手上的赚钱宝二代（ws1508）尝试刷入了【唯一一个支持nand flash的版本】，这版固件是基于debian10/buster，内核3.10，不论是debian版本还是内核都比较老。

刷入系统，启动成功以后，根据帖子内容进行了简单的基础配置，然后操作apt update，很快就出现了错误提示。

Err:4 http://mirrors.ustc.edu.cn/debian buster-backports InRelease
  The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 0E98404D386FA1D9 NO_PUBKEY 6ED0E7B82643E131
Reading package lists... Done
W: GPG error: http://mirrors.ustc.edu.cn/debian buster-backports InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 0E98404D386FA1D9 NO_PUBKEY 6ED0E7B82643E131
E: The repository 'http://mirrors.ustc.edu.cn/debian buster-backports InRelease' is not signed.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.

大致意思就是有俩公钥不可用，提示中给出了俩有问题公钥的编号。那公钥编号都有了，根据编号重新导入就行。

apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv 0E98404D386FA1D9

导入成功以后提示

root@WS1508:~# apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv 0E98404D386FA1D9
Executing: /tmp/apt-key-gpghome.g8lGjyqWFg/gpg.1.sh --keyserver hkp://keyserver.ubuntu.com:80 --recv 0E98404D386FA1D9
gpg: key 73A4F27B8DD47936: public key "Debian Archive Automatic Signing Key (11/bullseye) <ftpmaster@debian.org>" imported
gpg: Total number processed: 1
gpg:               imported: 1

重新执行apt update，问题解决。