Mosquitto increasing maximum connection limit
<p>I am trying to increase the maximum open file connection of Mosquitto broker. But I read that increasing concurrent connections are not controlled by Mosquitto only.
As per our study we decided for 100k concurrent connection, we are targeting 1.6 GB RAM.  But for testing I have to increase from default 1024 connections to 20000
Testing environment configurations:
t2. micro AWS server with  64 MB 14.04 ubuntu operating system. Changing connection limit in the mosquitto configuration is not reflecting. What can be the reason? 
Do we need to change any configuration related to AWS Server?</p>

<p>My configurations:</p>

<p>Our system wide open connections is configured on <code>/etc/sysctl.conf</code>:</p>

<pre><code>fs.file-max =99905
</code></pre>

<p>Running the command <code>sysctl -p</code> or <code>cat /proc/sys/fs/file-max</code> is reflecting the changes </p>

<p>In <code>/etc/security/limits.conf</code>:</p>

<pre><code>ubuntu          hard     nofile         45000
ubuntu          soft     nofile         35000
</code></pre>

<p>Mosquitto is installed under the user 'Ubuntu' .</p>

<p>We also added below line of code on <code>/etc/pam.d/common-session</code></p>

<pre><code>session required pam_limits.so
</code></pre>

<p>Running <code>ulimit -a</code> is giving the below result:</p>

<pre><code>core file size          (blocks, -c) 0
data seg size           (kbytes, -d) unlimited
scheduling priority             (-e) 0
file size               (blocks, -f) unlimited
pending signals                 (-i) 7859
max locked memory       (kbytes, -l) 64
max memory size         (kbytes, -m) unlimited
open files                      (-n) 35000
pipe size            (512 bytes, -p) 8
POSIX message queues     (bytes, -q) 819200
real-time priority              (-r) 0
stack size              (kbytes, -s) 8192
cpu time               (seconds, -t) unlimited
max user processes              (-u) 7859
virtual memory          (kbytes, -v) unlimited
file locks                      (-x) unlimited
</code></pre>

<p>My init configuration file for mosquitto in <code>/etc/init/mosquitto.conf</code></p>

<pre><code>description "Mosquitto MQTTv3.1 broker"
author "Roger Light &lt;roger@atchoo.org"

start on net-device-up

respawn

exec /usr/sbin/mosquitto -c /etc/mosquitto/mosquitto.conf
#limit nofile 4096 4096

limit nofile 24000  24000
</code></pre>

<p>Below is the configuration in <code>/etc/mosquitto/mosquitto.conf</code>:      </p>

<pre><code># change user to root
user ubuntu         

set_ulimit () {
    ulimit -f unlimited
    ulimit -t unlimited
    ulimit -v unlimited
    ulimit -n 24000
    ulimit -m unlimited
    ulimit -u 24000
}

start)
    ...
    # Update ulimit config in start command
    set_ulimit
    ...
    ;;
  stop)
</code></pre>

<p>But running <code>cat /proc/4957/limits</code> is still showing default value 1024 open files:</p>

<pre><code>Limit                     Soft Limit           Hard Limit           Units
Max cpu time              unlimited            unlimited            seconds
Max file size             unlimited            unlimited            bytes
Max data size             unlimited            unlimited            bytes
Max stack size            8388608              unlimited            bytes
Max core file size        0                    unlimited            bytes
Max resident set          unlimited            unlimited            bytes
Max processes             7859                 7859                 processes
Max open files            1024                 4096                 files
Max locked memory         65536                65536                bytes
Max address space         unlimited            unlimited            bytes
Max file locks            unlimited            unlimited            locks
Max pending signals       7859                 7859                 signals
Max msgqueue size         819200               819200               bytes
Max nice priority         0                    0
Max realtime priority     0                    0
Max realtime timeout      unlimited            unlimited            us
</code></pre>

<p>4957 -is the process id of Mosquitto</p>