这个问题我已经遇到一段时间了。首先，我尝试通过软件更新程序更新我的软件。除了 R（开源统计软件）软件包之外，我成功更新了所有软件包。我收到以下错误消息，指出
这需要从未经认证的来源安装软件包。
然后我尝试通过终端更新软件包：
sudo apt-get update
它不起作用。
Hit:2 http://ppa.launchpad.net/alexlarsson/flatpak/ubuntu xenial InRelease
Ign:3 http://dell.archive.canonical.com/updates xenial-dell-service InRelease
Hit:4 http://archive.ubuntu.com/ubuntu xenial-updates InRelease
Hit:5 http://dl.google.com/linux/chrome/deb stable InRelease
Ign:6 http://dell.archive.canonical.com/updates xenial-dell-turis-vegas-mlk-kbl InRelease
Hit:7 http://archive.ubuntu.com/ubuntu xenial-backports InRelease
Hit:8 http://ppa.launchpad.net/codeblocks-devs/release/ubuntu xenial InRelease
Hit:9 http://archive.canonical.com/ubuntu xenial InRelease
Hit:10 http://dell.archive.canonical.com/updates xenial-dell InRelease
Hit:11 http://dell.archive.canonical.com/updates xenial-dell-service Release
Hit:12 http://security.ubuntu.com/ubuntu xenial-security InRelease
Hit:13 http://ppa.launchpad.net/nathan-renniewaldock/flux/ubuntu xenial InRelease
Hit:14 http://dell.archive.canonical.com/updates xenial-dell-turis-vegas-mlk-kbl Release
Get:15 https://cloud.r-project.org/bin/linux/ubuntu xenial-cran35/ InRelease [3625 B]
Ign:15 https://cloud.r-project.org/bin/linux/ubuntu xenial-cran35/ InRelease
Fetched 3625 B in 0s (4471 B/s)
Reading package lists... Done
W: GPG error: https://cloud.r-project.org/bin/linux/ubuntu xenial-cran35/ InRelease: The following signatures were invalid: KEYEXPIRED 1602869253 KEYEXPIRED 1602869253 KEYEXPIRED 1602869253
W: The repository 'https://cloud.r-project.org/bin/linux/ubuntu xenial-cran35/ InRelease' is not signed.
N: Data from such a repository can't be authenticated and is therefore potentially dangerous to use.
N: See apt-secure(8) manpage for repository creation and user configuration details.```
I looked around the web for an answer and I found out that most likely the key has expired so I checked:
```apt-key list|grep "expired:"```
This is the output I got:
```pub 2048R/E084DAB9 2010-10-19 [expired: 2020-10-16]```
Then I tried to renew the expired key:
```gpg --keyserver keys.gnupg.net --recv E084DAB9```
```gpg: requesting key E084DAB9 from hkp server keys.gnupg.net
?: keys.gnupg.net: Host not found
gpgkeys: HTTP fetch error 7: couldn't connect: Success
gpg: no valid OpenPGP data found.
gpg: Total number processed: 0
gpg: keyserver communications error: keyserver unreachable
gpg: keyserver communications error: public key not found
gpg: keyserver receive failed: public key not found```
Nothing happened, so I tried again with another keyserver:
```gpg --keyserver keyserver.ubuntu.com --recv E084DAB9```
```gpg: requesting key E084DAB9 from hkp server keyserver.ubuntu.com
gpg: /home/mainuser/.gnupg/trustdb.gpg: trustdb created
gpg: key E084DAB9: public key "Totally Legit Signing Key <[email protected]>" imported
gpg: Total number processed: 1
gpg: imported: 1 (RSA: 1)```
Then I tried ```sudo apt-get update``` again, and got the same error from before.
Has anyone had the same problem? I have run out of ideas how to fix the expired key issue.
-----------------------
Update - tried this as well
```gpg --export --armor E084DAB9 | sudo apt-key add - ``` (from askubuntu.com/questions/117015/…), still can't install updates.
Tried ```sudo apt-get install --allow-unauthenticated exiv2``` as well, no difference.