每次我尝试执行软件更新时，软件管理器都会出现此错误：
W:GPG error: http://download.virtualbox.org/virtualbox/debian xenial InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY A2F683C52980AECF, W:The repository 'http://download.virtualbox.org/virtualbox/debian xenial InRelease' is not signed., W:Data from such a repository can't be authenticated and is therefore potentially dangerous to use., W:See apt-secure(8) manpage for repository creation and user configuration details., W:There is no public key available for the following key IDs:
A2F683C52980AECF , W:The repository 'http://ppa.launchpad.net/blackmage/f.lux/ubuntu xenial Release' does not have a Release file., W:Data from such a repository can't be authenticated and is therefore potentially dangerous to use., W:See apt-secure(8) manpage for repository creation and user configuration details., W:The repository 'http://ppa.launchpad.net/gezakovacs/ppa/ubuntu xenial Release' does not have a Release file., W:Data from such a repository can't be authenticated and is therefore potentially dangerous to use., W:See apt-secure(8) manpage for repository creation and user configuration details., W:The repository 'http://ppa.launchpad.net/zeal-developers/ppa/ubuntu xenial Release' does not have a Release file., W:Data from such a repository can't be authenticated and is therefore potentially dangerous to use., W:See apt-secure(8) manpage for repository creation and user configuration details., W:http://deb.playonlinux.com/dists/trusty/InRelease: Signature by key 74F7358425EEB6176094C884E0F72778C4676186 uses weak digest algorithm (SHA1), W:http://liveusb.info/multisystem/depot/dists/all/Release.gpg: Signature by key 32027DE3D67157C45E69C0AE4E940D7FDD7FB8CC uses weak digest algorithm (SHA1), W:http://vagrant-deb.linestarve.com/dists/any/InRelease: Signature by key AD319E0F7CFFA38B4D9F6E55CE3F3DE92099F7A4 uses weak digest algorithm (SHA1), E:Failed to fetch http://ppa.launchpad.net/blackmage/f.lux/ubuntu/dists/xenial/main/source/Sources 404 Not Found, E:Failed to fetch http://ppa.launchpad.net/blackmage/f.lux/ubuntu/dists/xenial/main/binary-i386/Packages 404 Not Found, E:Failed to fetch http://ppa.launchpad.net/gezakovacs/ppa/ubuntu/dists/xenial/main/binary-i386/Packages 404 Not Found, E:Failed to fetch http://ppa.launchpad.net/zeal-developers/ppa/ubuntu/dists/xenial/main/source/Sources 404 Not Found, E:Failed to fetch http://ppa.launchpad.net/zeal-developers/ppa/ubuntu/dists/xenial/main/binary-i386/Packages 404 Not Found, E:Some index files failed to download. They have been ignored, or old ones used instead.
以下是我尝试编辑我拥有的存储库时显示的一些屏幕截图：
我不确定如何修复这个问题。
答案1
在命令行中输入此内容：
wget -q http://download.virtualbox.org/virtualbox/debian/oracle_vbox_2016.asc -O- | sudo apt-key add -
答案2
您需要删除升级前遗留的旧密钥。请执行以下操作：
sudo apt-key list
找到有问题的密钥（“virtualbox”附近，“pub”之后，xxx/KEYHERE）并执行以下操作：
sudo apt-key del KEYHERE
然后转到https://www.virtualbox.org/wiki/Linux_Downloads并按照“基于 Debian 的 Linux 发行版”中的说明进行操作
答案3
显然，您之前没有删除外部存储库就进行了系统升级。解决该问题最简单的方法是删除所有外部存储库并删除所有相关公钥。完成此操作后，更新存储库（sudo apt-get update）并检查现在是否已修复所有问题... 当不再出现错误时，您可以添加新的外部存储库，但请仔细检查这些存储库是否“与 Xenial 匹配”...
根据您添加的存储库，更新存储库时仍可能会出现“弱签名”警告 - 但您可以忽略它，因为它只是一条信息消息。
gpg: Signature by key ... uses weak digest algorithm (SHA1)
答案4
我在尝试安装docker时遇到了这个问题。指令建议运行lsb_release -cs并返回serena，但它应该xenial
这样我手动打开文件/etc/apt/sources.list.d/additional-repositories.list并进行了更改：serena->xenial在下一个字符串中：
deb [arch=amd64] https://download.docker.com/linux/ubuntu serena stable
问题已经消失