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.

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.

user@server:~# less /var/log/apache2/error.log

Postfix configuration screen throws you with the following options to choose from
i) No changes (no changes to configuration settings)
ii) Internet site (Mail sent and received using SMTP)
iii) Internet with smarthost (Mail sent to another machine called smarthost)
iV) Satellite system (All mail sent to another machine for delivery)
v) Local only (No network based mail system. Only applied to this local machine)

For this example let us choose the option (iv) where we have a Linux server connected to external network through another server.

Step 2: sudo dpkg-reconfigure postfix

Next screen will ask you for the “System mail name”. Give the name of the mail server in this location. Go with the default options.

To test if the configuration has gone through successfully I have used two methods. One using telnet and other using sendmail program.

root@greenland:/# telnet mail-server 25
Trying 172.24.8.11…
Connected to mail-server.domain.com.
Escape character is ‘^]’.
220 mailserver.domain.com Microsoft ESMTP MAIL Service, Version: 6.0.3790.3959 ready at Thu, 6 Aug 2009 12:36:38 -0400
helo gmail.com
250 mail.domain.com Hello [192.168.1.116]
mail from: tester@gmail.com
250 2.1.0 tester@gmail.com….Sender OK
rcpt to:receiver@gmail.com
250 2.1.5 receiver@gmail.com
data
354 Start mail input; end with <CRLF>.<CRLF>
testing email to google output
, yes
.
250 2.6.0 Queued mail for delivery
quit
221 2.0.0 mail.domain.com Service closing transmission channel
Connection closed by foreign host.

For further modification to the configuration you can edit /etc/postfix/main.cf file

~ Sample main.cf configuration ~

#myorigin = /etc/mailname

smtpd_banner = $myhostname ESMTP $mail_name (Ubuntu)
biff = no

# appending .domain is the MUA’s job.
append_dot_mydomain = no

# Uncomment the next line to generate “delayed mail” warnings
#delay_warning_time = 4h

readme_directory = no

# TLS parameters
smtpd_tls_cert_file=/etc/ssl/certs/ssl-cert-snakeoil.pem
smtpd_tls_key_file=/etc/ssl/private/ssl-cert-snakeoil.key
smtpd_use_tls=yes
smtpd_tls_session_cache_database = btree:${data_directory}/smtpd_scache
smtp_tls_session_cache_database = btree:${data_directory}/smtp_scache

# See /usr/share/doc/postfix/TLS_README.gz in the postfix-doc package for
# information on enabling SSL in the smtp client.

myhostname = linuxserver.domain.com
alias_maps = hash:/etc/aliases
alias_database = hash:/etc/aliases
mydestination =
relayhost = mail-server.domain.com
mynetworks = 127.0.0.0/8 172.24.8.0/24
mailbox_size_limit = 0
recipient_delimiter = +
inet_interfaces = loopback-only
inet_protocols = ipv4
myorigin = /etc/mailname

Another way to check if mail is working or not is to use the sendmail program in verbose mode
$ sendmail -v ‘tester@gmail.com’
This is a test email<CRLF>.<CRLF>

Reference:
http://www.rdpslides.com/webresources/FAQ00035.htm
http://pccicla.blogspot.com/2007/02/ubuntu-smtp-server.html

$ apache2 -v

In CentOS, it is

$ httpd -v

To find out where apache2 or httpd program is installed you can do the
$ whereis apache2 or,
$ locate httpd

Wodim stands for Write Data to Optical Disk Media. If you don’t have the software installed in your Ubuntu release do an apt-get

$ apt-get install wodim

To know more about wodim and its parameter definition try man on wodim

To list the CD/DVD devices on the machine, issue

$ wodim –devices

wodim: Overview of accessible drives (2 found) :
————————————————————————-
0 dev=’/dev/scd0′ rwrw– : ‘HL-DT-ST’ ‘CD-RW GCE-8481B’
1 dev=’/dev/scd1′ rwrw– : ‘HL-DT-ST’ ‘DVD-ROM GDR8161B’

Our read-write CD device is in /dev/scd0. So our command for burning the .iso image

