# Apache HTTP Server — Configure and Operate the Web Server > Practical guide to the Apache HTTP Server — service control, configtest, virtual hosts, modules, TLS and directives on Debian/Ubuntu and RHEL. Source: https://www.jpkc.com/db/en/cheatsheets/web-servers/apache/ The Apache HTTP Server – often simply called httpd – has been one of the most widely deployed web servers on the internet for decades. Its modular design lets you switch on features like mod_rewrite, SSL or reverse proxying exactly where you need them, and VirtualHosts let you serve any number of domains from a single instance. This cheat sheet collects the commands you reach for daily: service control, configuration tests, modules, VirtualHosts, TLS and performance tuning. Always validate your syntax with `apachectl configtest` before a reload – and prefer `graceful` over a hard restart to avoid dropping live connections. ## Service Management (systemctl) `systemctl start apache2` — Start the Apache web server (Debian/Ubuntu). Use httpd on RHEL/CentOS. ```bash systemctl start apache2 ``` `systemctl stop apache2` — Stop the Apache web server gracefully. ```bash systemctl stop apache2 ``` `systemctl restart apache2` — Restart Apache (stops and starts). Drops all active connections briefly. ```bash systemctl restart apache2 ``` `systemctl reload apache2` — Reload Apache configuration without dropping active connections (graceful). ```bash systemctl reload apache2 ``` `systemctl status apache2` — Show Apache service status, PID, and recent log output. ```bash systemctl status apache2 ``` `systemctl enable apache2` — Enable Apache to start automatically on system boot. ```bash systemctl enable apache2 ``` `systemctl disable apache2` — Disable Apache from starting automatically on boot. ```bash systemctl disable apache2 ``` ## apachectl Commands `apachectl configtest` — Test the Apache configuration for syntax errors. Returns 'Syntax OK' or an error. ```bash apachectl configtest ``` `apachectl -t` — Short alias for configtest. Test configuration syntax. ```bash apachectl -t ``` `apachectl -t -D DUMP_VHOSTS` — Show a summary of all configured virtual hosts with their ServerName and document roots. ```bash apachectl -t -D DUMP_VHOSTS ``` `apachectl -t -D DUMP_MODULES` — List all loaded Apache modules. ```bash apachectl -t -D DUMP_MODULES ``` `apachectl -t -D DUMP_RUN_CFG` — Show the resolved runtime configuration (MPM settings, ServerName, etc.). ```bash apachectl -t -D DUMP_RUN_CFG ``` `apachectl -v` — Show the Apache version and build date. ```bash apachectl -v ``` `apachectl -V` — Show the Apache version, build flags, and compiled-in defaults. ```bash apachectl -V ``` `apachectl graceful` — Reload Apache configuration gracefully (without dropping connections). ```bash apachectl graceful ``` `apachectl graceful-stop` — Stop Apache gracefully after current requests complete. ```bash apachectl graceful-stop ``` ## Modules (Debian/Ubuntu) `a2enmod ` — Enable an Apache module. Creates symlinks in mods-enabled/. Requires reload/restart. ```bash a2enmod rewrite ``` `a2dismod ` — Disable an Apache module. Removes symlinks from mods-enabled/. Requires reload. ```bash a2dismod status ``` `a2enmod rewrite && systemctl reload apache2` — Enable mod_rewrite and reload Apache in one step. ```bash a2enmod rewrite && systemctl reload apache2 ``` `a2enmod ssl headers deflate expires` — Enable multiple modules at once. ```bash a2enmod ssl headers deflate expires ``` `apache2ctl -M` — List all currently loaded (static and shared) Apache modules. ```bash apache2ctl -M ``` `apache2ctl -M | grep ` — Check whether a specific module is currently loaded. ```bash apache2ctl -M | grep rewrite ``` ## Virtual Hosts (Debian/Ubuntu) `a2ensite ` — Enable a virtual host config file from sites-available/. Creates symlink in sites-enabled/. ```bash a2ensite example.com.conf ``` `a2dissite ` — Disable a virtual host config file. Removes symlink from sites-enabled/. ```bash a2dissite 000-default.conf ``` `a2ensite example.com.conf && systemctl reload apache2` — Enable a virtual host and reload Apache in one step. ```bash a2ensite example.com.conf && systemctl reload apache2 ``` `ls /etc/apache2/sites-enabled/` — List all currently enabled virtual host configurations. ```bash ls /etc/apache2/sites-enabled/ ``` `ls /etc/apache2/sites-available/` — List all available virtual host configuration files. ```bash ls /etc/apache2/sites-available/ ``` `apachectl -t -D DUMP_VHOSTS 2>&1 | grep -A3 'example.com'` — Find which vhost config handles a specific domain. ```bash apachectl -t -D DUMP_VHOSTS 2>&1 | grep -A3 'example.com' ``` ## Logs `tail -f /var/log/apache2/access.log` — Follow the Apache access log in real-time (Debian/Ubuntu). ```bash tail -f /var/log/apache2/access.log ``` `tail -f /var/log/apache2/error.log` — Follow the Apache error log in real-time. ```bash tail -f /var/log/apache2/error.log ``` `tail -f /var/log/httpd/access_log` — Follow the Apache access log on RHEL/CentOS. ```bash tail -f /var/log/httpd/access_log ``` `grep 'error\|crit\|alert\|emerg' /var/log/apache2/error.log` — Search the error log for critical and error-level messages. ```bash grep 'error\|crit\|alert\|emerg' /var/log/apache2/error.log ``` `apache2ctl status` — Show a live server status page in the terminal (requires mod_status). ```bash apache2ctl status ``` `apachectl -e debug -k start` — Start