So I ran a stupid command as root (DO NOT RUN THIS)
# chown -R root:root /{usr,lib,var,etc,bin,sbin,tools}
So... oops. I happened to have a root shell open (from when I caused this), so I was able to get sudo working by doing
# chown root:root /usr/bin/sudo
# chmod 4755 /usr/bin/sudo
Yay, sudo works again. I wanted to install a package (ncdu), so I ran sudo apt-get install ncdu.
$ sudo apt-get install ncdu
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
The following NEW packages will be installed:
ncdu
0 upgraded, 1 newly installed, 0 to remove and 0 not upgraded.
Need to get 0 B/43.4 kB of archives.
After this operation, 106 kB of additional disk space will be used.
Selecting previously unselected package ncdu.
(Reading database ... 233654 files and directories currently installed.)
Preparing to unpack .../ncdu_1.15.1-1_amd64.deb ...
Unpacking ncdu (1.15.1-1) ...
Setting up ncdu (1.15.1-1) ...
Processing triggers for man-db (2.9.4-2) ...
/usr/bin/mandb: can't chmod /var/cache/man/CACHEDIR.TAG: Operation not permitted
/usr/bin/mandb: can't remove /var/cache/man/CACHEDIR.TAG: Permission denied
/usr/bin/mandb: fopen /var/cache/man/1053532: Permission denied
/usr/bin/mandb: can't chmod /var/cache/man/es/CACHEDIR.TAG: Operation not permitted
/usr/bin/mandb: can't remove /var/cache/man/es/CACHEDIR.TAG: Permission denied
/usr/bin/mandb: fopen /var/cache/man/es/1053532: Permission denied
/usr/bin/mandb: can't chmod /var/cache/man/zh_TW/CACHEDIR.TAG: Operation not permitted
/usr/bin/mandb: can't remove /var/cache/man/zh_TW/CACHEDIR.TAG: Permission denied
/usr/bin/mandb: fopen /var/cache/man/zh_TW/1053532: Permission denied
/usr/bin/mandb: can't chmod /var/cache/man/fi/CACHEDIR.TAG: Operation not permitted
/usr/bin/mandb: can't remove /var/cache/man/fi/CACHEDIR.TAG: Permission denied
/usr/bin/mandb: fopen /var/cache/man/fi/1053532: Permission denied
/usr/bin/mandb: can't chmod /var/cache/man/de/CACHEDIR.TAG: Operation not permitted
/usr/bin/mandb: can't remove /var/cache/man/de/CACHEDIR.TAG: Permission denied
/usr/bin/mandb: fopen /var/cache/man/de/1053532: Permission denied
/usr/bin/mandb: can't chmod /var/cache/man/uk/CACHEDIR.TAG: Operation not permitted
/usr/bin/mandb: can't remove /var/cache/man/uk/CACHEDIR.TAG: Permission denied
/usr/bin/mandb: fopen /var/cache/man/uk/1053532: Permission denied
/usr/bin/mandb: can't chmod /var/cache/man/sr/CACHEDIR.TAG: Operation not permitted
/usr/bin/mandb: can't remove /var/cache/man/sr/CACHEDIR.TAG: Permission denied
/usr/bin/mandb: fopen /var/cache/man/sr/1053532: Permission denied
/usr/bin/mandb: can't chmod /var/cache/man/sl/CACHEDIR.TAG: Operation not permitted
/usr/bin/mandb: can't remove /var/cache/man/sl/CACHEDIR.TAG: Permission denied
/usr/bin/mandb: fopen /var/cache/man/sl/1053532: Permission denied
/usr/bin/mandb: can't chmod /var/cache/man/nb/CACHEDIR.TAG: Operation not permitted
/usr/bin/mandb: can't remove /var/cache/man/nb/CACHEDIR.TAG: Permission denied
/usr/bin/mandb: fopen /var/cache/man/nb/1053532: Permission denied
/usr/bin/mandb: can't chmod /var/cache/man/pt/CACHEDIR.TAG: Operation not permitted
/usr/bin/mandb: can't remove /var/cache/man/pt/CACHEDIR.TAG: Permission denied
/usr/bin/mandb: fopen /var/cache/man/pt/1053532: Permission denied
/usr/bin/mandb: can't chmod /var/cache/man/ru/CACHEDIR.TAG: Operation not permitted
/usr/bin/mandb: can't remove /var/cache/man/ru/CACHEDIR.TAG: Permission denied
/usr/bin/mandb: fopen /var/cache/man/ru/1053532: Permission denied
/usr/bin/mandb: can't chmod /var/cache/man/ko/CACHEDIR.TAG: Operation not permitted
/usr/bin/mandb: can't remove /var/cache/man/ko/CACHEDIR.TAG: Permission denied
/usr/bin/mandb: fopen /var/cache/man/ko/1053532: Permission denied
/usr/bin/mandb: can't chmod /var/cache/man/it/CACHEDIR.TAG: Operation not permitted
/usr/bin/mandb: can't remove /var/cache/man/it/CACHEDIR.TAG: Permission denied
/usr/bin/mandb: fopen /var/cache/man/it/1053532: Permission denied
/usr/bin/mandb: can't chmod /var/cache/man/fr/CACHEDIR.TAG: Operation not permitted
/usr/bin/mandb: can't remove /var/cache/man/fr/CACHEDIR.TAG: Permission denied
/usr/bin/mandb: fopen /var/cache/man/fr/1053532: Permission denied
/usr/bin/mandb: can't chmod /var/cache/man/et/CACHEDIR.TAG: Operation not permitted
/usr/bin/mandb: can't remove /var/cache/man/et/CACHEDIR.TAG: Permission denied
