Time to edit /etc/hosts file

Unlocking /etc/hosts file

Looking inside of /etc/hosts  - It’s simply a list of names mapped to IP address of every host on the network in order to provide name resolution( name resolution - .

If you have a small host network, easiest way to provide name resolution is by /etc/hosts, which contains the name and address information for important hosts on the local network. This is will be useful when DNS is not running, hosts file has power to override DNS. 

Whenever new host added trick was keeping all those Hosts files up to date, its triggered invention of (BIND) Berkeley Internet Name Domain Server - (DNS) Domain Naming Service to solve this problem

EXAMPLE :

$ vim /etc/hosts

      

# IP_address         canonical_hostname                 [aliases...]

127.0.0.1               localhost.localdomain               localhost

192.168.1.10         bat.mydomain.org                      bat

192.168.1.13         cat.mydomain.org                      cat

146.82.138.7         master.mydomain.org                master

This enables users to access a host by using the alias as an alternative name, Now, you can test "ping bat" or "ping cat.mydomain.org", any of the hosts inside using names instead of its IP address.

Operating System	Location of Hosts File
Windows 9x/Me	c:\windows\hosts
Windows NT/2000	c:\winnt\system32\drivers\etc\hosts
Windows XP/Vista/2003/2008	c:\windows\system32\drivers\etc\hosts
Unix/Linux	/etc/hosts

HOSTNAME - Secrete Key of Linux

Setting up HOSTNAME in Linux

In any network HOSTNAME represents a system for various purpose from application end to mail, web and DB server etc, anything messed up in HOSTNAME service will get disrupted. Learning to re(set) the HOSTNAME very essential key step of any initial troubleshooting or fixing issue.

You should fallow naming conventions while choosing a HOSTNAME in any production site – something more meaningful geographical locations, famous gods, Highest mountain ranges. I would say it like MyProdApp1.shiva.com, MyDbStage.krishna.com, …. So would be easier for anyone to remember.

Only Constraints are -

·      It cannot be longer than 64 characters

·      It can only contain letters, numbers, and dashes

Check your current hostname by using cmd.

# hostname

ProdApp1

FQDN – Fully Qualified Domain Name nothing but your hostname + domain (something.org or anything.com) combined together. 

         

# hostname –f

ProdApp1.himalayan.com

( hostname = ProdApp1  and domainname = himalayan.com )

Five basic Step to get your hostname working fine.

         

STEP1:  

Setting the Hostname Using hostname command

# hostaname –v ProdApp2

Setting hostname to ProdApp2

         

         

STEP2:

Modifying the old hostname

# vi /etc/hostname                              (Debian / Ubuntu)

ProdApp2

Debian has an init script, /etc/init.d/hostname.sh which is called at boot time and sets the hostname what is given in /etc/hostname.

or

sudo service hostname start              

To change the hostname, place only the unqualified hostname in /etc/hostname and run sudo /etc/init.d/hostname.sh

# vi /etc/HOSTNAME                        (SUSE)

ProdApp2

Or

Edit line HOSTNAME="”

# vi /etc/sysconfig/network               (CentOS /RedHat/ Fedora)

         

NETWORKING=yes

HOSTNAME="ProdApp2 "

GATEWAY="192.168.10.10"

GATEWAYDEV="eth0"

FORWARD_IPV4="yes"

STEP 3:

Make new entry /etc/hosts for FQDN resolution.

192.168.10.10                 ProdApp2.himalayan.com                ProdApp2

STEP 4:

Now job would be setting it permanent without any reboot (You won’t get a downtime for just resetting HOSTNAME in Production sites)

#service network restart

Or

#/etc/init.d/network restart

STEP 5:

Checking hostname is set to correct name by using

# hostname –f

ProdApp2.himalayan.com

That’s it – you are done! – Not a big task, but its key task for sure, In STEP 1 command will change the HOSTNAME to new value temporarily.

For Permanent fix, change the configuration file as discussed in STEP 2 & 3 and next time it boots it will read the those configuration file for setting hostname.

ESSENTIALS OF APACHE WEB SERVER

ESSENTIALS OF APACHE WEB SERVER

Apache Web Server Installation Notes

	Install command	Install httpd service boot script start at  boot time Starting  httpd
Fedora / RHEL / Cent OS	# yum install httpd	# chkconfig httpd on # /etc/init.d/httpd start
Debian Linux	# apt-get install apache2	# update-rc.d apache2 defaults # /etc/init.d/apache2 start
Open SUSE	# zypper in apache2 # yast2 -i apache2	# chkconfig --add apache2 # /etc/init.d/apache2 start

Document root location and configuration scripts

	Document root of the default web site	httpd.conf location
Fedora / RHEL / Cent OS	# /var/www/html	# /etc/httpd/conf/httpd.conf
Debian Linux	# /var/www/	# /etc/apache2/apache2.conf # /etc/apache2/ports.conf
Open SUSE	# cd /srv/www/htdocs/	# /etc/apache2/httpd.conf

Compiling and Installing

	Compiling and Installing
Download	# lynx http://httpd.apache.org/download.cgi
Extract	# gzip -d  httpd-2.4.6.tar.gz # tar xvf  httpd-2.4.6.tar.gz # cd  httpd-2.4.6
Configure	# ./configure --prefix= /usr/local/apache2/
Compile	# make
Install	# make install
Customize	# vi /usr/local/apache2/conf/httpd.conf
Test	#  /usr/local/apache2/bin/apachectl -k start

	Other essential details of Apache
server log	/etc/httpd/logs                     à( symbolic link) /var/log/httpd
server modules	/etc/httpd/modules             à( symbolic link) /usr/lib/httpd/modules
server process ID	/var/run                                 à( symbolic link)             /var/run/httpd.pid