$ wodim dev=/dev/scd0 driveropts=burnfree -v -data ubuntu8desktop.iso

To burn audio files

$ wodim dev=/dev/scd0 driveropts=burnfree -v -audio one.wav two.wav three.wav

Further read
i) ubuntu guide http://ubuntuguide.org/wiki/Ubuntu:Feisty/CDDVDBurning

ii) ubuntu site https://help.ubuntu.com/community/CdDvd/Burning

root@myserver:/etc/apache2/conf.d# cat vhosts.conf
NameVirtualHost 192.168.1.100:80

<VirtualHost 192.168.1.100:80>
ServerName cakeapp
DocumentRoot /var/www/cakeapp
</VirtualHost>

(Note that there is no ending forward slash after /var/www/cakeapp. If there had been one, it might cause a problem if the /var/www/cakeapp/app/config/routes.php is not configured correctly indicating a never ending loop in resolving domain name)

root@myserver:/etc/apache2/conf.d# cat /var/www/cakeapp/.htaccess
<IfModule mod_rewrite.c>
RewriteEngine on
RewriteRule ^$ app/webroot/ [L]
RewriteRule (.*) app/webroot/$1 [L]
</IfModule>

Consider the case of two domain names mysite1 and site2 to be served on IP Address 192.168.1.100 (port 80)

Before proceeding let us look at how resolv.conf and hosts file are set up …

$ cat /etc/resolv.conf
search kurinchilion.com
nameserver 192.168.1.100

$ cat /etc/hosts
127.0.0.1 localhost
192.168.1.100 myserver.kurinchilion.com myserver

# The following lines are desirable for IPv6 capable hosts
::1 ip6-localhost ip6-loopback
fe00::0 ip6-localnet
ff00::0 ip6-mcastprefix
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters
ff02::3 ip6-allhosts

We can organize the name server information, directory to serve under each circumstance, folder permission in different ways

i) organize all name server information under /etc/apache2/conf.d/vhosts.conf

NameVirtualHost 192.168.1.100
<VirtualHost 192.168.1.100:80>
ServerName mysite1
DocumentRoot /var/www/mysite1
<Directory /var/www/mysite1>
Options -Indexes FollowSymLinks
AllowOverride All
< </VirtualHost>

<VirtualHost 192.168.1.100:80>
ServerName mysite2
DocumentRoot /home/mysite2
</VirtualHost>

After creating the above file, issue the following commands

$ sudo /etc/init.d/apache2 restart

$ sudo /etc/init.d/apache2 force-reload

ii) have a modular approach to site organization and list separate files based on domain name under /etc/apache2/sites-enabled

File: mysite1
<VirtualHost 192.168.1.100:80>
ServerName mysite1
DocumentRoot /var/www/mysite1

Options FollowSymLinks
AllowOverride All

</VirtualHost>

File: mysite2
<VirtualHost 192.168.1.100:80>
ServerName mysite2
DocumentRoot /home/mysite2
</VirtualHost>

After creating the above files, issue the following commands

$ a2ensite mysite1

$ a2ensite mysite2

(If you want to disable the site configuration, then issue a2dissite sitename)

$ sudo ln -s /etc/apache2/sites-available/mysite1 /etc/apache2/sites-enabled/mysite1

$ sudo /etc/init.d/apache2 force-reload

iii) Organize the same information stated in step (i) but under /etc/apache2/sites-available/default (This already has a symbolic link to /etc/apache2/sites-enabled/000-default)

Virtual Hosting is a technique by which web servers can serve more than one domain name on the same server. It can also be a variation of serving different sites on the same IP but on different ports.

If Ubuntu, you may need to edit
i) /etc/hosts

ii) /etc/apache2/conf.d/vhosts.conf (or /etc/apache2/sites-available/default) depending on how you have configured the virtual host environment

If CentOS, you may need to edit

i) /etc/hosts

ii) /etc/httpd/conf/httpd.conf

For listening to different ports Listen directive should be added to /etc/httpd/conf/httpd.conf file

References:

http://httpd.apache.org/docs/2.0/vhosts/examples.html (Apache’s virtual host configuration documentation)

http://en.wikipedia.org/wiki/Virtual_host

http://apptools.com/phptools/virtualhost.php (For configuring Apache server on Windows)