Network Administration

This article explains how to configure Apache Web Server in Linux step by step with examples.

Apache is the most popular, secure, robust, reliable and powerful web server. Apache is used by more websites than all other web servers combined.

Topic explained in this tutorials are following:-

  • HTTP/HTTPS
  • Configure a virtual host.
  • Configure private directories.
  • Deploy a basic CGI application.
  • Configure group-managed content.

In this tutorial I will use three systems Server, linuxclient and windowclient from our LAB environment. I will configure Apache Web Server on Server system and test from inuxclient and windowclient system. If you want to check the network topology used in this article please check following article. Lab set up for RHCE 6 practice

Installation of Apache

Two packages are required for Apache server

  • httpd
  • mod_ssl
  • elinks

httpd package install Apache web server.

mod_ssl is the additional package which required to create secure websites

elinks is the additional package for text based web browser.

If you have yum repository configured use following command to install Apache web server with additional package

# yum install –y httpd mod_ssl

yum-httpd

# yum install elinks

yum-elinks

Or you can do it in more simpler way by using groupinsatall. With following command you can install mandatory and all default packages.

# yum groupinstall "Web Server"

yum-groupinstall-httpd

If yum repository is not configured use rpm command to install necessary RPM. Mount installation disk of RHEL6 in media folder and move in Packages folder.

cd-media-packages

Run following command to install httpd

#rpm -ivh httpd* --nodeps --force

rpm-httpd

Run following command to install mod_ssl

#rpm -ivh mod_ssl* --nodeps --force

rpm-mod-ssl

Run following command to install elinks

#rpm -ivh elinks* --nodeps --force

rpm-elink

Verify that the packages were installed correctly

verfiy-rpm

Run following command to start service when the system boots

chkconfig-httpd-on

Start httpd service

arp-scok-add-fail

httpd service requires at least one active network connection, if it does not detect any active connection it will throw following message

Starting httpd: httpd: apr_sockaddr_info_get() failed for Server

httpd service try to resolve system IP with domain name. It will throw following error, If it fails to resolve.

httpd: Could not reliably determine the server's fully qualified domain name, using 127.0.0.1 for ServerName

In real world DNS Server are used to bind IP address with domain name. In LAB environment where we have limited systems , we can also use hosts file for this purpose.

Open /etc/sysconfig/network

etc-sysconfig-network

Change hostname to Server.example.com and save the file

sysconfig-entry

Reboot the system

reboot

Verify that hostname is changed

ipaddress-hostname-server

Before we update hosts file on server also verify the hostname and ip address of linuxclient

ipaddress-hostname-client

Now on server open /etc/hosts file

etc-hosts

Add entry for server and linuxclient system and save the file

hosts-entry

Verify the network card status

service-network-status

Now restart the httpd service

service-httpd-restart

Default versions of httpd create a generic web server service which is sufficient for most basic operations. Once httpd service is running start web browser and enter a URL http://localhost

apache-test-page-server

Same testing can be done form text based web browser ,If GUI is unavailable.

# elinks 127.0.0.1

elinks-localhost

We got Apache test page which confirm successful Apache configuration.

apache-test-page-command-line

Exit from the ELinks browser. Press Q, and when the Exit ELinks text menu appears, press Y to exit Elinks.

We have successfully installed Apache Web Server. So far its a generic web server service, to make it a regular and a secure web server, we need to configure it.

IPTABLES Firewall rules for web Server

Default installation of Apache web server use port 80 for HTTP traffic and 443 for HTTPS traffic.

You can create custom iptables rule to limit access to one or more networks or systems. For example following rules allows access to every computers on 192.168.1.0 network except one with IP address 192.168.1.25 over port 80.

-A INPUT -m state --state NEW -m tcp -p tcp -s 192.168.1.25 --dport 80 -j REJECT
-A INPUT -m state --state NEW -m tcp -p tcp -s 192.168.1.0/24 --dport 80 -j ACCEPT

We have a well written article for IPTABLES firewall, use that to create custom firewall rules for web server. For this article create rules to allow all traffic on port 80 and 443.

#iptables -A INPUT -m state --state NEW -m tcp -p tcp --dport 80 -j ACCEPT
#iptables -A INPUT -m state --state NEW -m tcp -p tcp --dport 443 -j ACCEPT

iptables-httpd-rules

Save the firewall rules you have just created and restart the iptables service

# service iptables save
# service iptables restart

iptables-save-restart

Until you change the value of DocumentRoot directive in httpd.conf file , Apache looks for web pages in default location /var/www/html directory.

To get your web server up and running, all you need to do is to transfer the web pages or websites in /var/www/html directory.

We will make two websites for testing. RHCE exam does not test your ability to make websites. Its only test your ability to configure and run web server. You can use most simple html web page for testing.

