When a new page is added using man/update-man-rules, ninja doesn't know
about the new target until a build is initiated, so build/man/man and
build/man/html would fail. Force a trivial build to regenerate the rules
before calling 'ninja -t'.
Man page generation is generally very slow. I prefer to use -Dman=false when
developing systemd, and only build specific pages when introducing changes.
Those two little helper tools make it easy:
$ build/man/man systemd.link
$ build/man/html systemd.link
will show systemd.link.8 and systemd.link.html from the build directory build/.
Frantisek Sumsal