This article introduces you to vhost and web server basics. A web server runs software to process web pages. After web traffic has reached the server, it follows steps to reach the right website. If a server serves web content, you
need to install a web server.

Check the web server status

The most common web servers that run on Linux® are Apache® (httpd or apache2) and NGINX®. You might also have Plesk®. You can use Plesk to manage your websites in a more point-and-click Windows® style. If you install Plesk, use the rest of this article an overview of vhosts because you need to use Plesk instead of the Linux command line to perform the tasks described here.

By default, web servers allow HTTP traffic through port 80 and HTTPS (secure) traffic through port 443.

To find the web server that runs on ports 80 and 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 web server, run one of the commands shown in the following table:

To check for Plesk and see which web server is running, 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-address-based or name-based. IP-address-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

or

# 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 (443).
• DocumentRoot: The directory path of the website files. This is most often the location where developers need access to upload files.
• ServerName: The website domain name.
• ServerAlias: Any other website domain name that 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.
• Secure HTTPS site: The three SSL file paths needed for full encryption to turn it into a more secure HTTPS site.

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 out the settings that make port 443 active.

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:

1. If possible, copy an existing vhost to keep consistent settings. Use a text editor, such as vim, nano, sed, or awk, if you need to edit it.

      # cat /OLD_DOMAIN.conf | sed 's/OLD_DOMAIN/NEW_DOMAIN/ig' >> /NEW_DOMAIN.conf
   

2. Make a new DocumentRoot directory. The system makes the custom and error logs automatically. Run the following command:

   # mkdir -p /docroot
   

3. Check that the web server does not send any errors:

   httpd -t

4. Do a graceful restart on the web server to incorporate the changes with minimal disruption to your live environment:

   # service httpd graceful
   

5. The smallest change in a vhost can interrupt your entire web server and stop it from serving all of your websites. For that reason, use one of the following commands to re-check the web server:

   Type of web server	Command
   httpd	# httpd -t; service httpd status
   apache2	# apache2ctl -t; service apache2 status
   nginx	# nginx -t; service nginx status

Check and troubleshoot changes to the vhost configuration

To check mistakes in Apache, use either one of the following commands:

# httpd -t

or

# 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 directory:

# 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

or

# service apache2 graceful

Sometimes, the smallest change in a vhost can interrupt your entire web server and stop it from serving all of your websites. So back up your work, and after doing a graceful restart to recognize changes, ensure that your web server still runs without errors.

The following are best practices to avoid service interruptions after changing the vhosts configuration:

• Back up the web server.
• Make the changes.
• Do a graceful restart.
• Ensure that the web server runs without errors.

In a live environment, the key is to avoid as much downtime as possible, which means that you need to do a graceful restart on the web server and run your checks as quickly as possible so that you can undo your changes if needed. To do this, you can 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

or

# 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

Use the Feedback tab to make any comments or ask questions. You can also start a conversation with us.