Ubuntu update appear GPG problem

Problem:

sudo apt-get update

[sudo] password for juanecho:
获取：1 http://mirrors.163.com trusty InRelease [269 B]
获取：2 http://mirrors.163.com trusty-security InRelease [269 B]               
99% [1 InRelease gpgv 269 B] [正在等待报头]Splitting up /var/lib/apt/lists/parti忽略 http://archive.ubuntukylin.com:10006 trusty InRelease and signature failed
忽略 http://mirrors.163.com trusty InRelease                                
E: GPG 错误：http://mirrors.163.com trusty InRelease: Clearsigned file isn't valid, got 'NODATA' (does the network require authentication?)
juanecho@juanechoPC:~$ sudo apt-get update
获取：1 http://mirrors.163.com trusty InRelease [269 B]
98% [1 InRelease gpgv 269 B] [正在连接 mirrors.163.com (123.58.173.186)] [�Splitting up /var/lib/apt/lists/partial/mirrors.163.com_ubuntu_dists_trusty_InRelease忽略 http://mirrors.163.com trusty InRelease                                   
E: GPG 错误：http://mirrors.163.com trusty InRelease: Clearsigned file isn't valid, got 'NODATA' (does the network require authentication?)

Solution:

sudo apt-get clean

sudo apt-get update