The kernel allocates file handles dynamically, but as yet it doesn‘t free them again.
内核可以动态的分配文件句柄，但到目前为止是不会释放它们的
The value in file-max denotes the maximum number of file handles that the Linux kernel will allocate. When you get lots of error messages about running out of file handles, you might want to increase this limit.
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.
