How to optimize apache web server for maximum concurrent connections or increase max clients in apache

Apache Performance Tuning

Apache 2.x is a general-purpose webserver designed to balance flexibility, portability, and performance. Although it has not been designed specifically to set benchmark records, Apache 2.x can perform high performance in many real-world situations.

Compared to Apache 1.3, release 2.x contains many additional optimizations to increase throughput and scalability. Most of these improvements are enabled by default. However, there are compile-time and run-time configuration choices that can significantly affect performance. MPM tuning is one of the upgrades that has been made in apache 2.x.

What are MPM’s

  • It modifies the basic functionality of the apache server related to multi-thread & multi-processes style of working.
  • It must be built into apache at compilation with http_core and mod_so modules.
  • Only one MPM can be loaded into the server at any time.

Choosing an MPM

Apache 2.x supports pluggable concurrency models, called Multi-Processing Modules (MPMs). When building Apache, you must choose an MPM to use. There are platform-specific MPMs for some platforms: beos, mpm_netware, mpmt_os2, and mpm_winnt. For general Unix-type systems, there are several MPMs from which to choose. The choice of MPM can affect the speed and scalability of the httpd. There are usually 2 types of MPM’s. Nowadays people tend to install apache 2.x that users worker MPM.

Different types of MPM

There are 2 types of MPM’s


  • Apache 1.3 based.
  • The prefork MPM uses multiple child processes, and each child process has only one thread, and ultimately one process/thread is handling one connection at a time.
  • Used for security and stability.
  • Has higher memory consumption and lower performance over the newer Apache 2.0-based threaded MPMs.


  • Apache 2.0 based.
  • The worker MPM uses multiple child processes, and each child process can have many threads, and each thread handles one connection at a time.
  • Worker generally is a good choice for high-traffic servers because it has a smaller memory footprint than the prefork MPM and has higher performance.
  • It does not provide the same level of isolation, i.e., request-to-request, as a process-based MPM does.

This newer Multi-Processing Module (MPM) implements a hybrid multi-process multi-threaded server. Using threads to serve requests can serve a large number of requests with fewer system resources than a process-based server. However, it retains much of a process-based server’s stability by keeping multiple processes available, each with many threads.

The most important directives used to control this MPM are ThreadsPerChild, which controls the number of threads deployed by each child process, and MaxClients, which controls the maximum total number of threads that may be launched.

How it works

Usually, I require that I want my apache to serve many concurrent users. Each user can fire a single request to an apache server, or a single user can fire many requests example, where a web page is requesting many image/javascript/css files. So now I want to increase this number.

This is the default worker-mpm configuration and i will tell, how to change parameters with increasing number of concurrent connections/requests/users

ServerLimit 16
StartServers 2
MaxClients 150
MinSpareThreads 25
MaxSpareThreads 75
ThreadsPerChild 25

First of all, whenever an apache is started, it will start 2 child processes determined by the StartServers parameter. Then each process will start with 25 threads determined by the ThreadsPerChild parameter, so this means 2 processes can service only 50 concurrent connections/clients, i.e., 25×2=50. If more concurrent users come, then another child process will start to serve another 25 users. But how many child processes can be started is controlled by the ServerLimit parameter. This means that in the configuration above, I can have 16 child processes in total, with each child process can handle 25 thread, in total handling 16×25=400 concurrent users. But if the number defined in MaxClients is less, which is 200 here, then this means that after 8 child processes, no extra process will start since we have defined an upper cap of MaxClients. This also means that if I set MaxClients to 1000, after 16 child processes and 400 connections, no extra process will start, and we cannot service more than 400 concurrent clients even if we have increased the MaxClient parameter. In this case, we need to also increase ServerLimit to 1000/25, i.e., MaxClients/ThreadsPerChild=40

