Using TMPFS for /tmp and /var/run?

[Adrian Chadd]

Let me tell you a story.

Someone decided that ext4 could have a decent speed up if it
implemented the posix standard for not flushing files on close().
After all, if you needed it to be guaranteed to be written to disk,
you would call a flush routine first, before you called close().

So they did this.

Then people testing out ext4 discovered that upon crash, their
kde/gnome profiles were corrupted.

Why? Because KDE/Gnome authors hadn't ever called flush before
close(), and they weren't the only ones. They didn't read the
standard, they only used the system and fixed bugs whenever their
system behaved against their expectations. They didn't notice that the
system was being different from the standard.

Guess what ext4 did? :)

Don't mis-estimate POLA.


Adrian


On 30 March 2012 10:56, Chris Rees <crees at freebsd.org> wrote:
> On 30 March 2012 17:31, C. P. Ghost <cpghost at cordula.ws> wrote:
>> On Fri, Mar 30, 2012 at 3:18 PM,  <sthaug at nethelp.no> wrote:
>>>> > However, if you always want to use tmpfs instead of stable storage,
>>>> please do not.  Some people expect /tmp to be persistent.  This is why
>>>> /etc/defaults/rc.conf has clear_tmp_enable="NO".  Changing this would break
>>>> the POLA.
>>>> >
>>>> This is a mistake.
>>>>
>>>> The default should be clear_tmp_enable="YES"
>>>> if only to uncover those broken configurations that expect /tmp to be
>>>> persistent.
>>>
>>> If you want to break POLA and make a lot of people angry, sure.
>>> Otherwise no.
>>
>> I couldn't agree more. Not clearing /tmp on reboot has been
>> the norm for way too long and it is too late to change now.
>> It's not just POLA, it also involves deleting data of unaware
>> users, and that should be avoided.
>>
>> Anyone willing to change policy w.r.t. /tmp can do so on their
>> own machines. Nothing is preventing them from doing so.
>> But by changing defaults, one should err on the side of
>> caution and remain conservative, IMHO.
>
> >From man hier:
>
> /tmp/      temporary files that are not guaranteed to persist across
> system reboots
>
> This assumption that people often make 'People will be astonished by
> this'-- I would like to have someone speak up and actually say "Yes, I
> use *temporary* directories for long-term storage" rather than the
> assumption that they are around.
>
> Software that assumes this should be fixed, and it won't be until the
> bug is exposed (I'll look at eaccelerator-- it probably should store
> its cache in /var/db).
>
> Maintaining the status quo because of some hypothetical scenario isn't
> really productive.
>
> Chris
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