Run 'do-release-upgrade' to upgrade to it.

ひさびさにラズパイにログインして、こんなメッセージが表示されていたら、

Welcome to Ubuntu 16.04.7 LTS (GNU/Linux 4.4.38-v7+ armv7l)

* Documentation: https://help.ubuntu.com
* Management: https://landscape.canonical.com
* Support: https://ubuntu.com/advantage

999 updates can be applied immediately.
To see these additional updates run: apt list --upgradable

New release '18.04.5 LTS' available.
Run 'do-release-upgrade' to upgrade to it.

『ふむ、じゃあ、アップグレードしてみようかね』って思うじゃないですか？

で、私から6時間も作業時間を奪った挙句に、

The upgrade has aborted. The upgrade needs a total of 2,827 M free space on disk '/'. Please free at least an additional 39.8 M of disk space on '/'. Empty your trash and remove temporary packages of former installations using 'sudo apt-get clean'. The upgrade has aborted. The upgrade needs a total of 49.5 M free space on disk '/boot'. Please free at least an additional 4,309 k of disk space on '/boot'. You can remove old kernels using 'sudo apt autoremove' and you could also set COMPRESS=xz in /etc/initramfs-tools/initramfs.conf to reduce the size of your initramfs.

って、メッセージを出すのは、ちょっと酷くない？ って思うんですよね。
(一応、上記の指示は、全部やってみたよ、勿論)

『そんな潤沢なリソース持っとらんわ！』と捨て台詞を吐いて、今週末を終えました。