Make two directories mysite1 and mysite2 in /var/www/html folder

mkdir-mysite

Make a sample html page in both directories

cat-index-htm

Our sample websites are ready for use.

Configure SELinux for web server

Use following command to check all associated SELinux Booleans with httpd

getsebool-httpd

Most of these options are self explained and relate to interactions with other services. for example httpd_enable_ftp_server allow Apache to act as an FTP server, which is out of scope for this article.

getsebool-httpd-list

Default enabled SELinux options

BooleansDescriptions
httpd_builtin_scripting Used to provide permission for php content
httpd_dbus_avahi Supports access from HTTP services
httpd_enable_cgi Allows HTTP services to execute GCI scripts
httpd_tty_comm Enables communication with controlling terminals
httpd_unified Supports read/write/execute access by httpd_t files

httpd_enable_homedirs supports access to files from user home directories, default value is off. We will enable it later in this article.

Default enabled options are sufficient to provide basic web services , you do not need to make any changes. But you need to configure SELinux contexts, user context is system_u and the type is http_sys_content_t.

Check the current context of the files

#ls -Z /var/www
#ls -Z /var/www/html

ls-z

We need to set context of any newly created file or directory for the web server user to be able to access it.

Use the chcon command to change the context

#chcon -R -u system_u /var/www/html
#chcon -R -t httpd_sys_content_t /var/www/html/

Verify that all the context fields have been changed correctly

#ls -Z /var/www/html

chcon

Test these websites form linuxclient system [make sure client system have elinks rpm installed]

elinks 192.168.1.1/mystie1/index.htm

start-elinks

Verify the site

elink-test

Close elinks

eixt-from-elink

On window client open browser and type 192.168.1.1/mysite2/index.htm

internet-explore

We have set up Apache web server with default configuration.

Back up the default httpd.conf file on a safe location.

mkdir-backup

Open the /etc/httpd/conf/httpd.conf

vi-httpd-conf

This is the main configuration file for httpd web service and completely usable right out of the box for generic web service.

This file is grouped in three sections and each section is well commented

  • Global environment directives that control the whole operation of Apache server process.
  • Directives that define the parameters of the main or default server, which responds to requests that are not handled by a virtual host. These directives also provide default values for the settings of all virtual hosts.
  • Settings for virtual hosts, which allow Web requests to be sent to different IP addresses or hostnames and have them handled by the same Apache server process.

To make navigation easier, turn on line number ESC Key + : +set nu + Enter Key

set-nu

Host-Based Security

If server have multiple IP address, you can limit the IP address and port on which the server can listen for incoming connection. By default server listen on port 80, but can be update as well.

default-listen

For example to limit server only to listen on IP address 192.168.1.1 with port 80 Set Listen Directive

Listen 192.168.1.1:80

listen-changed

Now Server will listen only on the 192.168.1.1 IP address on port 80 for incoming requests.

Apache also let you configure the hosts which should be allow to access to web server. <Directory> section allow you to specify the hosts base security.

ValueExampleDescriptions
Allow from all Default value, allow access from all hosts
Allow from [IP Address] Allow from 192.168.1.10 To allow only a specific IP or host
Allow from [Host name] Allow from linuxclient To allow only specific host
Allow from [Network] Allow from .example.com To allow only example.com network
Allow from [Network] 192.168.1.0/24
192.168.1.0/255.255.255.0
To allow only from 192.168.1.0 network
Deny from all Deny access from all hosts
Deny from [IP Address] Deny from 192.168.1.10 To Deny only a specific IP or host
Deny from [Host name] Deny from linuxclient To deny only specific host
Deny from [Network] Deny from .example.com To deny only example.com network
Deny from [Network] 192.168.1.0/24
192.168.1.0/255.255.255.0
To deny only from 192.168.1.0 network

For exam remember

  • If DNS service is unreliable use IP address.
  • When specify domain name to allow or deny from, make sure you include the leading dot[.]
  • When specify a subnet, there is no ending dot[.] at last octet.
  • Order play the most important role, when set allow or deny access.
  • If you set Order allow, deny Only those host names or IP addresses associated with allow directive are allowed access. All remaining hosts or IP address would be denied.
  • If you set Order deny, allow Only those host names or IP addresses associated with deny directive are denied access. All remaining hosts or IP address would be allowed.

Default value is Allow from all

default-allow-from-entry

In our LAB setup we have two clients linuxclient [192.168.1.10], and windowclient [192.168.1.20]. Lets allow access only to linuxclient system.

allow-from-entry

Save the file and restart the httpd service

httpd-service-restart

Try to access same websites again from both client systems. This time linuxclient system would be able to access web server as usual, but on windowsystem you will be denied

windowclient-error

User-Based Security

User based authentication provides a way to allow only certain users or group to access web server.

In exam you can use following options to configure user based authentication.

