IRCD-hybrid Connections Limited at 4026 - networking

Question

I'm running an Ubuntu Server 12.04 instance on EC2, with an installation of IRCD-hybrid 7.2 on it. Right now, I'm trying to load test the server by making a bunch on connections and seeing how much the server can handle. I have a script that connects to the room.
My problem is that I can get 4026 connections in the server maximum. My other socket connections just don't seem to work. I have the max clients set to 100k just to be safe and 50k for max number per ip.
When i run
sysctl fs.file-nr -> fs.file-nr = 4576 0 1513750
Also, my ulimits have been set:
ulimit -S -> 65536
My ulimit -n is 1024, but since I can get 4026 connections, I don't see how that's affecting it.
ulimit -n -> 1024
Memory and CPU are also nowhere even close to maximum when I run into this.
My code is this:
import random
import sys
import socket
import string
import time
n = ''.join(random.choice(string.letters) for i in xrange(40))
HOST="<MYHOST IS HERE>"
PORT=6666
NICK=n
IDENT=n
REALNAME=n
readbuffer=""
s=socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.connect((HOST, PORT))
s.send("NICK %s\r\n" % NICK)
s.send("USER %s %s %s :%s\r\n" % (IDENT, HOST, REALNAME, REALNAME))
s.send('JOIN #foobar\r\n')
while 1:
readbuffer=readbuffer+s.recv(1024)
temp=string.split(readbuffer, "\n")
readbuffer=temp.pop( )
for line in temp:
line=string.rstrip(line)
line=string.split(line)
if 'PRIVMSG' in line:
print line
if(line[0]=="PING"):
s.send("PONG %s\r\n" % line[1])
Is there a setting on ircd-hybrid that sets this? The terminal window says that "Server is full" when I try to connect with a regular client and I already have 4026 connections.

Answer 1

There are two types of ulimit, hard and soft. A ulimit on a particular resource may be increased up to the hard limit by the process. However it maybe listed no further.
On my box (ubuntu 12.04), the soft file descrption is 1024), but the hard limit is 4096
$ulimit -n
1024
moment#moment:~/tmp 20:26:04 0
$ulimit -n -H
4096
moment#moment:~/tmp 20:26:16 0
$ulimit -n -S
1024
It's entirely plausible that your irc server is increasing up to this hard limit.
A horrible hack to increase your ulimit temporarily works like this.
sudo su
ulimit -n 10000
su USERNAME
Long term you would need to increase the limit system wide or , preferably, increase the ulimit for just the process you are running. For daemons I normally do this using the ulimit instruction in upstart configuration files.
In general strace can be useful for debugging problems like this (this will probably show an earlier call to increase the file ulimit)