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
yum clean headers #清理/var/cache/yum的headers
yum clean packages #清理/var/cache/yum下的软件包
yum clean metadata
...
yum clean all #全部清除
Linux释放内存
释放网页缓存(To free pagecache):
sync; echo 1 > /proc/sys/vm/drop_caches
释放目录项和索引(To free dentries and inodes):
sync; echo 2 > /proc/sys/vm/drop_caches
释放网页缓存，目录项和索引（To free pagecache, dentries and inodes）:
sync; echo 3 > /proc/sys/vm/drop_caches
下面是我实际的数据。
[root@localhost ~]# free -m #查看内存
total used free shared buff/cache available
Mem: 481 224 120 1 136 202
Swap: 1023 283 740
[root@localhost ~]# sync; echo 3 > /proc/sys/vm/drop_caches
[root@localhost ~]# free -m #从120到186，释放了66m的内存
total used free shared buff/cache available
Mem: 481 209 186 1 85 222
Swap: 1023 283 740
