[systemd-devel] why does nofail imply no After= in /etc/fstab

[Chris Murphy]

On Jan 16, 2014, at 8:25 AM, Kay Sievers <kay at vrfy.org> wrote:

> On Thu, Jan 16, 2014 at 4:19 PM, Lennart Poettering
> <lennart at poettering.net> wrote:
>> On Thu, 16.01.14 16:14, Zbigniew Jędrzejewski-Szmek (zbyszek at in.waw.pl) wrote:
>> 
>>> 
>>> On Thu, Jan 16, 2014 at 03:51:02PM +0100, Lennart Poettering wrote:
>>>> On Wed, 15.01.14 20:20, Zbigniew Jędrzejewski-Szmek (zbyszek at in.waw.pl) wrote:
>>>> 
>>>>> I was a bit surprised that for mount points the dependency
>>>>> Before=local-fs.target is only added when nofail is not used.
>>>>> This seems to be a concious decision (added by Lennart in
>>>>> 155da457, and then survived all the refactorings by Tom
>>>>> and Thomas...). Do we still want this behaviour?
>>>> 
>>>> Well, "nofail" means that we shouldn't bother if the device doesn't show
>>>> up at boot. Now, if we add "After=" for it there, then we will time-out
>>>> on it (though not fail) if something else pulls it in.
>>>> 
>>>> I figure this is a question what nofail really should mean: "never wait
>>>> for it, never fail for it" (which is the status quo), or just "usually
>>>> don't wait, never fail for it" (which would be the change if we added
>>>> After= in). I am tempted to say that the status quo is more likely what
>>>> people would expect, no?
>>> 
>>> The problem is that with current boot speeds, "usually don't wait" means
>>> that it shows up at some "upredictable" time. With a bit of luck, users
>>> might be able to log in before such mount points which are declared in
>>> /etc/fstab are mounted. I think that's unexpected, because it goes againt
>>> the general rule that things declared in /etc/fstab (w/o automount or noauto)
>>> are mounted at boot.
>> 
>> I'd argue that "nofail" is precisely what the admin can use to *enable*
>> this race. If it should be avoided to allow the user to log in before
>> the device has shown up and is hooked in the admin should not have used
>> "nofail"...
>> 
>>> I'd prefer to keep things orthogonal. This feels like an "optimization"
>>> that it user visible. We should rather encourage people to use automounts
>>> if the don't want to wait for the mountpoint to come up.
>> 
>> I am pretty sure people would be annoyed by this change of behaviour,
>> simply because every boot would still delay for 90s if the device is not
>> plugged in. I have the suspicion that people would really assume that
>> using "nofail" would make their system boot-up cleanly, without delays
>> if the file system cannot be found -- and that expection is something
>> we'd not fulfill?
> 
> man mount 8:
> nofail -- Do not report errors for this device if it does not exist.
> 
> Right, we cannot really re-define this. It's use is established since years.
> Used for things like isci, which is often not available at bootup.


Although with faster boot times, a device in fstab not existing is probably increasingly common. What about splitting the scheduling of .mount jobs such that /sysroot happens early, and everything else listed in fstab happens much later, to give the underlying device every opportunity to appear before the attempt?


Chris Murphy