刚刚安装了 ubuntu 15.10，但是当我尝试执行操作时sudo apt-get update，出现以下错误：
W: GPG error: http://download.opensuse.org Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 977C43A8BA684223
W: Failed to fetch http://archive.ubuntu.com/ubuntu/dists/wily-updates/main/source/Sources Hash Sum mismatch
W: Failed to fetch http://archive.ubuntu.com/ubuntu/dists/wily-updates/main/binary-amd64/Packages Hash Sum mismatch
W: Failed to fetch http://archive.ubuntu.com/ubuntu/dists/wily-updates/main/binary-i386/Packages Hash Sum mismatch
E: Some index files failed to download. They have been ignored, or old ones used instead.
这是 /etc/apt/sources.list
#deb cdrom:[Ubuntu 15.10 _Wily Werewolf_ - Release amd64 (20151021)]/ wily main restricted
# See http://help.ubuntu.com/community/UpgradeNotes for how to upgrade to
# newer versions of the distribution.
deb http://archive.ubuntu.com/ubuntu/ wily main restricted
deb-src http://archive.ubuntu.com/ubuntu/ wily main restricted
## Major bug fix updates produced after the final release of the
## distribution.
deb http://archive.ubuntu.com/ubuntu/ wily-updates main restricted
deb-src http://archive.ubuntu.com/ubuntu/ wily-updates main restricted
## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
## team. Also, please note that software in universe WILL NOT receive any
## review or updates from the Ubuntu security team.
deb http://archive.ubuntu.com/ubuntu/ wily universe
deb-src http://archive.ubuntu.com/ubuntu/ wily universe
deb http://archive.ubuntu.com/ubuntu/ wily-updates universe
deb-src http://archive.ubuntu.com/ubuntu/ wily-updates universe
## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
## team, and may not be under a free licence. Please satisfy yourself as to
## your rights to use the software. Also, please note that software in
## multiverse WILL NOT receive any review or updates from the Ubuntu
## security team.
deb http://archive.ubuntu.com/ubuntu/ wily multiverse
deb-src http://archive.ubuntu.com/ubuntu/ wily multiverse
deb http://archive.ubuntu.com/ubuntu/ wily-updates multiverse
deb-src http://archive.ubuntu.com/ubuntu/ wily-updates multiverse
## N.B. software from this repository may not have been tested as
## extensively as that contained in the main release, although it includes
## newer versions of some applications which may provide useful features.
## Also, please note that software in backports WILL NOT receive any review
## or updates from the Ubuntu security team.
deb http://archive.ubuntu.com/ubuntu/ wily-backports main restricted universe multiverse
deb-src http://archive.ubuntu.com/ubuntu/ wily-backports main restricted universe multiverse
deb http://security.ubuntu.com/ubuntu wily-security main restricted
deb-src http://security.ubuntu.com/ubuntu wily-security main restricted
deb http://security.ubuntu.com/ubuntu wily-security universe
deb-src http://security.ubuntu.com/ubuntu wily-security universe
deb http://security.ubuntu.com/ubuntu wily-security multiverse
deb-src http://security.ubuntu.com/ubuntu wily-security multiverse
## Uncomment the following two lines to add software from Canonical's
## 'partner' repository.
## This software is not part of Ubuntu, but is offered by Canonical and the
## respective vendors as a service to Ubuntu users.
# deb http://archive.canonical.com/ubuntu wily partner
# deb-src http://archive.canonical.com/ubuntu wily partner
有什么帮助吗？
答案1
您收到的错误信息：
W：GPG 错误：http://download.opensuse.org 发布：由于公钥不可用，无法验证以下签名：NO_PUBKEY 977C43A8BA684223
意味着您必须977C43A8BA684223 先重新下载密钥来添加丢失的密钥：
sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys
然后输入：
sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 977C43A8BA684223
sudo apt-get update
答案2
我相信您缺少 Ubuntu 密钥服务器的密钥。请尝试以下操作：
# sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 977C43A8BA684223