gn: command not found 有大佬懂吗,求助

ubuntu 16.04,在中文官网下载webrtc,depot_tools,按照官网步骤,一模一样,环境变量都设置过了

export WORKSPACE=`pwd`
export PATH=$PATH:$WORKSPACE/depot_tools
cd $WORKSPACE/webrtc/src

执行 gn gen out/Release “–args=is_debug=false” 提示报错gn: command not found,有大佬懂吗,求助