GPG error: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY

在嘗試安裝 Foxwiki 時，遇到手動加入 deb 位址時，apt-get 無法正確存取，解決方式如 [1] 的回應所說。
例如 Foswiki 出現的錯誤訊息如下：
W: GPG error: http://fosiki.com stable Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 379393E0AAEE96F6
則輸入的指令是：

gpg --keyserver hkp://keyserver.ubuntu.com:80 --recv 379393E0AAEE96F6
gpg --export --armor 379393E0AAEE96F6 | sudo apt-key add -

系統回應的結果如下：

root@ubuntu:~# gpg --keyserver hkp://keyserver.ubuntu.com:80 --recv 379393E0AAEE96F6
gpg: directory `/root/.gnupg' created
gpg: new configuration file `/root/.gnupg/gpg.conf' created
gpg: WARNING: options in `/root/.gnupg/gpg.conf' are not yet active during this run
gpg: keyring `/root/.gnupg/secring.gpg' created
gpg: keyring `/root/.gnupg/pubring.gpg' created
gpg: requesting key AAEE96F6 from hkp server keyserver.ubuntu.com
gpg: /root/.gnupg/trustdb.gpg: trustdb created
gpg: key AAEE96F6: public key "Fosiki Software Releases (Release signing user) <Releases@fosiki.com>" imported
gpg: no ultimately trusted keys found
gpg: Total number processed: 1
gpg:               imported: 1  (RSA: 1)
root@ubuntu:~# gpg --export --armor 379393E0AAEE96F6 | sudo apt-key add -                                                                                                        OK

參考資料：
1、How do I fix the GPG error “NO_PUBKEY”?