After configuring Apache server settings on the name server, you may encounter a message “[warn] NameVirtualHost 192.168.1.3:80 has no VirtualHosts”

The issue may be due to more than one entry of NameVirtualHost lines in the configuration settings. You can find this out by

$ grep NameVirtual * -R
site1:NameVirtualHost *:80
site2:NameVirtualHost *:80

Linux Solution: Remove one of the occurance of the NameVirtualHost and the warning message that you receive will vanish.

$ ls -l | egrep ‘^d’

Usage: In addition to the different flavors of Linux in the market, comes the usage of Linux. Some variants are developed as Desktops and a major as servers. In addition to that, there are virtual appliances that are packaged with other applications for easy deployment across environments. The choice is many and the usage determines the choice of the Linux flavor in most cases.

Client Support: All distributions are open source – FREE for usage. Red Hat and Ubuntu are maintained by organizations which provide commercial support which bigger organizations prefer. CentOS, Debian, Fedora are maintained by volunteers.

Commands used: For an administrator it will be easy if ALL the systems in the network use the same distribution. Some commands that are used to achieve a functionality are not consistent across distributions.

Packaging: Feature enhancements, application patches, software installation and management differ from one distribution to the other making the need for the administrator to remember the subtle keys.

To add users to the already existing password file, use the command
$ htpasswd -m /secured/.mypass username2

When additional users are added to the password file, ensure that you don’t use the “-c” option.

Read Password protect directories here

To list the current set of aliases simply type
$ alias

To display the set alias for a specified alias name, type
$ alias alias-shortstring
Example:
$ alias ls

To set an alias you use the format
$ alias shortstring = “linux command string”

For example,
$ alias ls=”ls -1″

After setting alias for “ls” if we want to get the default “ls” command operation then use
$ \ls

To unset the alias command, use
$ unalias ls

To unset all aliases that are set
$ unalias *

Apache configuration file has two lines (listed below) in /etc/apache2/apache2.conf which does that

# Include generic snippets of statements
Include /etc/apache2/conf.d/

# Include the virtual host configurations:
Include /etc/apache2/sites-enabled/

Consider the ServerName to be “myserver”. Check /etc/hosts for an entry

127.0.0.1 localhost
192.168.1.100 myserver.com myserver
…

We will see an example where by we can change/add apache ports in order to have two sites hosted on different ports.

Example:
http://myserver:8001

http://myserver:8002

First, we need to edit ports.conf file to add two port numbers 8001, 8002

$ vi /etc/apache2/ports.conf

File Content

Listen 80
Listen 8001
Listen 8002

Listen 443

Now, ports.conf file is configured to listen on 80, 8001, 8002

Restart apache for the changes to take effect
$ /etc/init.d/apache2 restart

To check if Apache is listening on the correct port, netstat command comes in handy

$ netstat -tulpn
$ netstat -tulpn | grep :8002

Setup two site location in /var/www
$ mkdir /var/www/site1
$ cd /var/www/site1
$ echo “In site1″ > index.html

$ mkdir /var/www/site2
$ cd /var/www/site2
$ echo “In site2″ > index.html

Now, lets create myserver.conf file in /etc/apache2/sites-available with the content shown below

ServerName greenland
DocumentRoot /var/www/site1

ServerName greenland
DocumentRoot /var/www/site2

Create a symbolic link to enable the site in sites-enabled folder
$ cd /etc/apache2/sites-enabled
$ ln -s ../sites-available/myserver.conf myserver.conf

In Debian, a2ensite and a2dissite comes in handy to enable, disable sites

Again, restart apache for the changes to take effect
$ /etc/init.d/apache2 restart

In the browser, type

http://myserver:8001

http://myserver:8002

to see the two sites in action.

The above error message basically means that eth0 i.e your network interface card is not setup correctly.

Some of the commands that can come handy in troubleshooting where the error lies are listed below

$ dmesg | grep eth0
(displays information about the ethernet controller card, mac address etc.)

$ cat /etc/sysconfig/network(displays the network settings)
NETWORKING=yes
HOSTNAME=localhost.localdomain
GATEWAY=192.168.122.1

$ cat /etc/sysconfig/network-scripts/ifcfp-eth0

$ ifconfig eth0 down (to down the nic)
$ ifconfig eth0 up (to start the nic)
$ netstat -rn (display kernel routing IP table)
$ cat ifcfg-eth0 (eth0 configuration settings)
DEVICE=eth0
BOOTPROTO=dhcp
HWADDR=00:16:18:33:B3:CF
ONBOOT=yes

$ service network restart (restart the network settings)

$ ping -c4 google.ca(to check if the internet connection works)

$ traceroute google.ca (to check how the IP navigation path is set)

Refer Red Hat linux 5 configure network article for additional info

“stty” is the command that is used to reset your screen content.

$ stty sane

For e.g. lets find where “samba” is located in a CentOS server

$ which samba
which command searches the list of programs listed down through the PATH settings

$ whereis samba
whereis command also searches for programs that are not present in the PATH setting