顶部面板上有一个红色三角形，上面写着
The update information is outdated. This may be caused by network problems or by a repository that is no longer available. Please update manually by selecting show updates from the indicator menu and watching for any failing repositories.
我的 Ubuntu 是最新的。打开笔记本电脑后需要一段时间才能显示，而且即使 Ubuntu 是最新的，它总是会返回。
输出sudo apt-get upgrade：
Reading package lists... Done
Building dependency tree
Reading state information... Done
Calculating upgrade... Done
The following packages were automatically installed and are no longer required:
libbit-vector-perl libcarp-clan-perl libclass-method-modifiers-perl
libdata-random-perl libdate-calc-perl libdate-calc-xs-perl libgd-perl
libgnome2-gconf-perl libmouse-perl libnet-dropbox-api-perl
linux-headers-3.13.0-32 linux-headers-3.13.0-32-generic
linux-image-3.13.0-32-generic linux-image-extra-3.13.0-32-generic
Use 'apt-get autoremove' to remove them.
0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
以下是输出sudo apt-get update：
Ign http://ppa.launchpad.net trusty InRelease
Ign http://ppa.launchpad.net trusty InRelease
Ign http://ppa.launchpad.net trusty InRelease
Ign http://ppa.launchpad.net trusty InRelease
Ign http://ppa.launchpad.net trusty InRelease
Hit http://ppa.launchpad.net trusty Release.gpg
Hit http://ppa.launchpad.net trusty Release.gpg
Hit http://ppa.launchpad.net trusty Release.gpg
Hit http://ppa.launchpad.net trusty Release.gpg
Hit http://ppa.launchpad.net trusty Release.gpg
Hit http://ppa.launchpad.net trusty Release
Hit http://ppa.launchpad.net trusty Release
Hit http://ppa.launchpad.net trusty Release
Ign http://ie.archive.ubuntu.com trusty InRelease
Ign http://old-releases.ubuntu.com raring InRelease
Hit http://ppa.launchpad.net trusty Release
Ign http://ie.archive.ubuntu.com trusty-updates InRelease
Hit http://old-releases.ubuntu.com raring Release.gpg
Ign http://ie.archive.ubuntu.com trusty-backports InRelease
Hit http://ppa.launchpad.net trusty Release
Hit http://ie.archive.ubuntu.com trusty Release.gpg
Hit http://old-releases.ubuntu.com raring Release
Hit http://ppa.launchpad.net trusty/main amd64 Packages
Get:1 http://ie.archive.ubuntu.com trusty-updates Release.gpg [933 B]
Hit http://ppa.launchpad.net trusty/main i386 Packages
Hit http://old-releases.ubuntu.com raring/main amd64 Packages
Hit http://ie.archive.ubuntu.com trusty-backports Release.gpg
Hit http://ppa.launchpad.net trusty/main Translation-en
Hit http://ie.archive.ubuntu.com trusty Release
Hit http://old-releases.ubuntu.com raring/restricted amd64 Packages
Get:2 http://ie.archive.ubuntu.com trusty-updates Release [62.0 kB]
Hit http://old-releases.ubuntu.com raring/universe amd64 Packages
Hit http://old-releases.ubuntu.com raring/multiverse amd64 Packages
Hit http://ppa.launchpad.net trusty/main amd64 Packages
Hit http://old-releases.ubuntu.com raring/main i386 Packages
Hit http://ppa.launchpad.net trusty/main i386 Packages
Hit http://old-releases.ubuntu.com raring/restricted i386 Packages
Hit http://old-releases.ubuntu.com raring/universe i386 Packages
Hit http://ie.archive.ubuntu.com trusty-backports Release
Hit http://ie.archive.ubuntu.com trusty/main Sources
Hit http://old-releases.ubuntu.com raring/multiverse i386 Packages
Hit http://ppa.launchpad.net trusty/main amd64 Packages
Hit http://ie.archive.ubuntu.com trusty/restricted Sources
