我去更新但出现此错误
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://ppa.launchpad.net/u2t/bleedingedge/ubuntu/dists/trusty/main/source/Sources 404 Not Found
W:Failed to fetch http://ppa.launchpad.net/u2t/bleedingedge/ubuntu/dists/trusty/main/binary-amd64/Packages 404 Not Found
W:Failed to fetch http://ppa.launchpad.net/u2t/bleedingedge/ubuntu/dists/trusty/main/binary-i386/Packages 404 Not Found
E:Some index files failed to download. They have been ignored, or old ones used instead.
来源列表：
# deb cdrom:[Ubuntu 14.04 LTS _Trusty Tahr_ - Release amd64 (20140417)]/ trusty 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 trusty main restricted
deb-src http://archive.ubuntu.com/ubuntu trusty main restricted
## Major bug fix updates produced after the final release of the
## distribution.
deb http://archive.ubuntu.com/ubuntu trusty-updates main restricted
deb-src http://archive.ubuntu.com/ubuntu trusty-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 trusty universe
deb-src http://archive.ubuntu.com/ubuntu trusty universe
deb http://archive.ubuntu.com/ubuntu trusty-updates universe
deb-src http://archive.ubuntu.com/ubuntu trusty-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 trusty multiverse
deb-src http://archive.ubuntu.com/ubuntu trusty multiverse
deb http://archive.ubuntu.com/ubuntu trusty-updates multiverse
deb-src http://archive.ubuntu.com/ubuntu trusty-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 trusty-security main restricted
deb-src http://archive.ubuntu.com/ubuntu trusty-security main restricted
deb http://archive.ubuntu.com/ubuntu trusty-security universe
deb-src http://archive.ubuntu.com/ubuntu trusty-security universe
deb http://archive.ubuntu.com/ubuntu trusty-security multiverse
deb-src http://archive.ubuntu.com/ubuntu trusty-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 trusty partner
deb-src http://archive.canonical.com/ubuntu trusty partner
## This software is not part of Ubuntu, but is offered by third-party
## developers who want to ship their latest software.
deb http://extras.ubuntu.com/ubuntu trusty main
deb-src http://extras.ubuntu.com/ubuntu trusty main
答案1
尝试一下sudo add-apt-repository ppa:u2t/bleedingedge它将添加 ppa 以便它变得可见，然后执行此命令sudo add-apt-repository -r ppa:u2t/bleedingedge以正确删除它然后用输出更新您的问题sudo apt-get update
用这个
wget http://download.opensuse.org/repositories/isv:ownCloud:community/xUbuntu_14.04/Release.key
sudo apt-key add - < Release.key
并报告更改，最后两行下载 GPG 密钥并将其添加到 apt 密钥存储区