[Bug 1707222] Re: usage of /tmp during boot is not safe due to systemd-tmpfiles-clean

[James Falcon]

Tracked in Github Issues as https://github.com/canonical/cloud-
init/issues/2967

** Bug watch added: github.com/canonical/cloud-init/issues #2967
   https://github.com/canonical/cloud-init/issues/2967

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https://bugs.launchpad.net/bugs/1707222

Title:
  usage of /tmp during boot is not safe due to systemd-tmpfiles-clean

Status in cloud-init:
  Fix Released
Status in cloud-init package in Ubuntu:
  Fix Released
Status in systemd package in Ubuntu:
  Won't Fix

Bug description:
  Earlier this week on Zesty on Azure I saw a cloud-init failure in its 'mount_cb' function.
  That function esentially does:
   a.) make a tmp directory for a mount point
   b.)  mount some filesystem to that mount point
   c.) call a function
   d.) unmount the directory

  What I recall was that access to a file inside the mount point failed during 'c'.
  This seems possible as systemd-tmpfiles-clean may be running at the same time as cloud-init (cloud-init.service in this example).

  
  It seems that this service basically inhibits *any* other service from using tmp files.
  It's ordering statements are only:

    After=local-fs.target time-sync.target
    Before=shutdown.target

  So while in most cases only services that run early in the boot
  process like cloud-init will be affected, any service could have its
  tmp files removed.  this service could take quite a long time to run
  if /tmp/ had been filled with lots of files in the previous boot.

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