清理yum缓存

清理yum缓存使用yum clean 命令，yum clean 的参数有headers, packages, metadata, dbcache, plugins, expire-cache, rpmdb, all

　　yumcleanheaders#清理/var/cache/yum的headersyumcleanpackages#清理/var/cache/yum下的软件包yumcleanmetadata...1234Linux释放内存

释放网页缓存(To free pagecache):

　　sync;echo1>/proc/sys/vm/drop_caches1

释放目录项和索引(To free dentries and inodes):

　　sync;echo2>/proc/sys/vm/drop_caches1

释放网页缓存，目录项和索引（To free pagecache, dentries and inodes）:

　　sync;echo3>/proc/sys/vm/drop_caches1