“WARNING: soft rlimits too low” in MongoDB with Mac OS X

If you get this warning when you connect to mongo shell in Mac OS X:

** WARNING: soft rlimits too low. Number of files is 256, should be at least 1000

A simple way to fix this is setting the limit just before starting mongod with this:

ulimit -n 1024 && mongod

Or this:

launchctl limit maxfiles 1024 1024

But if you are running mongo in a development environment this shouldn’t be a problem, you can just ignore it.

This is a temporary and not very pretty fix. To make this permanent you have to add this to the /etc/launchd.conf file:

launchctl limit maxfiles 1024 1024

Now reboot to make changes effective.

You can see the actual values of the limits running this:

$ launchctl limit maxfiles
        maxfiles    1024           1024

Remember to restart your mongod process every time you change any value to see if it works.