最近在用add-apt-repository添加源时，常常出现以下错误，导致一些第三方源的软件无法安装。
seagull@seagull-desktop:~$ sudo add-apt-repository ppa:shawn-p-huang/ppa Executing: gpg --ignore-time-conflict --no-options --no-default-keyring --secret-keyring /etc/apt/secring.gpg --trustdb-name /etc/apt/trustdb.gpg --keyring /etc/apt/trusted.gpg --primary-keyring /etc/apt/trusted.gpg --keyserver keyserver.ubuntu.com --recv AAAD1D3563E5A736A4F561EE884D6308E89713C4 gpg: requesting key E89713C4 from hkp server keyserver.ubuntu.com gpgkeys: HTTP fetch error 7: couldn't connect to host gpg: no valid OpenPGP data found. gpg: Total number processed: 0
原因：
keyserver.ubuntu.com使用非标准的11371端口，而一般公司的防火墙都屏蔽掉了该端口，而允许标准的80端口。
所以可以以如下方式强行使用80端口添加软件源：
seagull@seagull-desktop:~$ sudo apt-key adv --recv-keys --keyserver hkp://keyserver.ubuntu.com:80 AAAD1D3563E5A736A4F561EE884D6308E89713C4
红色部分是你要请求的Key.
通过如上方式你可成功导入key.
seagull@seagull-desktop:~$ sudo apt-key adv --recv-keys --keyserver hkp://keyserver.ubuntu.com:80 AAAD1D3563E5A736A4F561EE884D6308E89713C4 Executing: gpg --ignore-time-conflict --no-options --no-default-keyring --secret-keyring /etc/apt/secring.gpg --trustdb-name /etc/apt/trustdb.gpg --keyring /etc/apt/trusted.gpg --primary-keyring /etc/apt/trusted.gpg --recv-keys --keyserver hkp://keyserver.ubuntu.com:80 AAAD1D3563E5A736A4F561EE884D6308E89713C4 gpg: requesting key E89713C4 from hkp server keyserver.ubuntu.com gpg: key E89713C4: public key "Launchpad Peng Huang's PPA" imported gpg: Total number processed: 1 gpg: imported: 1 (RSA: 1)
