这些是我尝试了 Internet 上提到的几个修复后仍然存在的签名错误
W: GPG error: http://deb.opera.com stable InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 517590D9A8492E35
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://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://linux.dropbox.com trusty Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY FC918B335044912E
W: GPG error: http://dl.google.com stable Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY A040830F7FAC5991
W: GPG error: http://dl.google.com stable Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY A040830F7FAC5991
W: GPG error: http://archive.ubuntu.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: https://private-ppa.launchpad.net raring Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY E131728675254D99
W: GPG error: http://archive.ubuntu.com trusty-updates 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://archive.ubuntu.com trusty-backports Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 40976EAF437D05B5 NO_PUBKEY 3B4FE6ACC0B21F32
W: GPG error: https://private-ppa.launchpad.net trusty Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY E131728675254D99
W: GPG error: http://archive.ubuntu.com trusty-security 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://ppa.launchpad.net trusty Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 0CC3AFF5CEDF0F40
W: GPG error: http://ppa.launchpad.net trusty Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 32B18A1260D8DA0B
我一直在寻找解决方案，但没有任何效果，请提出一些可以解决这些错误的建议。
我已经尝试过的：
- y-ppa-经理
- 手动删除列表并重新生成它。
所以请不要为这些方法标记重复并提出其他建议。
您的 apt 密钥或添加/更改存储库或其他内容出了点问题……我不知道是什么
但这里有一些针对您的症状的创可贴解决方案：
要仅添加缺少的键，此命令应该有效（用您实际缺少的键替换“2EA8 ...”字符串）
--keyserver keys.gnupg.net如果没有在 ubuntu 上，可以尝试[参见https://askubuntu.com/a/141088/129271 ]
看起来你没有正确添加一些 PPA，根据 Ubuntu 的说明，它应该自己“获取 PPA 的密钥”。这是来自https://help.ubuntu.com/community/Repositories/Ubuntu的终端说明
如果您的软件源有问题，这应该将它们恢复为“默认值”。我会先备份所有内容
/ect/apt/sources.list，/ect/apt/sources.list.d/以防万一。不知道你的 Ubuntu 版本是什么，我不确定“默认值”应该是什么，或者你是否添加了额外的 PPA 或其他来源。运行lsb_release -a应该会告诉你你的版本和“代号”备份 sources.list 文件
只需将它们复制到某处的备份文件夹，这应该有效：
sudo mv /etc/apt/sources.list /etc/apt/sources.list.oldsudo mv /etc/apt/sources.list.d /etc/apt/sources.list.d.old恢复默认的 Ubuntu
sources.list对于 Ubuntu，如果你这样做，它应该生成一个新的新
sources.list文件删除旧文件（
sudo rm /etc/apt/sources.list但sudo rm -R /etc/apt/sources.list.d先备份）。然后执行以下任一操作：
运行软件源（
sudo software-properties-gtk或sudo software-sources）选择/勾选一些存储库，选择一个服务器并更新。使用您的版本和国家（选择本地镜像）在http://repogen.simplylinux.ch/生成一个新的，然后使用
gksudo gedit /etc/apt/sources.list或在终端中将其复制并粘贴到您的新 sources.list 中sudo nano /etc/apt/sources.list该网站http://repogen.simplylinux.ch/也有很多可选的 PPA，看起来很有用。[礼貌如何恢复默认存储库？]
在知道 apt 不能处理超过 40 个密钥后，我开始从 /etc/apt/trusted.gpg.d 中删除 ppa 和它们的密钥
这样做之后，我更新了 apt-cache，我的问题就解决了。