在CentOS 使用yum 安装软件的时候 出现错误no more mirrors to try，导致软件安装失败
清理yum源：yum clean all
更新缓存：yum makecache
更新系统：yum -y update
yum man：
* install package1 [package2] [...]
* update [package1] [package2] [...]
* update-to [package1] [package2] [...]
* update-minimal [package1] [package2] [...]
* check-update
* upgrade [package1] [package2] [...]
* upgrade-to [package1] [package2] [...]
* distribution-synchronization [package1] [package2] [...]
* remove | erase package1 [package2] [...]
* autoremove [package1] [...]
* list [...]
* info [...]
* provides | whatprovides feature1 [feature2] [...]
* clean [ packages | metadata | expire-cache | rpmdb | plugins | all ]
* makecache [fast]
* groups [...]
* search string1 [string2] [...]
* shell [filename]
* resolvedep dep1 [dep2] [...]
(maintained for legacy reasons only - use repoquery or yum provides)
* localinstall rpmfile1 [rpmfile2] [...]
(maintained for legacy reasons only - use install)
* localupdate rpmfile1 [rpmfile2] [...]
(maintained for legacy reasons only - use update)
* reinstall package1 [package2] [...]
* downgrade package1 [package2] [...]
* deplist package1 [package2] [...]
* repolist [all|enabled|disabled]
* repoinfo [all|enabled|disabled]
* repository-packages <enabled-repoid> <install|remove|remove-or-reinstall|remove-or-distribution-synchronization> [package2] [...]
* version [ all | installed | available | group-* | nogroups* | grouplist | groupinfo ]
* history [info|list|packages-list|packages-info|summary|addon-info|redo|undo|rollback|new|sync|stats]
* load-transaction [txfile]
* updateinfo [summary | list | info | remove-pkgs-ts | exclude-updates | exclude-all | check-running-kernel]
* fssnapshot [summary | list | have-space | create | delete]
* fs [filters | refilter | refilter-cleanup | du]
* check