[ubuntu-cloud] RFC on Cloud Images: Make /tmp a tmpfs

[Steve Langasek]

On Wed, Jan 13, 2016 at 11:00:16PM +0100, Martin Pitt wrote:
> Ben Howard [2016-01-13 14:26 +0200]:
> > On the Ubuntu Cloud Images, we have a request to make /tmp a tmpfs. The
> > rationale, from the bug:
> >  * Performance - much faster read/write access to data in /tmp
> >  * Security - sensitive data would be cleared from memory on boot,
> >    rather than written (leaked) to disk -- important for encryption
> >    scenarios

> > Since the Ubuntu Cloud Images are used by a wide number of users, I
> > wanted to gather feedback and gather consensus on whether or not we
> > should make this change.

> I really wish we would do this in general for new installs, at least
> as the first thing after releasing 16.04 LTS. I also do this on my
> boxes, not only for the reasons above [1], but also because it is much
> more power efficient -- as I literally work in /tmp a lot of my time
> the disk doesn't need to spin up often.

> The main reason AFAIK why we didn't yet do that was the concern that
> there is some broken software out there which potentially dumps really
> large files into /tmp (yes firefox, I'm looking at YOU!). These would
> need to be fixed to go to /var/tmp. This is a chicken-and-egg problem,
> though: We won't find out what's broken until we actually enable it on
> real-life installations. This problem applies to cloud image use cases
> just as much as desktop or "classic" servers.

> My gut feeling is that we should do it if there is ≥ 4 GB RAM, so that
> /tmp as at least 2 GB of space (That should be a rather simple
> installer/cloud-init decision?). We don't want to do this on small
> embedded devices with 512 MB of RAM or so, but there is absolutely no
> reason to not do it on beefy servers or laptops.

As a data point, I used to have my /tmp on tmpfs while I still had a
spinning disk, in order to address the power usage issues of disk flushing.
I found it to be a least-bad option which led to serious degradation of
desktop interactivity in the face of even moderate memory usage (at the
time, with 4GB RAM), and not because of excessive /tmp usage.

And as others in this thread have noted, this same problem can occur in
cloud instances.

-- 
Steve Langasek                   Give me a lever long enough and a Free OS
Debian Developer                   to set it on, and I can move the world.
Ubuntu Developer                                    http://www.debian.org/
slangasek at ubuntu.com                                     vorlon at debian.org
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