我正在试验 VPN，所以我想安装 pptpd。
john@desktop:~$ sudo apt-get install pptpd
[sudo] password for john:
<snip>
The following extra packages will be installed:
bcrelay
The following NEW packages will be installed:
bcrelay pptpd
0 upgraded, 2 newly installed, 0 to remove and 11 not upgraded.
Need to get 90.5 kB of archives.
After this operation, 442 kB of additional disk space will be used.
Do you want to continue [Y/n]? y
一切都运行良好，直到我到达这里：
WARNING: The following packages cannot be authenticated!
bcrelay pptpd
Install these …我经常遇到这个问题，总是不得不谷歌寻找答案。有没有人有永久修复 BADSIG 错误的方法apt-get？
W：GPG 错误：http : //download.virtualbox.org lucid 发布：以下签名无效：BADSIG 54422A4B98AB5139 Oracle Corporation（VirtualBox 存档签名密钥）
我刚刚收到一些关于 GPG 密钥的奇怪错误。即我刚刚添加ppa:ubuntu-toolchain-r/test并想要更新，之后我得到了这个：
W: GPG error: http://extras.ubuntu.com trusty Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 16126D3A3E5C1192
W: GPG error: http://archive.canonical.com trusty Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 40976EAF437D05B5 NO_PUBKEY 3B4FE6ACC0B21F32
W: GPG error: http://qgis.org trusty InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 030561BEDD45F6C3
W: GPG error: http://dl.google.com stable Release: The following signatures couldn't …