環境: Sury packages on debian 9
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						apt update output: An error occurred during the signature verification. The repository is not updated and the previous index files will be used. GPG error: https://packages.sury.org/php stretch InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY B188E2B695BD4743 Failed to fetch https://packages.sury.org/php/dists/stretch/InRelease  The following signatures couldn't be verified because the public key is not available: NO_PUBKEY B188E2B695BD4743 Some index files failed to download. They have been ignored, or old ones used instead.  | 
					
發生原因為 https://packages.sury.org/ 的 apt.gpg 於 18-Mar-2019 更新
解決方法
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						wget -O /etc/apt/trusted.gpg.d/php.gpg https://packages.sury.org/php/apt.gpg  | 
					
再重新執行
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						apt update  | 
					
