/proc/sys/fs/file-max

Linux的/proc/sys/fs/file-max決定了當前內核可以打開的最大的文件句柄數。

查看當前的值：

cat /proc/sys/fs/file-max

這個值在kernel的文檔里是這樣描述的：

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一般為記憶體大小（KB）的10%來計算，如果使用shell，可以這樣計算：

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

一般我們不需要主動設置這個值，除非這個值確實較小（可能有各種其他原因導致file-max沒有設置為記憶體的10%）

如何查看當前kernel的句柄:

cat /proc/sys/fs/file-nr

file-nr在內核文檔里得解釋如下：

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.