今天要安装MySQL，在install之前要执行一下upgrate，那么接着就报下面的错误了：
W: GPG error: http://archive.ubuntukylin.com trusty Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY D259B7555E1D3C58
貌似是公钥不可以用了，需要获取新的key，命令如下：
10:02linc@Linc-Ubuntu:~$ sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys D259B7555E1D3C58
Executing: gpg --ignore-time-conflict --no-options --no-default-keyring --secret-keyring /tmp/tmp.JXx8td77hP --trustdb-name /etc/apt/trustdb.gpg --keyring /etc/apt/trusted.gpg --primary-keyring /etc/apt/trusted.gpg --keyserver keyserver.ubuntu.com --recv-keys D259B7555E1D3C58
gpg: requesting key 5E1D3C58 from hkp server keyserver.ubuntu.com
gpg: key 5E1D3C58: public key "Ubuntu Kylin Archive Automatic Signing Key <council@ubuntukylin.com>" imported
gpg: Total number processed: 1
gpg: imported: 1 (RSA: 1)