So this is the optmized configuration to server 1000 clients

# worker MPM
# StartServers: initial number of server processes to start
# MaxClients: maximum number of simultaneous client connections
# MinSpareThreads: minimum number of worker threads which are kept spare
# MaxSpareThreads: maximum number of worker threads which are kept spare
# ThreadsPerChild: constant number of worker threads in each server process
# MaxRequestsPerChild: maximum number of requests a server process serves
<IfModule mpm_worker_module>
  ServerLimit         40
  StartServers        2
  MaxClients          1000
  MinSpareThreads     25
  MaxSpareThreads     75
  ThreadsPerChild     25
  MaxRequestsPerChild   0

Hardware and Operating System Issues with apache

The single biggest hardware issue affecting webserver performance is RAM. A webserver should never have to swap, as swapping increases the latency of each request beyond a point that users consider “fast enough.” This causes users to hit stop and reload, further increasing the load. You can, and should, control the MaxClients setting so that your server does not spawn so many children it starts swapping. This procedure for doing this is simple: determine the size of your average Apache process by looking at your process list via a tool such as top, and divide this into your total available memory, leaving some room for other processes.



The update cannot be installed because we will be unable to copy some files. This is usually due to inconsistent file permissions.: wp-admin/includes/update-core.php 2

Recently, we were trying to update a WordPress installation that was running under apache in a CentOS 7. When we would press the lovely blue button to update WordPress we would get the following error:

The update cannot be installed because we will be unable to copy some files. This is usually due to inconsistent file permissions.: wp-admin/includes/update-core.php

Installation Failed

At first we thought it was an issue with the privileges on the folder, so we did the following steps to fix the issue:

Find which user is controlling apache server:

We executed the following command to get the name of the local user that was handling the apache web server:

ps -ef | grep apache;

From which, we got the following results:

apache 7289 8523 1 10:35 ? 00:00:03 /usr/sbin/httpd -DFOREGROUND
apache 7293 8523 0 10:35 ? 00:00:02 /usr/sbin/httpd -DFOREGROUND
apache 7316 8523 0 10:35 ? 00:00:01 /usr/sbin/httpd -DFOREGROUND
apache 7317 8523 0 10:35 ? 00:00:01 /usr/sbin/httpd -DFOREGROUND
apache 7335 8523 1 10:35 ? 00:00:03 /usr/sbin/httpd -DFOREGROUND
apache 7347 8523 0 10:35 ? 00:00:01 /usr/sbin/httpd -DFOREGROUND
apache 7348 8523 0 10:35 ? 00:00:01 /usr/sbin/httpd -DFOREGROUND
apache 7349 8523 0 10:35 ? 00:00:01 /usr/sbin/httpd -DFOREGROUND
apache 7350 8523 0 10:35 ? 00:00:00 /usr/sbin/httpd -DFOREGROUND
apache 7351 8523 0 10:35 ? 00:00:01 /usr/sbin/httpd -DFOREGROUND
root 8071 7978 0 10:40 pts/1 00:00:00 grep --color=auto apache

The first column is the name of the user, so we found out that apache local user is the user executing the apache web server.

Repair all file and folder access rights:

After getting the above information we proceeded to update the access rights in our WordPress installation folder (/var/www/example.com)

find /var/www/example.com -type d -exec chmod 755 '{}' \;
find /var/www/example.com -type f -exec chmod 644 '{}' \;
chown -R apache:apache /var/www/example.com;

To our disappointment, nothing changed and we would still get the same error. Luckily enough we had another ace in our sleeve!