Hit http://ppa.launchpad.net trusty/main i386 Packages
Hit http://ie.archive.ubuntu.com trusty/universe Sources
Hit http://old-releases.ubuntu.com raring/main Translation-en
Hit http://ppa.launchpad.net trusty/main Translation-en
Hit http://ie.archive.ubuntu.com trusty/multiverse Sources
Hit http://ie.archive.ubuntu.com trusty/main amd64 Packages
Hit http://ppa.launchpad.net trusty/main amd64 Packages
Hit http://ie.archive.ubuntu.com trusty/restricted amd64 Packages
Hit http://old-releases.ubuntu.com raring/multiverse Translation-en
Hit http://ppa.launchpad.net trusty/main i386 Packages
Hit http://ie.archive.ubuntu.com trusty/universe amd64 Packages
Hit http://ppa.launchpad.net trusty/main Translation-en
Hit http://ie.archive.ubuntu.com trusty/multiverse amd64 Packages
Hit http://old-releases.ubuntu.com raring/restricted Translation-en
Hit http://ppa.launchpad.net trusty/main amd64 Packages
Hit http://ie.archive.ubuntu.com trusty/main i386 Packages
Hit http://ppa.launchpad.net trusty/main i386 Packages
Hit http://ie.archive.ubuntu.com trusty/restricted i386 Packages
Hit http://old-releases.ubuntu.com raring/universe Translation-en
Hit http://ie.archive.ubuntu.com trusty/universe i386 Packages
Hit http://ie.archive.ubuntu.com trusty/multiverse i386 Packages
Hit http://ie.archive.ubuntu.com trusty/main Translation-en
Hit http://ie.archive.ubuntu.com trusty/multiverse Translation-en
Hit http://ie.archive.ubuntu.com trusty/restricted Translation-en
Hit http://ie.archive.ubuntu.com trusty/universe Translation-en
Get:3 http://ie.archive.ubuntu.com trusty-updates/main Sources [152 kB]
Ign http://old-releases.ubuntu.com raring/main Translation-en_IE
Ign http://ppa.launchpad.net trusty/main Translation-en_IE
Get:4 http://ie.archive.ubuntu.com trusty-updates/restricted Sources [2,061 B]
Ign http://old-releases.ubuntu.com raring/multiverse Translation-en_IE
Ign http://ppa.launchpad.net trusty/main Translation-en
Get:5 http://ie.archive.ubuntu.com trusty-updates/universe Sources [96.5 kB]
Ign http://old-releases.ubuntu.com raring/restricted Translation-en_IE
Ign http://ppa.launchpad.net trusty/main Translation-en_IE
Ign http://old-releases.ubuntu.com raring/universe Translation-en_IE
Ign http://ppa.launchpad.net trusty/main Translation-en
Get:6 http://ie.archive.ubuntu.com trusty-updates/multiverse Sources [3,543 B]
Get:7 http://ie.archive.ubuntu.com trusty-updates/main amd64 Packages [392 kB]
Get:8 http://ie.archive.ubuntu.com trusty-updates/restricted amd64 Packages [8,875 B]
Get:9 http://ie.archive.ubuntu.com trusty-updates/universe amd64 Packages [236 kB]
Get:10 http://ie.archive.ubuntu.com trusty-updates/multiverse amd64 Packages [9,370 B]
Get:11 http://ie.archive.ubuntu.com trusty-updates/main i386 Packages [384 kB]
Get:12 http://ie.archive.ubuntu.com trusty-updates/restricted i386 Packages [8,846 B]
Get:13 http://ie.archive.ubuntu.com trusty-updates/universe i386 Packages [237 kB]
Get:14 http://ie.archive.ubuntu.com trusty-updates/multiverse i386 Packages [9,553 B]
Hit http://ie.archive.ubuntu.com trusty-updates/main Translation-en
Hit http://ie.archive.ubuntu.com trusty-updates/multiverse Translation-en
Hit http://ie.archive.ubuntu.com trusty-updates/restricted Translation-en
Hit http://ie.archive.ubuntu.com trusty-updates/universe Translation-en
