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Open File Limit Calculator

Work out open file limit instantly with clear inputs, formula shown and shareable results.

About Open File Limit Calculator

There are two separate limits: fs.file-max caps descriptors system-wide, and the nofile rlimit caps them per process. Hitting the system limit returns ENFILE and affects every process; hitting the per-process limit returns EMFILE and affects only one. Each open descriptor also costs kernel memory, so a very high limit has a real cost when actually used.

Formula

Descriptor accounting

total = processes x descriptors per process; kernel memory = total x bytes per descriptor; compare against fs.file-max

Worked example

With the default values below, Open File Limit Calculator returns Total open descriptors system-wide of 33,600. Change any input above and every figure here is recalculated in your browser.

Inputs used

Processes on the hostminimum 1
240
Average open descriptors per processminimum 1
140
Configured fs.file-maxminimum 1,024
1,048,576
Kernel memory per open descriptorminimum 64 bytes
1,024 bytes

Results

Total open descriptors system-wide
33,600
Share of fs.file-max used
3.20%
Kernel memory for open files
32.81 MiB
Assessment
Within safe limits

Step by step

  1. 1Values used
  2. 2Descriptor accounting
  3. 3Total open descriptors system-wide= 33,600
  4. 4Share of fs.file-max used= 3.20
  5. 5Kernel memory for open files= 34,406,400
  6. 6Assessment= Within safe limits

Assumptions and limits

  • The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

What is the difference between EMFILE and ENFILE?

EMFILE means the process hit its own nofile rlimit; ENFILE means the system-wide fs.file-max is exhausted. They need different fixes.

How do I find which process is leaking descriptors?

Compare /proc/PID/fd counts across processes, or use lsof grouped by process. A steadily growing count with no corresponding workload growth is a leak.

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