Checking the security context of each file and folder:

We executed the following command (ls -Z) to get the security context of the files and folders in the installation folder of WordPress:

ls -Z /var/www/example.com;

Where we got the following results:

drwxr-xr-x. apache apache unconfined_u:object_r:httpd_sys_content_t:s0 api
-rw-r--r--. apache apache unconfined_u:object_r:httpd_sys_content_t:s0 favicon.ico
-rw-r--r--. apache apache unconfined_u:object_r:httpd_sys_content_t:s0 index.php
-rw-r--r--. apache apache unconfined_u:object_r:httpd_sys_content_t:s0 license.txt
-rw-r--r--. apache apache unconfined_u:object_r:httpd_sys_content_t:s0 readme.html
-rw-r--r--. apache apache unconfined_u:object_r:httpd_sys_content_t:s0 r-file.php
-rw-r--r--. apache apache unconfined_u:object_r:httpd_sys_content_t:s0 wordfence-waf.php
-rw-r--r--. apache apache unconfined_u:object_r:httpd_sys_content_t:s0 wp-activate.php
drwxr-xr-x. apache apache unconfined_u:object_r:httpd_sys_content_t:s0 wp-admin
-rw-r--r--. apache apache unconfined_u:object_r:httpd_sys_content_t:s0 wp-blog-header.php
-rw-r--r--. apache apache unconfined_u:object_r:httpd_sys_content_t:s0 wp-comments-post.php
-rw-r--r--. apache apache unconfined_u:object_r:httpd_sys_content_t:s0 wp-config.php
-rw-r--r--. apache apache unconfined_u:object_r:httpd_sys_content_t:s0 wp-config-sample.php
drwxr-xr-x. apache apache unconfined_u:object_r:httpd_sys_rw_content_t:s0 wp-content
-rw-r--r--. apache apache unconfined_u:object_r:httpd_sys_content_t:s0 wp-cron.php
drwxr-xr-x. apache apache unconfined_u:object_r:httpd_sys_content_t:s0 wp-includes
-rw-r--r--. apache apache unconfined_u:object_r:httpd_sys_content_t:s0 wp-links-opml.php
-rw-r--r--. apache apache unconfined_u:object_r:httpd_sys_content_t:s0 wp-load.php
-rw-r--r--. apache apache unconfined_u:object_r:httpd_sys_content_t:s0 wp-login.php
-rw-r--r--. apache apache unconfined_u:object_r:httpd_sys_content_t:s0 wp-mail.php
-rw-r--r--. apache apache unconfined_u:object_r:httpd_sys_content_t:s0 wp-settings.php
-rw-r--r--. apache apache unconfined_u:object_r:httpd_sys_content_t:s0 wp-signup.php
-rw-r--r--. apache apache unconfined_u:object_r:httpd_sys_content_t:s0 wp-trackback.php
-rw-r--r--. apache apache unconfined_u:object_r:httpd_sys_content_t:s0 xmlrpc.php

What we got from this result: all files and folders marked with the httpd_sys_content_t are not directly editable by the apache web server even though the user has the rights to do so as it is a security step by SELinux.

Use this type for static web content, such as .html files used by a static website. Files labeled with this type are accessible (read only) to httpd and scripts executed by httpd. By default, files and directories labeled with this type cannot be written to or modified by httpd or other processes. Note that by default, files created in or copied into /var/www/html/ are labeled with the httpd_sys_content_t type.


The simple solution

We just changed the security context for the folders and files to httpd_sys_rw_content_t which allows apache web server to edit the files:

Files labeled with this type can be written to by scripts labeled with the httpd_sys_script_exec_t type, but cannot be modified by scripts labeled with any other type. You must use the httpd_sys_rw_content_t type to label files that will be read from and written to by scripts labeled with the httpd_sys_script_exec_t type.

chcon -R --type httpd_sys_rw_content_t /var/www/example.com;

After this command finished, we updated WordPress as normal!

(In case you want to change the security context back to the original just execute chcon with httpd_sys_content_t as parameter on the folders and files you want to operate as read-only).

Starting XAMPP with port 80 on Windows 10 Professional 1

Recently we were asked to have a look at a XAMPP installation on a Windows 10 Professional machine which would not start while giving the following error:

Problem detected!
Port 80 in use by "Unable to open process" with PID 4!
Apache WILL NOT start without the configured ports free!
You need to uninstall/disable/reconfigure the blocking application
or reconfigure Apache and the Control Panel to listen on a different port

The culprit of this problem was a module of the IIS (Internet Information Services for Windows Server) that is named World Wide Web Publishing Service (WWW service or W3SVC service). Apparently, the W3SVC was hoarding port 80 even though IIS was not executing. To provide a quick solution, we decided to stop the W3SVC and get over this difficulty in a jiffy.