/usr/bin/mandb: fopen /var/cache/man/et/1053532: Permission denied
/usr/bin/mandb: can't chmod /var/cache/man/ca/CACHEDIR.TAG: Operation not permitted
/usr/bin/mandb: can't remove /var/cache/man/ca/CACHEDIR.TAG: Permission denied
/usr/bin/mandb: fopen /var/cache/man/ca/1053532: Permission denied
/usr/bin/mandb: can't chmod /var/cache/man/tr/CACHEDIR.TAG: Operation not permitted
/usr/bin/mandb: can't remove /var/cache/man/tr/CACHEDIR.TAG: Permission denied
/usr/bin/mandb: fopen /var/cache/man/tr/1053532: Permission denied
/usr/bin/mandb: can't chmod /var/cache/man/nl/CACHEDIR.TAG: Operation not permitted
/usr/bin/mandb: can't remove /var/cache/man/nl/CACHEDIR.TAG: Permission denied
/usr/bin/mandb: fopen /var/cache/man/nl/1053532: Permission denied
/usr/bin/mandb: can't chmod /var/cache/man/fr.UTF-8/CACHEDIR.TAG: Operation not permitted
/usr/bin/mandb: can't remove /var/cache/man/fr.UTF-8/CACHEDIR.TAG: Permission denied
/usr/bin/mandb: fopen /var/cache/man/fr.UTF-8/1053532: Permission denied
/usr/bin/mandb: can't chmod /var/cache/man/hu/CACHEDIR.TAG: Operation not permitted
/usr/bin/mandb: can't remove /var/cache/man/hu/CACHEDIR.TAG: Permission denied
/usr/bin/mandb: fopen /var/cache/man/hu/1053532: Permission denied
/usr/bin/mandb: can't chmod /var/cache/man/fr.ISO8859-1/CACHEDIR.TAG: Operation not permitted
/usr/bin/mandb: can't remove /var/cache/man/fr.ISO8859-1/CACHEDIR.TAG: Permission denied
/usr/bin/mandb: fopen /var/cache/man/fr.ISO8859-1/1053532: Permission denied
/usr/bin/mandb: can't chmod /var/cache/man/sv/CACHEDIR.TAG: Operation not permitted
/usr/bin/mandb: can't remove /var/cache/man/sv/CACHEDIR.TAG: Permission denied
/usr/bin/mandb: fopen /var/cache/man/sv/1053532: Permission denied
/usr/bin/mandb: can't chmod /var/cache/man/id/CACHEDIR.TAG: Operation not permitted
/usr/bin/mandb: can't remove /var/cache/man/id/CACHEDIR.TAG: Permission denied
/usr/bin/mandb: fopen /var/cache/man/id/1053532: Permission denied
/usr/bin/mandb: can't chmod /var/cache/man/el/CACHEDIR.TAG: Operation not permitted
/usr/bin/mandb: can't remove /var/cache/man/el/CACHEDIR.TAG: Permission denied
/usr/bin/mandb: fopen /var/cache/man/el/1053532: Permission denied
/usr/bin/mandb: can't chmod /var/cache/man/pt_BR/CACHEDIR.TAG: Operation not permitted
/usr/bin/mandb: can't remove /var/cache/man/pt_BR/CACHEDIR.TAG: Permission denied
/usr/bin/mandb: fopen /var/cache/man/pt_BR/1053532: Permission denied
/usr/bin/mandb: can't chmod /var/cache/man/ro/CACHEDIR.TAG: Operation not permitted
/usr/bin/mandb: can't remove /var/cache/man/ro/CACHEDIR.TAG: Permission denied
/usr/bin/mandb: fopen /var/cache/man/ro/1053532: Permission denied
/usr/bin/mandb: can't chmod /var/cache/man/zh_CN/CACHEDIR.TAG: Operation not permitted
/usr/bin/mandb: can't remove /var/cache/man/zh_CN/CACHEDIR.TAG: Permission denied
/usr/bin/mandb: fopen /var/cache/man/zh_CN/1053532: Permission denied
/usr/bin/mandb: can't chmod /var/cache/man/cs/CACHEDIR.TAG: Operation not permitted
/usr/bin/mandb: can't remove /var/cache/man/cs/CACHEDIR.TAG: Permission denied
/usr/bin/mandb: fopen /var/cache/man/cs/1053532: Permission denied
/usr/bin/mandb: can't chmod /var/cache/man/gl/CACHEDIR.TAG: Operation not permitted
/usr/bin/mandb: can't remove /var/cache/man/gl/CACHEDIR.TAG: Permission denied
/usr/bin/mandb: fopen /var/cache/man/gl/1053532: Permission denied
/usr/bin/mandb: can't chmod /var/cache/man/da/CACHEDIR.TAG: Operation not permitted
/usr/bin/mandb: can't remove /var/cache/man/da/CACHEDIR.TAG: Permission denied
/usr/bin/mandb: fopen /var/cache/man/da/1053532: Permission denied
/usr/bin/mandb: can't chmod /var/cache/man/pl/CACHEDIR.TAG: Operation not permitted
/usr/bin/mandb: can't remove /var/cache/man/pl/CACHEDIR.TAG: Permission denied
/usr/bin/mandb: fopen /var/cache/man/pl/1053532: Permission denied
/usr/bin/mandb: can't chmod /var/cache/man/ja/CACHEDIR.TAG: Operation not permitted
/usr/bin/mandb: can't remove /var/cache/man/ja/CACHEDIR.TAG: Permission denied
/usr/bin/mandb: fopen /var/cache/man/ja/1053532: Permission denied
Clearly I didn't do enough to fix my system. I'd prefer not to reinstall the OS if possible, but I have a root shell (it's a physical laptop in front of me), so I'm wondering how to fix apt so I can install packages again. I'm using Kubuntu 21.10.
