I'm trying to upgrade my Debian from Jessie to Stretch. apt-get upgrade worked fine. Half-way during apt-get dist-upgrade I got some errors that the installation [I'm not sure at which step, but some step after downloading] couldn't create pipes because there was no space left on the device. I checked and my root filesystem is running out of inodes. /var and /home are on different filesystems, and have plenty of space/inodes. /tmp is FORCRYINGOUTLOUD not mounted as tmpfs, and "systemctl enable tmp.mount" says the file doesn't exist. (Thank you, systemd.)
Is my only option rebuilding a filesystem with more inodes, or is there some other thing I could try?
[update]
My system has become severely crippled (i.e. only rescue mode, even unable to establish an internet connection). Unless some guru likes the challenge of bringing this system back from the dead, I will reinstall. So hint for people running into this problem in the future: do not reboot.

If you can't delete sufficient files you will have to reformat the filesystem.

I don't do Debian, but if /tmp ain't on tmpfs, it ain't the fault of systemd - I've been using it on other systems for years. Perhaps you should give the (Devian) devs a nudge.

Run this command to find where there hidden. Maybe a tmp dir. Then delete them.

My system wasn't dead; I just didn't configure /tmp properly i.e. typo in fstab. I was peeved, because I was told systemctl enable tmp.mount would suffice. Instead you have to edit fstab, which might have been obvious, if there wasn't systemd. Devuan is a commendable project, but there are too many borderline unsupported programs I use already.
So the main difficulty was that /var and /home, the main candidates for pruning, had their own filesystem. I removed packages that were already queued for removal with "dpkg -r {package names}". Also I looked for programs as candidates for removal, and the Steam launcher was a good one. There weren't any other obvious contenders; it was the only program that had many files in a single package.
Eventually I used a live disk. With that I could relocate /usr to another partition. (gdisk, mkfs, cp -a, edit fstab). NB: I made a back-up of my root partition BUT I should have made a back-up of /var too, since it was on another partition. I wanted to update my system before moving it to a new filesystem/partition, because I wanted to use the new inline_data support for ext4. (I had to go through most of the trouble anyway.)