GPG Signature Validation Error

The following method is I combined with my own computer problems, and reference http://quickbest.com.cn/discuz/thread-29988-1-1.html, I hope you learn together, remove windows!!

Problem Description:
W:GPG Signature validation error: http://www.debian-multimedia.org SID Release: Because there is no public key, the following signature cannot be verified: No_pubkey 07dc563d1f41b907

The workaround can be resolved as follows:
To add a public key command:
$ gpg--keyserver subkeys.pgp.net--recv 4f6c1e86
$ gpg--export--armor 4f6c1e86 | sudo apt-key add-

For error hints:
Reference:

Reading Package List ... Complete
W:GPG Signature validation error: http://deb.opera.com unstable Release: Because there is no public key, the following signature cannot be verified: No_pubkey 033431536a423791
W: You may need to run Apt-get update to resolve these issues



You need to replace the "4f6c1e86" in the two lines of the above command with the last 8 bits of the string after "No_pubkey", namely:
$ gpg--keyserver subkeys.pgp.net--recv 6a423791
$ gpg--export--armor 6a423791 | sudo apt-key add-


Summary: In addition, my update also has a problem with the software source, so use the following two command lines:
sudo cp/etc/apt/sources.list/etc/apt/sources.list_backup
sudo gedit/etc/apt/sources.list
Open the update source file, look inside to copy the new address, you can find the latest Wiki official website. But there is still no solution.
The final solution is to enter system/System Management/software source/download from
Go to this drop-down list, select Other, and then select the fastest address. Problem solving!!!!!!!!

Note: The red part of the font is the reference content.

Original address: http://forum.ubuntu.org.cn/viewtopic.php?p=938139

GPG Signature Validation Error