Nix's man command does not see '/usr/share/man'

I’ve installed nix in my Arch linux

curl https://nixos.org/nix/install | sh

After reboot, man does not find manual pages in system /usr/share/man

a@a ~> which man
/home/a/.nix-profile/bin/man

a@a ~> man which
No manual entry for which

a@a ~> which manpath
/home/a/.nix-profile/bin/manpath

a@a ~> manpath
/home/a/.local/share/man:/home/a/.nix-profile/share/man:/usr/local/man

a@a ~> /usr/bin/manpath
/home/a/.local/share/man:/home/a/.nix-profile/share/man:/usr/local/man:/usr/local/share/man:/usr/share/man

a@a ~> /usr/bin/man nix-env # It's ok.
...
a@a ~> /usr/bin/man which # Also It's ok.
...
a@a ~> 
1 Like