Comment # 10 on bug 860067 from Thomas Blume

(In reply to Michal Papis from comment #9)
> also another point missing compared to
> https://bugzilla.opensuse.org/show_bug.cgi?id=908162 is that /tmp is a
> standard directory, it's unfortunate for owners of SSD disks, this directory
> should be mounted as tmpfs so it's both does not use your precious disk and
> is cleaned on rebot - with this added a periodic cleanup is required

A periodic cleanup feature is available in 13.1 as:

systemd-tmpfiles-clean.service

The default configuration file for cleaning up these directories is available
at:

/usr/lib/tmpfiles.d/tmp.conf

It contains the entry:

-->--
# Clear tmp directories separately, to make them easier to override
# SUSE policy: we don't clean those directories
d /tmp 1777 root root -
d /var/tmp 1777 root root -
--<--

So, it is a policy that tmp files cleaning is not enabled by default.
This is conform with earlier versions where you had to configure the tmpfiles
cleaning in /etc/sysconfig/cron:

-->--
# cron.daily can check for old files in tmp-dirs. It will delete all files
# not accessed for more than MAX_DAYS_IN_TMP. If MAX_DAYS_IN_TMP is not set
# or set to 0, this feature will be disabled. 
#
MAX_DAYS_IN_TMP="0"
--<--


So, this isn't a bug, you only need to enable the service and configure it
accordingly.

-> closing