Options Descriptions
AuthType Defines the authentication method
AuthName Comment for the users
AuthUserFile File used to define username and password
AuthGroupFile File used to define groups
Require Specifies the users or groups that can log in

Open httpd.conf file again

vi-httpd-conf

In last practice we have restricted all hosts except one

allow-from-entry

Before we do this exercise lets allow all hosts to access the web server.

default-allow-from-entry

In < directory > section add following and save the file

AuthType Basic
AuthName “Password Restricted Area”
AuthUserFile /etc/httpd/userauthfile
Require user rhceuser01

require-user1

Use htpasswd command to create a userauthfile, that will be holds user accounts.

# htpasswd -cm /etc/httpd/userauthfile rhceuser01

useradd-rhceuser01

-c Create new file and populates it with first user and password.

-m Passwords will be encrypted in MD5 before saving

Do not use -c options for creating subsequent users, otherwise it will completely override the file. Use -c option only first time for first user, from second users do not use -c option.

Restart the web server

service-httpd-restart

Try again to access same sites from client, this time it will ask for user name and password

ask-for-pass

If you cancel or use wrong user name and password, access would be denied

auth-require

Use correct user name and password

type-pass

Upon successful authentication access would be granted

sucess-get

Secure web server with .htaccess file

In previous exercise we have secured entire sites. However in real life you want to allow certain parts of site publicly accessible, while other by only authenticated users. For this we will use .htaccess file.

Open /etc/httpd/conf/httpd.conf file again

vi-httpd-conf

Change AllowOverride directive value to authconfig

allow-override-none

In previous example we did user base authentication

Remove that and save the file

allow-override-authconfig

Make a directory and file under mysite1

mkdir /var/www/html/mysite1/salary

mkdir-salary

Suppose that salary folder contains the salary sheet of employees and we want to allow only hr group to access it.

Create a .htaccess file in the salary folder

#vi /var/www/html/mysite1/salary/.htaccess

vi-htaccess

Add followings and save the file

AuthType Basic
AuthName “Password Restricted Area”
AuthGroupFile /etc/httpd/rhcegroupfile
Require group hr

htaccess-entry

Now only users from hr group, defined in /etc/httpd/rhcegroupfile can assess this.

Create few more accounts

useradd-hruser

Create rhcegroupfile, this file will hold entry for groups

vi-rhcegroup

Add user accounts in hr group and save file

rhcegroup-entry

Update the SELinux context of .htaccess file

chcon-htaccess

Restart the web server

httpd-service-restart

Try again to access site for client, access to other parts of site are allowed except salary

mysite-homepage

To access salary folder you need to provide user name and password

htaccess-ask-pass

Upon successful authentication access would be granted

salary-sheet-htm

Configure public_html folder in user home directory

httpd.conf file includes a commented directive UserDir public_html just under the default UserDir disable , when it's enabled, it allows users to browse and access the public_html directory within their home folder.

Open /etc/httpd/conf/httpd.conf file

vi-httpd-conf

Comment the default directive

userdir-disable

Uncomment the UserDir public_html directive and save the file

userdir-public-html

Now anyone will have access to web pages that a user puts in his ~/public_html directory. This option can be useful if you want each user to share files over the Web. For this option you need to make users home directory executable for world. You also need to make public_html readable and executable. By default this option is disable because this requires a bit of security compromise. So unless you need to be able to share content out of a users home directory, do not enable this option. If you have to enable it in real world, take all caution in setting up this option.

Create a new normal user

useradd-rh-user1

Make public_html folder under his home folder and create a test file in public_html folder

mkdir-public-html

Change file permission

chmod-public-html

Enable SELinux Boolean associated with home directory

set-bool-http-enable-homedir

Restart the web server

httpd-service-restart

Access it from client system by typing 192.168.1.1/~rh_user1/index.htm

access-home-dir

How to create virtual hosts

Virtual host feature of Apache allows you to define multiple web sites on single IP address. For Virtual hosts configuration following options are required

NameVirtualHost Hostname or IP address of the virtual host
ServerAdmin Email address of the webmaster
DocumentRoot Location of the directory, which holds virtual host files
ServerName URL of the virtual host
ErrorLog Location for the error log
CustomLog Location for a custom log

Suppose that we want to host a new website example.com in virtual host.

