apt-get couldn't be verified because the public key is not available: NO_PUBKEY XXX

root@ubuntu:/opt/EmbedSky/kernel/x86/linux-3.5# sudo apt-get update
......                                                                                                                                             
Hit http://us.archive.ubuntu.com precise/universe Translation-en                                                                                                                                                       
Fetched 3,105 kB in 31s (99.2 kB/s)                                                                                                                                                                                    
W: GPG error: http://ddebs.ubuntu.com precise Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY C8CAB6595FDFF622
W: GPG error: http://ddebs.ubuntu.com precise-updates Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY C8CAB6595FDFF622

W: GPG error: http://ddebs.ubuntu.com precise-proposed Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY C8CAB6595FDFF622

解决方案：

apt-key adv --recv-keys --keyserver keyserver.ubuntu.com C8CAB6595FDFF622

实际上类似的问题无论Key是什么只需要使用相同的代码替换到相对的Key的位置即可。