add param fetch command

cli/cmd.go

@@ -114,6 +114,7 @@ var Commands = []*cli.Command{
 	chainCmd,
 	clientCmd,
 	createMinerCmd,
+	fetchParamCmd,
 	mpoolCmd,
 	netCmd,
 	paychCmd,

cli/params.go

@@ -0,0 +1,19 @@
+package cli
+
+import (
+	"github.com/filecoin-project/go-lotus/build"
+	"golang.org/x/xerrors"
+	"gopkg.in/urfave/cli.v2"
+)
+
+var fetchParamCmd = &cli.Command{
+	Name:  "fetch-params",
+	Usage: "Fetch proving parameters",
+	Action: func(cctx *cli.Context) error {
+		if err := build.GetParams(true); err != nil {
+			return xerrors.Errorf("fetching proof parameters: %w", err)
+		}
+
+		return nil
+	},
+}