What's with junk in /var/tmp?

[joneall]

I noticed this because when I do a dist-upgrade, I get several messages like this:

Setting up linux-firmware (1.157.18) ...
update-initramfs: Generating /boot/initrd.img-4.13.0-41-generic
rm: cannot remove '/var/tmp/mkinitramfs_clsdCI/usr/share/fonts/truetype/ubuntu': No such file or directory

In all, /var/tmp now contains 180MB of such stuff, dating from last June. Not a whole lot, but ...

sudo ls -l /var/tmp
drwxr-xr-x 2 jon  jon  4096 févr. 20 19:22 audacity-jon
drwx------ 3 jon  jon  4096 mai   17 08:08 kdecache-jon
drwx------ 2 root root 4096 févr. 19  2017 kdecache-root
drwx------ 3 root root 4096 janv. 1 07:53 systemd-private-016643c427734f3ea94156258c0a486f-systemd-timesyncd.service-o2dQ1Z
drwx------ 3 root root 4096 juin   6  2017 systemd-private-038e46f78e01422280300f4af41cce42-colord.service-l6PPuO
...

Some internet sites say I can delete it, but I'd really like to have an idea why it's there first.

[GreyGeek]

5.15. /var/tmp : Temporary files preserved between system reboots

5.15.1. Purpose

The /var/tmp directory is made available for programs that require temporary files or directories that are preserved between system reboots. Therefore, data stored in /var/tmp is more persistent than data in /tmp.

Files and directories located in /var/tmp must not be deleted when the system is booted. Although data stored in /var/tmp is typically deleted in a site-specific manner, it is recommended that deletions occur at a less frequent interval than /tmp.

On my system, Neon User Edition on top of Btrfs, /var/tmp has in it only files created by systemd, and are inaccessible.

[joneall]

It appears that the system cleans out everything over a year old. Guess I'll just stick with that.

Still, I wonder why I get that error from dist-upgrade.