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Date:      Tue, 21 Apr 2020 16:09:39 +0200
From:      Polytropon <freebsd@edvax.de>
To:        Scott <freebsd-lists-5@thismonkey.com>
Cc:        freebsd-questions@freebsd.org
Subject:   Re: Should fsck honour "failok" in fstab as mount does?
Message-ID:  <20200421160939.aa2fbd89.freebsd@edvax.de>
In-Reply-To: <20200421135406.GA74559@thismonkey.com>
References:  <20200421071319.GA98163@thismonkey.com> <20200421153144.d45a889b.freebsd@edvax.de> <20200421135406.GA74559@thismonkey.com>

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On Tue, 21 Apr 2020 23:54:06 +1000, Scott wrote:
> On Tue, Apr 21, 2020 at 03:31:44PM +0200, Polytropon wrote:
> > On Tue, 21 Apr 2020 17:13:20 +1000, Scott wrote:
> > work. The file /etc/fstab is the filesystem table intended
> > for use with mount; the fact that fsck uses it is just a nice
> > side effect, but not its primary use. That's why the options
> > field is intended for the mount command.
> 
> True, but that doesn't preclude fsck's use of any hints it may glean from 
> /etc/fstab.

The 6th field of /etc/fstab, the "fsck column", is intnded
to be used by fsck, as per the manual, but of course this
does not say anything about "what to do in case of problems".



> > The effect that the system drops into single-user mode is
> > also intended. When fsck is invoked - upon filesystem error -
> 
> Sure, but the point of `failok' is to continue booting even if the so 
> optioned filesystem cannot mount for whatever reason.  Unfortunately fsck 
> makes no use of this indication and prevents booting.  These two commands, 
> fsck and mount need to work in tandem.

Yes, that is correct. However, it looks like "noauto" is
basically what you're searching for. During the boot process,
specific filesystems are gathered from /etc/fstab, and their
consistency is tested before mounting, afterwards they are
mounted. Later mounting and manual mounting is possible too,
even with filesystems specified in /etc/fstab, but with the
"noauto" mount option - in this case, fsck won't even look
at them, except mount itself could complain ("so-and-so was
not properly dismounted").

So the consensus seems to be: If you don't want fsck to look
at a filesystem and maybe stop the boot process, use "noauto".
If you want it to be mounted later on, do so manually (with
of of the methods I mentioned, or entirely interactively).



> > If you don't want fsck to stumble upon a damaged filesystem,
> > do not include it in /etc/fstab. You can still use a custom
> > rc.d-style script or an entry in /etc/rc.local if you wish
> > to "maybe mount" non-vital or optional filesystems later on.
>  
> Sure, but why would you want to do it that way?  The same could be said when 
> the `failok' option was not available to mount.

Right, this approach does not even require "failok".



> Consider the situation where a device specified in /etc/fstab is not present 
> during boot, say a USB stick.  You've added the `failok' option to its 
> /etc/fstab entry, declaring that if you can't mount the device, ignore the 
> error and continue. fsck will still drop into single user mode.  Does that 
> make sense?

Yes, because the entry in /etc/fstab says the device is _required_
during the boot process - any non-"noauto" entry is to be checked
and mounted during system boot. The opposite of "noauto" is "auto",
and it is the default - meaning, according to the manual: "to be
automatically mounted at system startup". So any of such entries
is considered "required for booting".

I think you're expecting "failok" to do something it is not
intended to do.



-- 
Polytropon
Magdeburg, Germany
Happy FreeBSD user since 4.0
Andra moi ennepe, Mousa, ...



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