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一般為內存大小（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沒有設置為內存的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.