As you can see in the following video, to stop the World Wide Web Publishing Service (WWW service or W3SVC service) we performed the next steps:

  1. Clicked on the Start button
  2. Typed in the word services, which showed the Services link which we clicked to start the windows services  manager
  3. Then, we scrolled down in the Services window until we found the World Wide Web Publishing Service
  4. Finally, we right clicked on it and selected Stop.

After that, XAMPP was able to start Apache on port 80 with no issues.


How To Install on GNU/Linux CentOS 7 the LAMP stack (Apache, MySQL, PHP) + phpMyAdmin

Following you will find the commands to perform the installation of the LAMP stack (Apache, MySQL, PHP) and phpMyAdmin on a GNU/Linux CentOS 7.
In this guide we kept the information to the bare minimum about what is what.


To perform the installation, please execute the following as a user with administrative rights:

#Update your system
sudo yum update -y;
#Install Apache, MariaDB (MySQL), PHP (with MySQL support and phpMyAdmin which is a free software tool written in PHP, intended to handle the administration of MySQL over the Web)
sudo yum install httpd mariadb-server mariadb php php-mysql phpmyadmin -y;
#Start Apache (PHP will start with Apache as module)
sudo systemctl start httpd;
#Enable Apache to start on boot
sudo systemctl enable httpd;
#Start MariaDB(MySQL)
sudo systemctl start mariadb;
#Enable MariaDB(MySQL) to start on boot
sudo systemctl enable mariadb;

Configuration of MariaDB (MySQL)

By now, your system should have all necessary packages installed and the services up and running.
Now it is best to configure your MariaDB (MySQL) in a way to disable some test data and test accounts and assign a password to your root user.
Execute the following to do so:

sudo mysql_secure_installation;

This tool will ask you for your current database root password. Since you just installed MariaDB (MySQL) you should not have one, so leave the field empty and press enter.
We recommend to answer with Y (Yes) in all of the security questions of this tool and set a strong password for your root user.

sudo mysql_secure_installation;

Following is the output we got from this tool:


In order to log into MariaDB to secure it, we'll need the current
 password for the root user.  If you've just installed MariaDB, and
 you haven't set the root password yet, the password will be blank,
 so you should just press enter here.

Enter current password for root (enter for none):
 OK, successfully used password, moving on...

Setting the root password ensures that nobody can log into the MariaDB
 root user without the proper authorisation.

Set root password? [Y/n] Y
 New password:
 Re-enter new password:
 Password updated successfully!
 Reloading privilege tables..
 ... Success!

By default, a MariaDB installation has an anonymous user, allowing anyone
 to log into MariaDB without having to have a user account created for
 them.  This is intended only for testing, and to make the installation
 go a bit smoother.  You should remove them before moving into a
 production environment.

Remove anonymous users? [Y/n] Y
 ... Success!

Normally, root should only be allowed to connect from 'localhost'.  This
 ensures that someone cannot guess at the root password from the network.

Disallow root login remotely? [Y/n] Y
 ... Success!

By default, MariaDB comes with a database named 'test' that anyone can
 access.  This is also intended only for testing, and should be removed
 before moving into a production environment.

Remove test database and access to it? [Y/n] Y
 - Dropping test database...
 ... Success!
 - Removing privileges on test database...
 ... Success!

Reloading the privilege tables will ensure that all changes made so far
 will take effect immediately.

Reload privilege tables now? [Y/n] Y
 ... Success!

Cleaning up...

All done!  If you've completed all of the above steps, your MariaDB
 installation should now be secure.

Thanks for using MariaDB!

