nixos/xl2tpd: prefer 'install' over 'chmod/chown' (#302388)

      wantedBy = [ "multi-user.target" ];

      preStart = ''

        mkdir -p -m 700 /etc/xl2tpd

        install -m 700 -d /etc/xl2tpd/ppp

        pushd /etc/xl2tpd > /dev/null

        mkdir -p -m 700 ppp

        [ -f ppp/chap-secrets ] || cat > ppp/chap-secrets << EOF

        [ -f /etc/xl2tpd/ppp/chap-secrets ] || install -m 600 -o root -g root /dev/stdin /etc/xl2tpd/ppp/chap-secrets <<EOF

        # Secrets for authentication using CHAP

        # client	server	secret		IP addresses

        #username	xl2tpd	password	*

        EOF

        chown root:root ppp/chap-secrets

        chmod 600 ppp/chap-secrets

        # The documentation says this file should be present but doesn't explain why and things work even if not there:

        [ -f l2tp-secrets ] || (echo -n "* * "; ${pkgs.apg}/bin/apg -n 1 -m 32 -x 32 -a 1 -M LCN) > l2tp-secrets

        chown root:root l2tp-secrets

        chmod 600 l2tp-secrets

        popd > /dev/null

        [ -f /etc/xl2tpd/l2tp-secrets ] || install -m 600 -o root -g root <(echo -n "* * "; ${pkgs.apg}/bin/apg -n 1 -m 32 -x 32 -a 1 -M LCN) /etc/xl2tpd/l2tp-secrets

        mkdir -p /run/xl2tpd

        chown root:root /run/xl2tpd

        chmod 700       /run/xl2tpd

        install -m 701 -o root -g root -d /run/xl2tpd

      '';

      serviceConfig = {