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

[Nick Rosbrook]

> how would it impact you if it was NOT cleaned at reboot?

I just like it. It's easier for me to keep track in my head that "oh,
this file in /tmp will only be around until I reboot", as opposed to
trying to keep track of the actual age of a file. To be clear, I am not
suggesting that my use case is strong argument for keeping the current
default (I will happily write an /etc/tmpfiles.d/tmp.conf drop-in to
meet my preference if needed). Just pointing out that there might be a
range of preferences on the default handling of /tmp.

Also, you may have already come across this, but if not, this is the
Debian bug that resulted in the current default:
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=675422.

If you think it would be best for most Ubuntu users to change the
current default, then we should go with your suggested change. If the
motivation is mostly about your schroot use case, then I would suggest
either modifying schroot to do what you need, or using
/etc/tmpfiles.d/tmp.conf.

** Bug watch added: Debian Bug tracker #675422
   https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=675422

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

Title:
  systemd /tmp cleaning is suboptimal

Status in systemd package in Ubuntu:
  New

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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