react-native cli：启动时出错

react-native cli: error on start up

我按照说明安装了react-native但是

1	$npm start

我有以下错误。

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ERROR Metro Bundler can't listen on port 8081
Loading dependency graph...
npm ERR! Darwin 17.3.0
npm ERR! argv"/usr/local/bin/node""/usr/local/bin/npm""start"
npm ERR! node v7.8.0
npm ERR! npm v4.2.0
npm ERR! code ELIFECYCLE
npm ERR! errno 11
npm ERR! [email protected] start: `node node_modules/react-native/local-
cli/cli.js start`

我想有某种依赖或冲突，有谁知道我怎么弄清楚它是什么？