linux系统如何进行Cache空间的清理及调试
Linux下清理内存和Cache方法 /proc/sys/vm/drop_caches
频繁的文件访问会导致系统的Cache使用量大增
$ free -m
total used free shared buffers cached
Mem: 3955 3926 28 0 55 3459
-/+ buffers/cache: 411 3544
Swap: 5726 0 5726
free内存减少到几十兆，系统运行缓慢
运行sync将dirty的内容写回硬盘
$sync
通过修改proc系统的drop_caches清理free的cache
$echo 3 > /proc/sys/vm/drop_caches
drop_caches的详细文档如下：
Writing to this will cause the kernel to drop clean caches, dentries and inodes from memory, causing that memory to become free.
To free pagecache:
* echo 1 > /proc/sys/vm/drop_caches
To free dentries and inodes:
* echo 2 > /proc/sys/vm/drop_caches
To free pagecache, dentries and inodes:
* echo 3 > /proc/sys/vm/drop_caches
As this is a non-destructive operation, and dirty objects are notfreeable, the user should run sync first in order to make sure allcached objects are freed.
This tunable was added in 2.6.16.
修改/etc/sysctl.conf 添加如636f下选项后就不会内存持续增加
vm.dirty_ratio = 1
vm.dirty_background_ratio=1
vm.dirty_writeback_centisecs=2
vm.dirty_expire_centisecs=3
vm.drop_caches=3
vm.swappiness =100
vm.vfs_cache_pressure=163
vm.overcommit_memory=2
vm.lowmem_reserve_ratio=32 32 8
kern.maxvnodes=3
上面的设置比较粗暴，使cache的作用基本无法发挥。需要根据机器的状况进行适当的调节寻找最佳的折衷。
怎么查看linux是lubuntu
1，查看内核版本命令：
cat /proc/version
uname -a
uname -rcat /etc/issue
man uname
2，查看linux版本：抄录如下：
1) 登录到服务器执行 lsb_release -a ，即可列出所有版本信息，例如：
[root@3.5.5Biz-46 ~]# lsb_release -a
LSB Version: 1.3
Distributor ID: RedHatEnterpriseAS
Descrīption: Red Hat Enterprise Linux AS release 4 (Nahant Update 1)
Release: 4
Codename: NahantUpdate1
[root@3.5.5Biz-46 ~]#
这个命令适用于所有的linux，包括Redhat、SuSE、Debian等发行版。
2) 登录到linux执行cat /etc/redhat-release ，例如如下：
[root@3.5.5Biz-46 ~]# cat /etc/redhat-release
Red Hat Enterprise Linux AS release 4 (Nahant Update 1)
[root@3.5.5Biz-46 ~]#
这种方式下可以直接看到具体的版本号，比如 AS4 Update 1
3）登录到linux执行rpm -q redhat-release ，例如如下
[root@3.5.5Biz-46 ~]# rpm -q redhat-release
redhat-release-4AS-2.4
[root@3.5.5Biz-46 ~]#
这种方式下可看到一个所谓的release号，比如上边的例子是2.4
这个release号和实际的版本之间存在一定的对应关系，如下：
redhat-release-3AS-1 -> Redhat Enterprise Linux AS 3
redhat-release-3AS-7.4 -> Redhat Enterprise Linux AS 3 Update 4
redhat-release-4AS-2 -> Redhat Enterprise Linux AS 4
redhat-release-4AS-2.4 -> Redhat Enterprise Linux AS 4 Update 1
redhat-release-4AS-3 -> Redhat Enterprise Linux AS 4 Update 2
redhat-release-4AS-4.1 -> Redhat Enterprise Linux AS 4 Update 3
redhat-release-4AS-5.5 -> Redhat Enterprise Linux AS 4 Update 4