Apache with debug-level error logging for troubleshooting. ```bash apachectl -e debug -k start ``` ## SSL / TLS `a2enmod ssl && a2ensite default-ssl.conf && systemctl reload apache2` — Enable SSL module and the default SSL virtual host (Debian/Ubuntu). ```bash a2enmod ssl && a2ensite default-ssl.conf && systemctl reload apache2 ``` `openssl req -x509 -nodes -days 365 -newkey rsa:2048 -keyout server.key -out server.crt` — Generate a self-signed SSL certificate valid for 365 days. ```bash openssl req -x509 -nodes -days 365 -newkey rsa:2048 -keyout server.key -out server.crt ``` `openssl s_client -connect :443 -servername ` — Test an SSL connection and inspect the certificate chain. ```bash openssl s_client -connect example.com:443 -servername example.com ``` `openssl x509 -in server.crt -text -noout` — Display the details of an SSL certificate file (expiry, issuer, SANs). ```bash openssl x509 -in server.crt -text -noout ``` `certbot --apache -d ` — Obtain and install a Let's Encrypt SSL certificate for Apache automatically. ```bash certbot --apache -d example.com -d www.example.com ``` `certbot renew --dry-run` — Test the automatic Let's Encrypt certificate renewal process. ```bash certbot renew --dry-run ``` ## Configuration Directories `/etc/apache2/apache2.conf` — Main Apache configuration file on Debian/Ubuntu. ```bash nano /etc/apache2/apache2.conf ``` `/etc/httpd/conf/httpd.conf` — Main Apache configuration file on RHEL/CentOS/Fedora. ```bash nano /etc/httpd/conf/httpd.conf ``` `/etc/apache2/sites-available/` — Directory containing all virtual host definition files (Debian/Ubuntu). ```bash ls /etc/apache2/sites-available/ ``` `/etc/apache2/conf-available/` — Directory for additional configuration snippets (Debian/Ubuntu). ```bash ls /etc/apache2/conf-available/ ``` `/etc/apache2/mods-available/` — Directory containing all available module configuration files. ```bash ls /etc/apache2/mods-available/ ``` `a2enconf && systemctl reload apache2` — Enable a configuration snippet from conf-available/. ```bash a2enconf php8.2-fpm && systemctl reload apache2 ``` `a2disconf ` — Disable a configuration snippet from conf-enabled/. ```bash a2disconf security ``` ## Virtual Host Configuration Basic HTTP virtual host block with server name, document root, and separate log files. ```bash ServerName example.com ServerAlias www.example.com DocumentRoot /var/www/html/example ErrorLog ${APACHE_LOG_DIR}/example-error.log CustomLog ${APACHE_LOG_DIR}/example-access.log combined ``` HTTPS virtual host block with SSL certificate configuration. ```bash ServerName example.com SSLEngine on SSLCertificateFile /etc/ssl/certs/example.crt SSLCertificateKeyFile /etc/ssl/private/example.key DocumentRoot /var/www/html/example ``` Directory block granting access and enabling .htaccess overrides (AllowOverride All). ```bash Options Indexes FollowSymLinks AllowOverride All Require all granted ``` Hide Apache version and OS from HTTP headers and error pages (add to apache2.conf). ```bash ServerTokens Prod ServerSignature Off ``` Reverse proxy: forward /api/ requests to a backend app on port 3000 (requires mod_proxy). ```bash ProxyPass /api/ http://localhost:3000/ ProxyPassReverse /api/ http://localhost:3000/ ``` ## Performance & Tuning `apache2ctl -V | grep 'MPM'` — Check which MPM (Multi-Processing Module) is active: prefork, worker, or event. ```bash apache2ctl -V | grep 'MPM' ``` `a2dismod mpm_prefork && a2enmod mpm_event && systemctl restart apache2` — Switch from prefork to the high-performance event MPM (required for HTTP/2). ```bash a2dismod mpm_prefork && a2enmod mpm_event && systemctl restart apache2 ``` `a2enmod http2 && systemctl reload apache2` — Enable HTTP/2 support (requires mpm_event and SSL). ```bash a2enmod http2 && systemctl reload apache2 ``` `ab -n 1000 -c 10 https://example.com/` — Apache Bench: send 1000 requests with 10 concurrent connections to benchmark a URL. ```bash ab -n 1000 -c 10 https://example.com/ ``` `ab -n 500 -c 20 -H "Accept-Encoding: gzip" http://example.com/` — Benchmark with gzip encoding header to test compression performance. ```bash ab -n 500 -c 20 -H "Accept-Encoding: gzip" http://example.com/ ``` `curl -I -H 'Accept-Encoding: gzip' http://example.com/` — Check whether gzip compression (mod_deflate) is active for a URL. ```bash curl -I -H 'Accept-Encoding: gzip' http://example.com/ ``` ## Conclusion Apache remains the robust, broadly supported choice for classic web hosting – especially where `.htaccess` overrides, mature modules and decades of documentation matter. Always check configuration changes with `apachectl configtest` first and roll them out with a `graceful` reload, so your server stays stable even under live traffic. When you need maximum performance, pair the event MPM with HTTP/2 and mod_deflate. ## Further Reading - [Apache HTTP Server – official documentation](https://httpd.apache.org/docs/) – reference and manual - [Apache HTTP Server – Wikipedia](https://en.wikipedia.org/wiki/Apache_HTTP_Server) – background and history ## Related Commands - [caddy](https://www.jpkc.com/db/en/cheatsheets/web-servers/caddy/) – modern web server with automatic HTTPS - [certbot](https://www.jpkc.com/db/en/cheatsheets/web-servers/certbot/) – obtain and renew Let's Encrypt certificates - [ferron](https://www.jpkc.com/db/en/cheatsheets/web-servers/ferron/) – lightweight web server written in Rust