[Bug 1533639] [NEW] [ubuntu-cpc] please make /tmp a tmpfs in RAM

[Ben Howard]

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After considering the robust discussion, I would like to propose that
we move forward with this change via Cloud-init with some sane
defaults (i.e. it is _NOT_ running in a container and memory is
greater than 2GB of RAM).

Given that Xenial is in Alpha, now is the time to make this change.
The reality is that without actually making the change we can't and
won't be able to fully scope the impact.

So with that, I think that having Cloud-init configure /tmp as tmpfs,
while giving the user the ability to change it, is a sane path
forward. In the event that we have serious or unintended consequences,
we can revert pre-release or even via an SRU if necessary.
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https://bugs.launchpad.net/bugs/1533639

Title:
  [ubuntu-cpc] please make /tmp a tmpfs in RAM

Status in livecd-rootfs package in Ubuntu:
  Triaged

Bug description:
  In Ubuntu, we have always cleared /tmp on every boot.

  As such, on servers, by default /tmp should actually be a tmpfs
  entirely in RAM, when there is enough memory in the system.  This
  threshold should be configurable by the end user (in cloud-init?), and
  default threshold of ~3GB.

  Read about tmpfs here:
  https://www.kernel.org/doc/Documentation/filesystems/tmpfs.txt

  This has several advantages, mainly:
   * Performance - much faster read/write access to data in /tmp
     - especially if your disk is spinning media
     - and if you're on SSD, this feature extends the life of your flash by reducing your NAND flash writes
   * Security - sensitive data would be cleared from memory on boot, rather than written (leaked) to disk -- important for encryption scenarios
   * Power consumption - storing information in memory is more energy efficient than reading and writing to disk

  In scenarios where more space in /tmp is needed than available, one
  can compliment that tmpfs with 'sudo apt-get install swapspace' which
  will dynamically create/delete swapfile as necessary.  See:
  http://manpg.es/swapspace

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