atime ctime mtime

最新推荐文章于 2024-12-28 15:06:40 发布

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最新推荐文章于 2024-12-28 15:06:40 发布

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本文链接：https://blog.youkuaiyun.com/yifeng_1118/article/details/17148539

本文探讨了Linux系统中文件访问时间（atime）的更新机制，并对比了不同内核版本下atime更新的行为差异。从Ubuntu和GXLINUX系统的实际测试出发，指出了atime更新对性能的影响，并介绍了2.6.30版本引入的relatime特性如何改善这一状况。

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stat 文件可以看文件的修改时间。

UNBUNTU:

修改文件内容，这个三个都会变。

chmod 等改ctime

touch 改所有。

当修改内容后，第一次访问的时候能够修改atime,后面继续访问，atime不会修改（有问题！）

uname -r :3.2.0

GXLINUX

也不正常，atime也不能按照访问时间同步！

uname -r :2.6.26-8-co-0.7.7

开发板2.6.22是正常的。

答案可以参见

atime updates are by far the biggest IO performance deficiency that Linux has today. Getting rid of atime updates would give us more everyday Linux performance than all the pagecache speedups of the past 10 years, _combined_.

As of 2.6.30 (9 June 2009), Linux defaults to relatime,^[3] so that it will not update atime on all file reads. The behavior offers sufficient performance for most purposes and should not break any significant applications. Extended discussion of filesystem performance preceded the decision.^[4] Indeed, relatime by default was the first patch Linux applied following the 2.6.29 release. In initial patchesrelatime only updated atime if atime < mtime or atime < ctime;

http://blog.youkuaiyun.com/cjf_iceking/article/details/11988525