The following shows how to increase the maxfiles (maximum number of open files) soft limit, but the same process can be applied to any system limit. On Linux these are set using sysctl.

Increasing per-process (launchd)

If an individual launchd process needs a higher soft limit, adding the following to its .plist will do nicely:

    <key>SoftResourceLimits</key>
        <dict>
            <key>NumberOfFiles</key>
            <integer>10240</integer>
        </dict>

Of course, this may fall apart if the .plist can be restored to its default version by a software update.

Cunning Plan™: Create a LaunchDaemon or cron job to run a script every night that checks the .plist and inserts the above if it’s not there (easy to do using XMLStarlet), then restarts the relevant daemon.

Increasing globally

Too low a value of maxfiles can cause things like mysqldump to fail (no backups for you, although MariaDB seems to set it independently these days). To show the current limit (probably stupidly low, e.g., 256):

launchctl limit maxfiles

To set temporarily:

sudo launchctl limit maxfiles 10240 2147483647

The third and fourth arguments are the soft and hard limits, respectively. Always set the fourth argument to 2147483647 (= INT_MAX = “unlimited”) unless you really want your machine to grind to a halt (https://apple.stackexchange.com/a/366319)! As per the launchctl man page (emphasis added):

“When a given resource is specified, it prints the limits for that resource. With a third argument, it sets both the hard and soft limits to that value. With four arguments, the third and forth [sic] argument represent the soft and hard limits respectively.”

To set more persistently (https://superuser.com/a/1171028), create /Library/LaunchDaemons/limit.maxfiles.plist with the following contents:

<?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>10240</string>
      <string>2147483647</string>
    </array>
    <key>RunAtLoad</key>
    <true/>
    <key>ServiceIPC</key>
    <false/>
  </dict>
</plist>

However, note that this only occurs somewhere during the startup sequence, not first, so servers (e.g., MySQL) may start earlier and therefore need to be restarted in order to inherit the new value.

Checking

To check the open files limit in MySQL:

select @@open_files_limit;