man 명령어로 사용법 읽고 싶은데 나오지 않네요.
해결방법.

https://unix.stackexchange.com/questions/484705/see-man-7-undocumented-for-help-when-manual-pages-are-not-available-wsl-core

위 주소에서 읽어보니.

The first two lines of /etc/dpkg/dpkg.cfg.d/excludes

# Drop all man pages
path-exclude=/usr/share/man/*

`

# Drop all man pages
path-exclude=/usr/share/man/*

cause all man pages to be dropped when packages are installed.

To make man pages available, you’ll have to comment the second line out:

# Drop all man pages
# path-exclude=/usr/share/man/*

then re-install any package for which you want the man pages:

apt --reinstall install man-db coreutils

to restore the man and ls man pages (among others).

Drop 되는 장소에 메뉴얼이 다 들어가니, 그 곳 주석처리하고 다시 설치하라는 말이네요. 따라서 하니 이제 잘 됣니다.