在ubuntu系统下，利用apt-get install命令安装程序，出现如下问题。
jianliu@ubuntu:~$ sudo apt-get install mysql-server mysql-clientReading package lists... DoneBuilding dependency tree Reading state information... DoneE: Unable to locate package mysql-serverE: Unable to locate package mysql-client
可能愿意与解决方法：
(1) 可能在执行apt -get install 命令前，修改了软件源。
———-所以应该调用apt-get update ,更新源，然后再执行apt-get install命令安装程序包就OK 了。
(2)可能所选的软件源存在问题，需要换一个软件源。
#一开始选用了uestc的软件源：http://ubuntu，出现错误！jianliu@ubuntu:~$ sudo apt-get updateIgn trusty InRelease Hit trusty InRelease Hit trusty Release.gpg Hit trusty ReleaseHit trusty/main Sources Hit trusty/main amd64 Packages Hit trusty/main i386 PackagesIgn trusty/main Translation-en_US Ign trusty/main Translation-en Hit trusty/main amd64 Packages Hit trusty/main i386 PackagesHit trusty/main Translation-en Err http://ubuntu. trusty InRelease Err http://ubuntu. trusty-updates InRelease Err http://ubuntu. trusty-backports InReleaseErr http://ubuntu. trusty-security InReleaseErr http://ubuntu. trusty Release.gpg Unable to connect to ubuntu.:http:Err http://ubuntu. trusty-updates Release.gpgUnable to connect to ubuntu.:http:Err http://ubuntu. trusty-backports Release.gpgUnable to connect to ubuntu.:http:Err http://ubuntu. trusty-security Release.gpgUnable to connect to ubuntu.:http:Reading package lists... DoneW: Failed to fetch http://ubuntu./ubuntu/dists/trusty/InRelease W: Failed to fetch http://ubuntu./ubuntu/dists/trusty-updates/InRelease W: Failed to fetch http://ubuntu./ubuntu/dists/trusty-backports/InRelease W: Failed to fetch http://ubuntu./ubuntu/dists/trusty-security/InRelease W: Failed to fetch http://ubuntu./ubuntu/dists/trusty/Release.gpg Unable to connect to ubuntu.:http:W: Failed to fetch http://ubuntu./ubuntu/dists/trusty-updates/Release.gpg Unable to connect to ubuntu.:http:W: Failed to fetch http://ubuntu./ubuntu/dists/trusty-backports/Release.gpg Unable to connect to ubuntu.:http:W: Failed to fetch http://ubuntu./ubuntu/dists/trusty-security/Release.gpg Unable to connect to ubuntu.:http:W: Some index files failed to download. They have been ignored, or old ones used instead.
#后面换成cn99的软件源：/ubuntu,一切正常！jianliu@ubuntu:~$ sudo apt-get updateIgn trusty InReleaseHit trusty-updates InRelease Hit trusty-backports InReleaseHit trusty-security InRelease Hit trusty Release.gpg Hit trusty-updates/main SourcesHit trusty-updates/restricted Sources Hit trusty-updates/universe Sources Hit trusty-updates/multiverse Sources Hit trusty-updates/main amd64 PackagesIgn trusty InRelease Hit trusty-updates/restricted amd64 Packages Hit trusty-updates/universe amd64 PackagesHit trusty InRelease Hit trusty-updates/multiverse amd64 PackagesHit trusty-updates/main i386 Packages Hit trusty-updates/restricted i386 Packages Hit trusty-updates/universe i386 PackagesHit trusty Release.gpg Hit trusty-updates/multiverse i386 Packages Hit trusty-updates/main Translation-en Hit trusty-updates/multiverse Translation-en Hit trusty-updates/restricted Translation-en Hit trusty Release Hit trusty-updates/universe Translation-enHit trusty-backports/main Sources Hit trusty-backports/restricted Sources Hit trusty-backports/universe Sources Hit trusty-backports/multiverse SourcesHit trusty/main amd64 PackagesHit trusty-backports/main amd64 PackagesHit trusty/main Sources Hit trusty-backports/restricted amd64 PackagesHit trusty-backports/universe amd64 Packages Hit trusty-backports/multiverse amd64 PackagesHit trusty-backports/main i386 Packages Hit trusty-backports/restricted i386 Packages Hit trusty-backports/universe i386 Packages Hit trusty/main amd64 Packages Hit trusty-backports/multiverse i386 Packages Hit trusty-backports/main Translation-enHit trusty-backports/multiverse Translation-enHit trusty-backports/restricted Translation-enHit trusty/main i386 PackagesHit trusty-backports/universe Translation-enHit trusty-security/main SourcesHit trusty/main i386 PackagesHit trusty-security/restricted Sources Hit trusty-security/universe SourcesHit trusty-security/multiverse Sources Hit trusty-security/main amd64 Packages Hit trusty-security/restricted amd64 PackagesHit trusty-security/universe amd64 Packages Hit trusty-security/multiverse amd64 PackagesHit trusty-security/main i386 Packages Hit trusty-security/restricted i386 PackagesHit trusty-security/universe i386 PackagesHit trusty-security/multiverse i386 PackagesHit trusty-security/main Translation-enHit trusty-security/multiverse Translation-enHit trusty/main Translation-enHit trusty-security/restricted Translation-enHit trusty-security/universe Translation-enHit trusty ReleaseHit trusty/main Sources Hit trusty/restricted SourcesHit trusty/universe SourcesHit trusty/multiverse SourcesHit trusty/main amd64 PackagesHit trusty/restricted amd64 PackagesHit trusty/universe amd64 PackagesHit trusty/multiverse amd64 PackagesHit trusty/main i386 PackagesHit trusty/restricted i386 PackagesHit trusty/universe i386 PackagesHit trusty/multiverse i386 PackagesHit trusty/main Translation-enHit trusty/multiverse Translation-enHit trusty/restricted Translation-enHit trusty/universe Translation-enIgn trusty/main Translation-en_USIgn trusty/main Translation-en_USIgn trusty/multiverse Translation-en_USIgn trusty/restricted Translation-en_USIgn trusty/universe Translation-en_USIgn trusty/main Translation-enReading package lists... Done
软件源的设置
【system setting】——>【software & Updates】——>【Ubuntu Software】—>[Download from ]
————-默认情况下，选择的美国的软件源，速度很慢！
————--建议选用高校和大公司的软件源。这样apt-get install 安装程序包时速度比较快！
