Q:

How do I change the number of open files limit in Linux?

When running my application I sometimes get an error about too many files open.
Running ulimit -a reports that the limit is 1024.  How do I increase the limit above 1024?  
Edit
ulimit -n 2048 results in a permission error.

A:

You could always try doing a ulimit -n 2048.  This will only reset the limit for your current shell and the number you specify must not exceed the hard limit
Each operating system has a different hard limit setup in a configuration file.  For instance, the hard open file limit on Solaris can be set on boot from /etc/system.
set rlim_fd_max = 166384
set rlim_fd_cur = 8192

On OS X, this same data must be set in /etc/sysctl.conf.
kern.maxfilesperproc=166384
kern.maxfiles=8192

Under Linux, these settings are often in /etc/security/limits.conf.
There are two kinds of limits:

soft limits are simply the currently enforced limits
hard limits mark the maximum value which cannot be exceeded by setting a soft limit

Soft limits could be set by any user while hard limits are changeable only by root.
Limits are a property of a process. They are inherited when a child process is created so system-wide limits should be set during the system initialization in init scripts and user limits should be set during user login for example by using pam_limits.
There are often defaults set when the machine boots.  So, even though you may reset your ulimit in an individual shell, you may find that it resets back to the previous value on reboot.  You may want to grep your boot scripts for the existence ulimit commands if you want to change the default. 

A:

If you are using Linux and you got the permission error, you will need to raise the allowed limit in the /etc/limits.conf or /etc/security/limits.conf file (where the file is located depends on your specific Linux distribution). 
For example to allow anyone on the machine to raise their number of open files up to 10000 add the line to the limits.conf file. 
* hard nofile 10000
Then logout and relogin to your system and you should be able to do:
ulimit -n 10000 
without a permission error. 

A:

1) Add the following line to /etc/security/limits.conf
webuser hard nofile 64000

then login as webuser
su - webuser

2) Edit following two files for webuser
append .bashrc and .bash_profile file by running
echo "ulimit -n 64000" >> .bashrc ; echo "ulimit -n 64000" >> .bash_profile

3) Log out, then log back in and verify that the changes have been made correctly:
$ ulimit -a | grep open
open files                      (-n) 64000

Thats it and them boom, boom boom.