Make new directory which will hold our new site

mkdir-webdata

Make a sample file in new site

mkdir-webdata-cat-sample-file

Update SELinux context

chchon-webdata

Open main configuration file again

vi-httpd-conf

By default NameVirtualHost directive is disabled

namehost-commented

Enable it

namehost-uncomment

At the end of file in virtual host section add following lines and save the file

<VirtualHost *:80>
ServerAdmin webmaster@example.com
DocumentRoot /webdata/example.com
ServerName example.com
ErrorLog logs/example.com-error_log
CustomLog logs/example.com-access_log common
</VirtualHost>

virtual-host-entry

If you have DNS server configured update the zone files, otherwise update the hosts files . On server open the /etc/hosts file

etc-hosts

Add entry for new virtual host site and save the file

host-entry-server

Restart the httpd service

httpd-service-restart

On linuxclient system you also need to update the hosts file before testing. Open hosts file

vi-etc-host-linuxclient

Add entry for new virtual host site and save the file

hosts-entry-linuxclient

Now use elinks command to browse new site

elink-example-com

Test page confirms that we have successfully configured virtual host.

virtual-host-testing-client

How to deploy a basic CGI application

In this section we will deploy a basic CGI application. RHCE exam objective "Deploy a basic CGI application", does not test your programming skills, so you need not to worry about programming language. You only need to know the method.

Create a directory to hold your web application:

# mkdir /var/www/webapp

mkdir-webapp

Make a new sample perl file

vi-hello-pl

Add following in file and save the file. [This will make a sample perl script to print hello, world. Based on Apache manual]

#!/usr/bin/perl
print "Content-type: text/html\n\n";
print "Hello, World!";

hello-pl-entry

Update file permission and SELinux context

chmod-chcon-webapp

Open configuration file

vi-httpd-conf 

At end of file add following and save the file

ScriptAlias /webapp "/var/www/webapp"
<Directory "/var/www/webapp/">
Options ExecCGI FollowSymLinks
Order allow,deny
Allow from all
</Directory>

cgi-bin-entry

Restart the web server

httpd-service-restart

On client now you can access this CGI application.

webapp-testing

Configure secure virtual host

In this last section of tutorial we will configure a secure virtual host with self signed certificate. Make a directory to host our secure site

mkdir-secure-host1

Make a sample index.htm file in it

cat-secure-index

Change file permission and Update SELinux context

chcon-secure

Open main configuration file /etc/httpd/conf.d/ssl.conf

vi-ssl-conf

Make sure Listen Directive remain on

listen-443

Add new Directive NameVirtualHost *:443 just above the <VirtualHost _default_:443> and replace _default_ with * in <VirtualHost _default_:443> tag.Uncomment the DocumentRoot and ServerName directives.

namevirtualhost

Change the value of directives and save the file

ssl-uncomment-documentroot

Move in certificate holder directory /etc/pki/tls/certs and use genkey command to generate new certificate and private key for secure site

genkey

Select Next and press enter on Keypair generation window

keypair-next

During the exam always choose minimum available key size. Even smaller key size can take up to several minutes and in exam every minute is precious. Select 512 and move to Next tab and press enter

choose-key-size

Wait while key generates

genrating-key

Select No and press enter on Generate CSR window

genrate-crs

Keep default details and select Next and press Enter

details-for-certificate

We have sucessfully created the certificate ,now we to update the hosts file on server

host1-host-entry

Restart the httpd service

httpd-service-restart

On client updated the hosts file

linuxclient-host1-entry-host-file

To test secure site open the web browser and type https://host1.example.com/index.htm in URL

untursted-connection

You will see Untrusted connection screen Unless you purchase an actual certificate from a certificate authority (CA) such as VeriSign and Thawte. For RHCE exam we do not need third party certificate, as we have self signed certificate. Click on I Understand the Risks and Click on Add Exception

add-exception

Click on confirm security exception

confirm-security

Test page confirms that we have successfully configured the secure virtual host

secure-test-page

To test secure sites form elinks test based browser we need to comment two standard directives

open /etc/elinks.conf file

linuxclient-vi-elinks-conf

You need to comment these directives

linuxclient-elinks-conf-uncommented

Comment them and save the file

linuxclient-elinks-conf-commented

Now you can access secure sites form elinks as well

linuxclient-elinks-test-host-index

Test page confirms our secure web hosting

linuxclient-elinks-test-page

When you restarts the httpd service, restart process actually stop the service from running before starting it again. This process hardly take few seconds that is ok for exam purpose but in real life where thousands of people are hitting your site, you can't afford any outage even its in seconds. In that situation you can use reload option which allows the main configuration to reread without the actually bringing service down.

#service httpd reload

One more important option which should know for real world is graceful

#service httpd graceful

This option reread the new configuration file without disconnecting any currently connected users. Only drawback of this option is that the currently active connections use the old configuration file until they terminate their connection and reconnect.

One more cool options is configtest, when used , service parses the main config file for any errors and reports back if something is found. It's your helping hand during the exam to detect any syntax errors in configuration file.

# service httpd configtest
Syntax OK

If this command detect any syntax related error it return with that, otherwise it return with Syntax ok.

That's all for this article I hope you have enjoyed this. You can check more RHCE 6 related articles here .
RHCE 6 Study Guide Network administration