Apple - Which command controls the open file limits?

The simple answer used to be that there were multiple limits and the lowest limit that you reach in a specific instance will generate your error. Now on 10.12 launchctl limit maxfiles is also in the mix. For details on implementation, this great answer is getting bounty and deserves more votes than the one I can give it.

other relevant threads are:

• `ulimit -n` for non-root
• Why won't kern.maxfiles setting in /etc/sysctl.conf stick?

The ulimit level is set low to prevent one poor shell script from flooding the kernel with open files.

The kern.maxfilesperproc is there to leave a little room in the max files count so that one process can use most but not all of the open file handler space from the kernel.

For normal situations, the kern.maxfiles is the final limiting factor.

On Sierra - the limits are 256 open files and unlimited max, so I'm finding that having 3 to 4 thousand files set for the soft limit works for just about all our hardware and still keeps the system responsive when a runaway process opens too many files. We do like to keep our development servers at the 256 limit so that we catch leaky and problematic software in development / staging and test rather than finding out about it in production.

• http://krypted.com/mac-os-x/maximum-files-in-mac-os-x/

I'm not a fan of 10k files - maybe with APFS and NVMe storage we will see the day when that's not unthinkable, but try to stick with hundreds or low thousands for your file limits. Especially if your mac has a low process limit, having so many files opened by so few processes can be problematic.

It seems like there is an entirely different method for changing the open files limit for each version of OS X.

For OS X Sierra (10.12.X) you need to:

1. In Library/LaunchDaemons create a file named limit.maxfiles.plist and paste the following in (feel free to change the two numbers (which are the soft and hard limits, respectively):

<?xml version="1.0" encoding="UTF-8"?>  
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN"  
        "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">  
  <dict>
    <key>Label</key>
    <string>limit.maxfiles</string>
    <key>ProgramArguments</key>
    <array>
      <string>launchctl</string>
      <string>limit</string>
      <string>maxfiles</string>
      <string>64000</string>
      <string>524288</string>
    </array>
    <key>RunAtLoad</key>
    <true/>
    <key>ServiceIPC</key>
    <false/>
  </dict>
</plist> 

2. Change the owner of your new file:

sudo chown root:wheel /Library/LaunchDaemons/limit.maxfiles.plist

3. Load these new settings:

sudo launchctl load -w /Library/LaunchDaemons/limit.maxfiles.plist

4. Finally, check that the limits are correct:

launchctl limit maxfiles

The following should resolve most common problems (and are listed in order of their hierarchy):

echo 'kern.maxfiles=20480' | sudo tee -a /etc/sysctl.conf
echo -e 'limit maxfiles 8192 20480\nlimit maxproc 1000 2000' | sudo tee -a /etc/launchd.conf
echo 'ulimit -n 4096' | sudo tee -a /etc/profile

Notes:

1. You will need to restart for these changes to take effect.
2. AFAIK you can no longer set limits to 'unlimited' under OS X
3. launchctl maxfiles are bounded by sysctl maxfiles, and therefore cannot exceed them
4. sysctl seems to inherit kern.maxfilesperproc from launchctl maxfiles
5. ulimit seems to inherit it's 'open files' value from launchctl by default
6. you can set a custom ulimit within /etc/profile, or ~/.profile ; while this isn't required I've provided an example
7. Be cautious when setting any of these values to a very high number when compared with their default - the features exist stability/security. I've taken these example numbers that I believe to be reasonable, written on other websites.