Apache HTTP Server Cheatsheet

Apache HTTP Server (httpd or apache2) is one of the most widely used web servers in the world.

Installation

# Debian / Ubuntu
sudo apt install apache2
 
# RHEL / CentOS / Fedora
sudo dnf install httpd

Service Management

# Debian / Ubuntu (service name: apache2)
sudo systemctl enable --now apache2   # Start and enable on boot
sudo systemctl status apache2        # Check status
sudo systemctl restart apache2       # Restart (drops connections)
sudo systemctl reload apache2        # Reload config gracefully
 
# RHEL / CentOS (service name: httpd)
sudo systemctl enable --now httpd
sudo systemctl status httpd
sudo systemctl restart httpd
sudo systemctl reload httpd

Configuration File Locations

Debian / Ubuntu:
- Main Config: /etc/apache2/apache2.conf
- Virtual Hosts: /etc/apache2/sites-available/ and /etc/apache2/sites-enabled/
- Modules: /etc/apache2/mods-available/
- Document Root: /var/www/html/
RHEL / CentOS:
- Main Config: /etc/httpd/conf/httpd.conf
- Virtual Hosts: /etc/httpd/conf.d/
- Document Root: /var/www/html/

Testing Configuration Syntax

Before reloading or restarting, always test for syntax errors.

# Debian / Ubuntu
sudo apache2ctl configtest
 
# RHEL / CentOS
sudo apachectl configtest

Enabling / Disabling Modules and Sites (Debian/Ubuntu)

Debian/Ubuntu uses helper scripts to manage configurations.

# Enable/Disable a site (Virtual Host)
sudo a2ensite example.com.conf
sudo a2dissite 000-default.conf
 
# Enable/Disable an Apache module
sudo a2enmod rewrite       # Enable mod_rewrite for URL rewriting
sudo a2enmod ssl           # Enable mod_ssl for HTTPS
sudo a2dismod autoindex    # Disable directory listing module
 
# Enable/Disable a configuration snippet
sudo a2enconf security
sudo a2disconf security
 
# Always reload after changing configuration
sudo systemctl reload apache2

Basic Virtual Host (`/etc/apache2/sites-available/example.com.conf`)

<VirtualHost *:80>
    ServerAdmin [email protected]
    ServerName example.com
    ServerAlias www.example.com
    DocumentRoot /var/www/example.com/public_html
 
    ErrorLog ${APACHE_LOG_DIR}/error.log
    CustomLog ${APACHE_LOG_DIR}/access.log combined
 
    <Directory /var/www/example.com/public_html>
        Options -Indexes +FollowSymLinks
        AllowOverride All
        Require all granted
    </Directory>
</VirtualHost>

SSL / HTTPS Virtual Host

# Enable SSL module and default SSL site (Debian/Ubuntu)
sudo a2enmod ssl
sudo a2ensite default-ssl
sudo systemctl reload apache2

Custom SSL Virtual Host (/etc/apache2/sites-available/example.com-ssl.conf):

<VirtualHost *:443>
    ServerName example.com
    DocumentRoot /var/www/example.com/public_html
 
    SSLEngine on
    SSLCertificateFile    /etc/letsencrypt/live/example.com/fullchain.pem
    SSLCertificateKeyFile /etc/letsencrypt/live/example.com/privkey.pem
 
    <Directory /var/www/example.com/public_html>
        Options -Indexes +FollowSymLinks
        AllowOverride All
        Require all granted
    </Directory>
</VirtualHost>
 
# Redirect HTTP to HTTPS
<VirtualHost *:80>
    ServerName example.com
    Redirect permanent / https://example.com/
</VirtualHost>

URL Rewriting (mod_rewrite)

Enable mod_rewrite first: sudo a2enmod rewrite

In Virtual Host or `.htaccess`

RewriteEngine On
 
# Redirect www to non-www
RewriteCond %{HTTP_HOST} ^www\.example\.com [NC]
RewriteRule ^(.*)$ https://example.com/$1 [R=301,L]
 
# Remove .html extension from URLs
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME}.html -f
RewriteRule ^(.*)$ $1.html [L]

.htaccess

.htaccess provides per-directory configuration overrides. Requires AllowOverride All in the Virtual Host.

# Deny access to a file
<Files "config.php">
    Require all denied
</Files>
 
# Password protect a directory
AuthType Basic
AuthName "Restricted Area"
AuthUserFile /etc/apache2/.htpasswd
Require valid-user

Create the password file:

# Create a new htpasswd file with user 'admin'
sudo htpasswd -c /etc/apache2/.htpasswd admin
 
# Add another user to an existing file (no -c flag)
sudo htpasswd /etc/apache2/.htpasswd anotheruser

Logs

# Debian / Ubuntu
tail -f /var/log/apache2/access.log
tail -f /var/log/apache2/error.log
 
# RHEL / CentOS
tail -f /var/log/httpd/access_log
tail -f /var/log/httpd/error_log

Cheatsheets