sysctl -a | grep fs.file
fs.file-nr = 39392 0 372197
fs.file-max = 372197
nr就是已经用的，今天有需要，找了一把，记录一下
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file-max & file-nr:
The kernel allocates file handles dynamically, but as yet it
doesn't free them again.
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.
The three values in file-nr denote the number of allocated
file handles, the number of unused file handles and the maximum
number of file handles. When the allocated file handles come
close to the maximum, but the number of unused file handles is
significantly greater than 0, you've encountered a peak in your
usage of file handles and you don't need to increase the maximum.
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