How to properly increase a `ulimit -n` limits? I'm trying to download the X-Plane 10 Demo through uTorrent, however I get a "too many open files" error all the time. I can do the alternate download (which takes forever and a day), but I wonder how I can increase the setting in Lion?

I found conflicting information about it, some say that ulimit -n and sysctl are the tools of choice, while others report that launchctl is correct.

The reported value for ulimit -n is 256, same for launchctl limit:

cpu         unlimited      unlimited      
filesize    unlimited      unlimited      
data        unlimited      unlimited      
stack       8388608        67104768       
core        0              unlimited      
rss         unlimited      unlimited      
memlock     unlimited      unlimited      
maxproc     709            1064           
maxfiles    256            unlimited
The following should resolve most solutions (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:


You will need to restart for these changes to take effect.
AFAIK you can no longer set limits to 'unlimited' under OS X
launchctl maxfiles are bounded by sysctl maxfiles, and
therefore cannot exceed them
sysctl seems to inherit kern.maxfilesperproc from launchctl
maxfiles
ulimit seems to inherit it's 'open files' value from
launchctl by default
you can set a custom ulimit within /etc/profile, or
~/.profile ; while this isn't required I've provided an example
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. 
When launchctl limits are lower than the sysctl ones, there have been reports that the relevent sysctl ones will be bumped up automatically to meet the requirements.