Configuration of the firewall

Executing the following will enable access to your web-server from the network for http and https.

sudo firewall-cmd --permanent --zone=public --add-service=http;
sudo firewall-cmd --permanent --zone=public --add-service=https;
sudo firewall-cmd --reload;

Location of files / Where to upload your website

In CentOS 7, the directory where the website pages are located is at /var/www/html/.
You can place your html and php code there.

Configuration of phpMyAdmin

phpMyAdmin should be available at http://<IP of the web server>/phpmyadmin
The access to phpMyAdmin is controlled by the Apache Virtual Host File for phpMyAdmin that is found here /etc/httpd/conf.d/phpMyAdmin.conf.
By default, this configuration file only allows access to phpMyAdmin from the localhost (
In case you want to access it from another machine, you need to modify this file.
Before doing any changes, make a backup of the original file first:

 sudo cp /etc/httpd/conf.d/phpMyAdmin.conf /etc/httpd/conf.d/phpMyAdmin.conf.original;

To enable access only for a specific IP

Edit the Apache Virtual Host File for phpMyAdmin (/etc/httpd/conf.d/phpMyAdmin.conf) and change every reference of with the IP address of the machine you want to give access to.

There should be four lines that you need to change.
In our installation it was the following lines:

  1. 17Require ip
  2. 25Allow from
  3. 34Require ip
  4. 42Allow from

Then restart the Apache service to apply the changes:

sudo systemctl restart httpd;

To enable access to any IP

Delete the existing file and create a new one.

sudo rm /etc/httpd/conf.d/phpMyAdmin.conf;
sudo touch /etc/httpd/conf.d/phpMyAdmin.conf;

Using the editor of your choice add the following content and save it:

Alias /phpMyAdmin /usr/share/phpMyAdmin
Alias /phpmyadmin /usr/share/phpMyAdmin

<Directory /usr/share/phpMyAdmin/>
 AllowOverride None
 Options None
 Allow from All
 Require all granted

Then restart the Apache service to apply the changes:

sudo systemctl restart httpd;

Following is the original content of our Apache Virtual Host File for phpMyAdmin (/etc/httpd/conf.d/phpMyAdmin.conf)

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$ cat /etc/httpd/conf.d/phpMyAdmin.conf
 # phpMyAdmin - Web based MySQL browser written in php
 # Allows only localhost by default
 # But allowing phpMyAdmin to anyone other than localhost should be considered
 # dangerous unless properly secured by SSL

Alias /phpMyAdmin /usr/share/phpMyAdmin
Alias /phpmyadmin /usr/share/phpMyAdmin

<Directory /usr/share/phpMyAdmin/>
 AddDefaultCharset UTF-8

 <IfModule mod_authz_core.c>
  # Apache 2.4
   Require ip
   Require ip ::1
 <IfModule !mod_authz_core.c>
  # Apache 2.2
  Order Deny,Allow
  Deny from All
  Allow from
  Allow from ::1

<Directory /usr/share/phpMyAdmin/setup/>
 <IfModule mod_authz_core.c>
  # Apache 2.4
   Require ip
   Require ip ::1
 <IfModule !mod_authz_core.c>
  # Apache 2.2
  Order Deny,Allow
  Deny from All
  Allow from
  Allow from ::1

# These directories do not require access over HTTP - taken from the original
# phpMyAdmin upstream tarball
 <Directory /usr/share/phpMyAdmin/libraries/>
  Order Deny,Allow
  Deny from All
  Allow from None

<Directory /usr/share/phpMyAdmin/setup/lib/>
  Order Deny,Allow
  Deny from All
  Allow from None

<Directory /usr/share/phpMyAdmin/setup/frames/>
 Order Deny,Allow
 Deny from All
 Allow from None

# This configuration prevents mod_security at phpMyAdmin directories from
# filtering SQL etc.  This may break your mod_security implementation.
#<IfModule mod_security.c>
#    <Directory /usr/share/phpMyAdmin/>
#        SecRuleInheritance Off
#    </Directory>

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