在更新 gcc版本的时候
需要用到这个指令：
sudo add-apt-repository ppa:ubuntu-toolchain-r/test然而它报了下面这个错误：
gpg: requesting key BA9EF27F from hkp server keyserver.ubuntu.com
gpg: keyserver timed out
gpg: keyserver receive failed: keyserver error实际上再次运行就可以了。
看到这样的结果就成功了
gpg: requesting key BA9EF27F from hkp server keyserver.ubuntu.com
gpg: key BA9EF27F: public key "Launchpad Toolchain builds" imported
gpg: key BA9EF27F: public key "Totally Legit Signing Key <mallory@example.org>" imported
gpg: Total number processed: 2
gpg: imported: 2 (RSA: 2)
