错误信息:

W: GPG error: http://security.debian.org testing/updates Release: 由于没有公钥,下列签名无法进行验证: NO_PUBKEY 9AA38DCD55BE302B
W: GPG error: ftp://ftp.tw.debian.org testing Release: 由于没有公钥,下列签名无法进行验证: NO_PUBKEY 9AA38DCD55BE302B
W: Duplicate sources.list entry ftp://ftp.tw.debian.org testing/main Packages (/var/lib/apt/lists/ftp.tw.debian.org_debian_dists_testing_main_binary-i386_Packages)
W: Duplicate sources.list entry ftp://ftp.tw.debian.org testing/main Translation-zh_CN (/var/lib/apt/lists/ftp.tw.debian.org_debian_dists_testing_main_i18n_Translation-zh%5fCN)
W: Duplicate sources.list entry http://security.debian.org testing/updates/main Packages (/var/lib/apt/lists/security.debian.org_dists_testing_updates_main_binary-i386_Packages)

解决办法:

su

输入root密码获得权限

apt-get update -o Acquire::Pdiffs=false
apt-get dist-upgrade

再试试apt-get update,问题解决!