Hit http://ie.archive.ubuntu.com trusty-backports/main Sources
Hit http://ie.archive.ubuntu.com trusty-backports/restricted Sources
Hit http://ie.archive.ubuntu.com trusty-backports/universe Sources
Hit http://ie.archive.ubuntu.com trusty-backports/multiverse Sources
Hit http://ie.archive.ubuntu.com trusty-backports/main amd64 Packages
Hit http://ie.archive.ubuntu.com trusty-backports/restricted amd64 Packages
Hit http://ie.archive.ubuntu.com trusty-backports/universe amd64 Packages
Hit http://ie.archive.ubuntu.com trusty-backports/multiverse amd64 Packages
Hit http://ie.archive.ubuntu.com trusty-backports/main i386 Packages
Hit http://ie.archive.ubuntu.com trusty-backports/restricted i386 Packages
Hit http://ie.archive.ubuntu.com trusty-backports/universe i386 Packages
Hit http://ie.archive.ubuntu.com trusty-backports/multiverse i386 Packages
Hit http://ie.archive.ubuntu.com trusty-backports/main Translation-en
Hit http://ie.archive.ubuntu.com trusty-backports/multiverse Translation-en
Hit http://ie.archive.ubuntu.com trusty-backports/restricted Translation-en
Hit http://ie.archive.ubuntu.com trusty-backports/universe Translation-en
Ign http://ie.archive.ubuntu.com trusty/main Translation-en_IE
Ign http://ie.archive.ubuntu.com trusty/multiverse Translation-en_IE
Ign http://ie.archive.ubuntu.com trusty/restricted Translation-en_IE
Ign http://ie.archive.ubuntu.com trusty/universe Translation-en_IE
Err http://security.ubuntu.com trusty-security InRelease
Err http://security.ubuntu.com trusty-security Release.gpg
Could not resolve 'security.ubuntu.com'
Err http://dl.google.com stable InRelease
Err http://dl.google.com stable Release.gpg
Could not resolve 'dl.google.com'
Err http://linux.dropbox.com trusty InRelease
Err http://linux.dropbox.com trusty Release.gpg
Could not resolve 'linux.dropbox.com'
Err http://extras.ubuntu.com trusty InRelease
Err http://extras.ubuntu.com trusty Release.gpg
Could not resolve 'extras.ubuntu.com'
Fetched 1,602 kB in 40s (39.9 kB/s)
Reading package lists... Done
W: Failed to fetch http://security.ubuntu.com/ubuntu/dists/trusty-security/InRelease
W: Failed to fetch http://extras.ubuntu.com/ubuntu/dists/trusty/InRelease
W: Failed to fetch http://linux.dropbox.com/ubuntu/dists/trusty/InRelease
W: Failed to fetch http://dl.google.com/linux/chrome/deb/dists/stable/InRelease
W: Failed to fetch http://security.ubuntu.com/ubuntu/dists/trusty-security/Release.gpg Could not resolve 'security.ubuntu.com'
W: Failed to fetch http://dl.google.com/linux/chrome/deb/dists/stable/Release.gpg Could not resolve 'dl.google.com'
W: Failed to fetch http://linux.dropbox.com/ubuntu/dists/trusty/Release.gpg Could not resolve 'linux.dropbox.com'
W: Failed to fetch http://extras.ubuntu.com/ubuntu/dists/trusty/Release.gpg Could not resolve 'extras.ubuntu.com'
W: Some index files failed to download. They have been ignored, or old ones used instead.
答案1
红色标记表示更新问题。第二条日志显示获取存储库更新时出现问题（“某些索引文件下载失败”，尤其是“无法解决”）。
可能的原因和解决方案
（从最有可能到最不可能。）
姓名查找问题
当前 DNS 服务器发生故障
解决方案：使用其他服务器（例如 Google 的 DNS 服务器：IP 8.8.4.4 和 8.8.8.8）
Hosts 文件已修改
解决方案：检查文件
/etc/hosts中是否包含“google”、“dropbox”、“ubuntu”的行。如果包含，请清除这些行（或用初始干净版本替换文件）
网络连接中断
互联网服务提供商
解决方案：尝试使用其他 ISP
网络适配器性能不稳定
解决方案：尝试使用另一个适配器（从有线网络切换到无线网络或反之亦然；插入另一个适配器，例如 USB 适配器）
恶意软件感染
解决方案：执行恶意软件检查，最好是离线检查。
大多数情况下是 DNS 服务器问题。