find 命令可以根据文件的创建时间和访问时间来查找相应的文件，分别可以用 -ctime 和 -atime 选项。
帮助文档给出了如下的解释
-atime n
File was last accessed less than, more than or exactly n*24 hours ago. When find figures out how many 24-hour periods ago the file was last accessed, any fractional
part is ignored, so to match -atime +1, a file has to have been accessed at least two days ago.
-ctime n
File's status was last changed less than, more than or exactly n*24 hours ago. See the comments for -atime to understand how rounding affects the interpretation of
file status change times.
如何查找一周以前创建的文件？这里一周就是7天。可以用 -ctime 选项，
假设 find 的查找路径是 /tmp
sudo find /tmp -ctime +6
注意这里忽略了当天的部分，所以7天前实际是用 +6 来表示。而 +1 实际上是表示至少两天以前。
那么 -ctime -1 和 -ctime +0 分别表示什么含义呢，这是一个值得思考的问题。
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