[Bug 2019026] Re: systemd /tmp cleaning is suboptimal

[Paride Legovini]

FWIW I agree with Nick's preference (clean at boot && clean files older
than 30d). Maybe we could make that 40d, as 30d is likely to be a time
interval at which a lot of periodic things happen (e.g. an off-site
backup). A retention period >30d is less likely be synchronized with it
in an unlucky way.

Mounts with relatime (the default) update the atime unconditionally if
the previous atime is >1day old, so no issues with that.

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https://bugs.launchpad.net/bugs/2019026

Title:
  systemd /tmp cleaning is suboptimal

Status in systemd package in Ubuntu:
  Confirmed

Bug description:
  Historically on Debian and Ubuntu, before systemd, the default
  handling of /tmp was to periodically, and at boot, remove all
  files/directories older than 30 days; and leave other contents alone.

  With the move to systemd, the "default" (really, hard-coded in
  /usr/lib/tmpfiles.d/tmp.conf) is to not clean /tmp periodically, but
  at boot to remove all contents.

  This is suboptimal for two reasons.

  By cleaning /tmp *only* at boot, if a system makes heavy use of /tmp
  and has lots of inodes under it, possibly due to failures of some
  process to clean up after itself, at boot the system will be
  unavailable for an unnecessarily long time while these files are
  removed.

  By cleaning *all* files under /tmp, this makes a reboot an Event where
  in-progress files may be unnecessarily lost.

  While the FHS does not *guarantee* that files under /tmp will persist
  across boot (because /tmp may be a tmpfs), it also does not *require*
  that /tmp be cleared on boot.

     Although data stored in /tmp may be deleted in a site-specific
     manner, it is recommended that files and directories located in
     /tmp be deleted whenever the system is booted.

     FHS added this recommendation on the basis of historical
     precedent and common practice, but did not make it a
     requirement because system administration is not within the
     scope of this standard.

  I therefore believe the correct value for /usr/lib/tmpfiles.d/tmp.conf
  to restore past behavior is 'd /tmp 1777 root root 30d'.

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