/proc/sys/fs/file-max

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 the
linux kernel will allocate. when you get a lot of error messages about running
out of  file handles, you might want to raise this limit. the default value is
10% of  ram in kilobytes.  to  change it, just  write the new number  into the
file:

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 file
handles,  the number of  allocated but  unused file  handles, and  the maximum
number of file handles. linux 2.6 always  reports 0 as the number of free file
handles -- this  is not an error,  it just means that the  number of allocated
file handles exactly matches the number of used file handles.