Wednesday, 13 January 2016

Re: RFC on Cloud Images: Make /tmp a tmpfs

Excerpts from Martin Pitt's message of 2016-01-13 14:00:16 -0800:
> 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.
>

You know they have these new disks that don't "spin"... ;-)

> 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.

MySQL and MariaDB are a perfect example of /tmp abuse. If you alter a
table in the InnoDB storage engine that can be rebuilt on-line, it will
create a copy of the table in the server's tmpdir. Currently these both
default tmpdir to /tmp. I've been bit by this several times when on
boxes with tmpfs of 1GB.

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