Solve the Problem of gpgerror caused by the lack of public key during apt-getupdate In debian.

In debian, if the public key is missing during apt-getupdate, The gpgerror-Linux Release Technology-Debian information is displayed. See the following for details. Sometimes, when an unofficial source is added, a gpg error message without a public key is displayed, indicating that there may be a backdoor program, which is annoying for frequent update.

The solution is to import the public key and use the following statement:

Gpg -- keyserver wwwkeys.eu.pgp.net -- recv-keys indicates the public key that is missing.
Gpg -- armor -- export public key string | apt-key add-

For example, debian-multimedia.org and ftp://debian.ustc.edu.cn two sources:

Error:
W: GPG error: http://www.debian-multimedia.org testing Release: The following signature cannot be verified because there is no public key: NO_PUBKEY 07DC563D1F41B907
W: GPG error: ftp://debian.ustc.edu.cn sid Release: The following signature cannot be verified because there is no public key: NO_PUBKEY D4F3554EF747D1A0

Solution:

Input:
# Gpg -- keyserver wwwkeys.eu.pgp.net -- recv-keys 07DC563D1F41B907

Output:
Gpg: requesting key 1F41B907 from hkp server wwwkeys.eu.pgp.net
Gpg: key 1F41B907: "Christian Marillat "1 new signature
Gpg: key 1F41B907: "Christian Marillat "1 new subkey
Gpg: no ultimately trusted keys found
Gpg: Total number processed: 1
Gpg: new subkeys: 1
Gpg: new signatures: 1

Input:
# Gpg -- armor -- export 1F41B907 | apt-key add-

Output:
OK

Input:
# Gpg -- keyserver wwwkeys.eu.pgp.net -- recv-keys D4F3554EF747D1A0

Output:
Gpg: requesting key F747D1A0 from hkp server wwwkeys.eu.pgp.net
Gpg: key F747D1A0: public key "Debian at USTC "Imported
Gpg: no ultimately trusted keys found
Gpg: Total number processed: 1
Gpg: imported: 1

Input:
# Gpg -- armor -- export F747D1A0 | apt-key add-

Output:
OK

In this way, there will be no gpg error after apt-get update.