copy in
>> memory which has never been updated.  But not sure.
> 
> Hmm, I sure hope that isn't the case.

I think that this is the case.

> That would mean the only time a
> person can use tunefs on a root filesystem is when they either do it
> manually during the FreeBSD installation (adding "-t" to the list of
> newfs flags in the filesystem creation UI), or if they boot off of some
> other medium (USB flash drive, CD, PXE, etc.).

Or when your root fs is mounted r/o, which is not as bad as what you listed above.

-- 
Andriy Gapon