Vhosts and server blocks basics
Last updated on: 2021-07-12
Authored by: Coral Moore
This article introduces you to vhost and server block basics.
Check the web server status
The most common web servers that run on Linux® are Apache® (httpd or apache2) and NGINX®. Plesk® is a GUI platform for managing websites. If you have Plesk installed, use this article as a guide to understand vhosts.
By default, web servers allow HTTP traffic through port
80 and HTTPS
(secure) traffic through port
To find the webserver that runs on ports
443, enter the following command:
# netstat -plnt | awk '$4 ~ /:(80|443)$/' tcp6 0 0 :::80 :::* LISTEN 2549/httpd tcp6 0 0 :::443 :::* LISTEN 2549/httpd
To check the the status of a webserver, run one of the commands shown in the following table:
|Type of webserver||Command|
In Plesk, to check the status and identify which web server is in use, enter the following command:
# service psa status; netstat -plnt | awk '$4 ~ /:(80|443)$/'
Check the vhosts configuration
A web server (or a pool of web servers) can host several websites by using Virtual Hosts (vhosts). Vhosts allow several websites to share resources from a physical server.
Vhosts can be IP-based or name-based. IP-based vhosts assign a different IP address to a website, and name-based vhosts assign multiple hostnames to a single IP address. Vhosts keep track of websites in a web server, specifying the configuration of each website.
To check the vhosts configuration in Apache, enter one of the following commands:
# httpd -S
# apache2ctl -S *:80 example.com (/etc/httpd/vhost.d/example.com.conf:1)
To read the contents of a vhost configuration file, enter the following command:
# cat /etc/httpd/vhost.d/example.com.conf
Entries in the vhosts configuration file include:
- :80 or :443: These entries specify if the website uses HTTP (
80) or HTTPS (
- DocumentRoot: The directory path of the website files.
- ServerName: The website domain name.
- ServerAlias: Any other website domain name which you want to redirect to the ServerName domain. You usually use domains of the type www.domain, but you can also use other domains or subdomains.
- ErrorLog: The directory path and name of error logs.
- Port 443: The SSL configuration. Comment this section if the website does not have a valid SSL certificate.
- SSL files: The three SSL file paths needed for a secure HTTPS server.
The following example shows a vhosts configuration file:
<VirtualHost *:80> DocumentRoot "/var/www/vhosts/example.com/httpdocs" ServerName "example.com" ServerAlias "www.example.com" <Directory /var/www/vhosts/example.com/httpdocs> AllowOverride All Options +FollowSymlinks </Directory> DirectoryIndex index.html index.php index.htm # Logging CustomLog /var/log/httpd/example.com-access_log combined ErrorLog /var/log/httpd/example.com-error_log </VirtualHost> #<VirtualHost *:443> # DocumentRoot "/var/www/vhosts/example.com/httpdocs" # ServerName "example.com" # ServerAlias "www.example.com" # <Directory /var/www/vhosts/example.com/httpdocs> # AllowOverride All # Options +FollowSymlinks # </Directory> # DirectoryIndex index.html index.php index.htm # # SSL Configuration # SSLEngine On # SSLCertificateFile /etc/httpd/conf/ssl.crt/2021-example.com.crt # SSLCACertificateFile /etc/httpd/conf/ssl.crt/2021-example.com.ca # SSLCertificateKeyFile /etc/httpd/conf/ssl.key/2021-example.com.key # # # Logging # CustomLog /var/log/httpd/example.com-ssl_access_log combined # ErrorLog /var/log/httpd/example.com-ssl_error_log #</VirtualHost>
To copy the configuration file of an existing vhost to create a new one, enter the following command:
# cat /OLD_DOMAIN.conf | sed 's/OLD_DOMAIN/NEW_DOMAIN/ig' >> /NEW_DOMAIN.conf
Edit the new vhost configuration file as required. For example, you might
need to comment the settings that make port
To find the location of DocumentRoot in a vhost configuration file, enter the following command:
# grep Doc /etc/httpd/vhost.d/example.com.conf DocumentRoot /var/www/vhosts/example.com
Make a new vhost
Use the following instructions to make a new vhost:
If possible, copy an existing vhost to keep consistent settings. Use a text editor or tool like
Make a new DocumentRoot directory. The system makes the custom and error logs automatically. Run the following command:
# mkdir -p /docroot
Check that the web server does not send any errors:
# httpd -t
Do a graceful restart on the web server to incorporate the changes with minimal disruption to your live environment:
# service httpd graceful
Check the web server again:
# httpd -t; service httpd status
Check and troubleshoot changes to the vhost configuration
To check mistakes in Apache, use either one of the following commands:
# httpd -t
# apache2ctl -t AH00558: httpd: Could not reliably determine the server's fully qualified domain name, using 127.0.0.1. Set the 'ServerName' directive globally to suppress this message Syntax OK
To check mistakes in NGINX, use the following command:
# nginx -t AH00558: httpd: Could not reliably determine the server's fully qualified domain name, using 127.0.0.1. Set the 'ServerName' directive globally to suppress this message Syntax OK
Note: The clause Could not reliably determine is common, and it doesn’t mean an error. You can usually ignore it.
The following example shows a sample error:
# httpd -t AH00112: Warning: DocumentRoot [/var/www/vhosts/example.com] does not exist AH00558: httpd: Could not reliably determine the server's fully qualified domain name, using 127.0.0.1. Set the 'ServerName' directive globally to suppress this message Syntax OK
Fix this error by creating a DocumentRoot:
# mkdir -p /var/www/vhosts/example.com
Another example error:
# httpd -t AH00526: Syntax error on line 5 of /etc/httpd/vhost.d/example.com.conf: Invalid command 'oops', perhaps misspelled or defined by a module not included in the server configuration
The word oops is in the vhost file, and Apache does not know how to interpret it. You can use vim, nano, or another text editor to fix the error.
Restart a web server
The web server acknowledges the changes made to the vhosts configuration after a restart. The current threads can finish before the restart occurs with the graceful option.
To do a graceful restart on Apache, enter one of the following commands:
# service httpd graceful
# service apache2 graceful
The following are best practices to avoid service interruptions after changing the vhosts configuration:
- Back up the webserver.
- Make the changes.
- Do a graceful restart.
- Ensure that the webserver runs without errors.
It is important to avoid as much downtime as possible in a live environment, which means that after restarting the web server, you should perform the checks as quickly as possible. To do this, group all the commands on one line.
To do a graceful restart on Apache and check for errors, enter either one of the following commands:
# service httpd graceful; httpd -t; service httpd status | grep running
# service apache2 graceful; apache2ctl -t; service apache2 status | grep running AH00558: httpd: Could not reliably determine the server's fully qualified domain name, using 127.0.0.1. Set the 'ServerName' directive globally to suppress this message Syntax OK Redirecting to /bin/systemctl status httpd.service Active: active (running) (Result: exit-code) since Mon 2021-01-18 12:53:06 GMT; 2 months 19 days ago
To restart NGINX and check that it’s running, enter the following commands:
# nginx -s reload; nginx -t; service nginx status
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