file max file nr

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Linux的/proc/sys/fs/file-max决定了当前内核可以打开的最大的文件句柄数。
查看当前的值：

cat /proc/sys/fs/file-max

这个值在kernel的文档里是这样描述的：

The value  in  file-max  denotes  the  maximum number of file handles that theLinux kernel will allocate. When you get a lot of error messages about runningout of  file handles, you might want to raise this limit. The default value is10% of  RAM in kilobytes.  To  change it, just  write the new number  into thefile:

意思是file-max一般为内存大小（KB）的10%来计算，如果使用shell，可以这样计算：

grep -r MemTotal /proc/meminfo | awk '{printf("%d",$2/10)}'

一般我们不需要主动设置这个值，除非这个值确实较小（可能有各种其他原因导致file-max没有设置为内存的10%）
如何查看当前kernel的句柄;

cat /proc/sys/fs/file-nr

file-nr在内核文档里得解释如下：

Historically, the three values in file-nr denoted the number of allocated filehandles,  the number of  allocated but  unused file  handles, and  the maximumnumber of file handles. Linux 2.6 always  reports 0 as the number of free filehandles -- this  is not an error,  it just means that the  number of allocatedfile handles exactly matches the number of used file handles.

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