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.

[general]
bindport = 4569
externip = 99.187.201.22
localnet = 192.168.0.0/255.255.255.0
bindaddr = 0.0.0.0
disallow=all
allow=ulaw
allow=alaw
allow=gsm
allow=ilbc
jitterbuffer=yes
register => NNNNNNNNNN:PPPPPP@201.192.22.232

[voip_provider]
type=friend
username=NNNNNNNNNN
secret=PPPPPP
host=201.192.22.232
context=outgoing

[NNNNNNNNNN]
type=friend
username=NNNNNNNNNN
secret=PPPPPP
host=201.192.22.232
context=incoming
requirecalltoken=auto

[1000]
type=friend
username=1000
host=dynamic
mailbox=1000
secret=1000
context=phones
requirecalltoken=auto

File: extensions.conf

[general]
autofallthrough=yes

[outgoing]
exten => _[1-9].,1,Dial(IAX2/NNNNNNNNNN@201.192.22.232/${EXTEN})
exten => _00.,1,Dial(IAX2/NNNNNNNNNN@201.192.22.232/${EXTEN})
exten => _09XX,1,Dial(IAX2/NNNNNNNNNN@201.192.22.232/${EXTEN})

[internal]
exten => 901,1,VoiceMailMain()
exten => 901,2,Hangup()
exten => 902,1,Meetme(1234,cdM)
exten => 902,2,Hangup()

[incoming]
exten => NNNNNNNNNN,1,Dial(IAX2/1000,20)
exten => NNNNNNNNNN,2,Answer
exten => NNNNNNNNNN,3,Wait(2)
exten => NNNNNNNNNN,4,Set(TIMEOUT(digit)=3)
exten => NNNNNNNNNN,5,Set(TIMEOUT(response)=10)
exten => NNNNNNNNNN,6,Background(conf-usermenu)
exten => 1,1,VoiceMail(1000@internal)
exten => 2,2,MeetMe(1234,cdM)

[phones]
include => internal
include => outgoing

After saving these two files, start up asterisk.
$ asterisk -vvvvgc

The above command will open the asterisk CLI – Command Line Interface

Originally developed for Linux, Asterisk now runs on a variety of operating systems including Solaris, Windows and MacOS.

Environment setup


Asterisk server is configured on a HP dx5150 AMD Athlon, 512 MB RAM, 40 GB machine running CentOS.
Softphones used in the tutorial: Zoiper is used for IAX2 communication and X-Lite for SIP. Both the softphones are configured on Windows XP.

Asterisk: Step by Step
1) Download the asterisk software from asterisk.org. We will be going with the base build and not use other softwares like AsteriskNow or PBXinaFlash for the moment.

2) Setup asterisk repo to ease future upgrades to asterisk
$ cd /etc
$ touch asterisk.repo
$ vi asterisk.repo

[asterisk-tested]
name=CentOS-$releasever – Asterisk – Tested
baseurl=http://packages.asterisk.org/centos/$releasever/tested/$basearch/
enabled=0
gpgcheck=0
#gpgkey=http://packages.asterisk.org/RPM-GPG-KEY-Digium

[asterisk-current]
name=CentOS-$releasever – Asterisk – Current
baseurl=http://packages.asterisk.org/centos/$releasever/current/$basearch/
enabled=1
gpgcheck=0
#gpgkey=http://packages.asterisk.org/RPM-GPG-KEY-Digium

3) Install asterisk on CentOS and start up asterisk
$ yum install asterisk16 asterisk16-configs asterisk16-voicemail libpri

[Source: Check asterisk.org]

To enable auto start of asterisk
$ chkconfig asterisk on

Start/stop/restart asterisk using the commands
$ service asterisk start
$ /etc/init.d/asterisk restart
$ service asterisk stop

To test asterisk service type
$ asterisk -r

4) Register with a VOIP Service provider
To search for the VOIP provider you can use
voip-info.org which has an extensive list of service proivders categorized by region based on different
market segmentation.

Once you have registered with a VOIP Service provider, they will give you
IAX2/SIP Account (your phone number) : NNNNNNNNNN
Account password : PPPPPPPP
IAX2/SIP Server name : myiax.voipprovider.org

So far, we have detailed the environment, setup asterisk on a CentOS server and have registered for an account with a VOIP provider. In the next tutorial, we will see how to configure asterisk settings and to setup an IAX extension for a softphone (soft client) running on windows XP.

Best resources on the internet
asterisk.org http://www.asterisk.org/node
voip-info.org http://www.voip-info.org
asteriskguru.com http://www.asteriskguru.com/

To show users who are logged in to the system
$ who

To show the list of users who have logged in last
$ last

To show the list of all reboots
$ last reboot

To print the content of the last login log from /var/log/lastlog
$ lastlog

$ groupadd www-data
$ useradd -g www-data www-data
$ vi /etc/apache2/apache2.conf

Search for the below lines in apache2.conf,
User root
Group root

and change them to

User www-data
Group www-data

Tip: Sometimes the user group and name will be added to variables within /etc/apache2/envars and may be referenced in /etc/apache2/apache2.conf

Reload apache configuration file setting changes by typing
$ /etc/init.d/apache2 reload

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

Notes for a beginner …
* VMWare Player and VMWare Server are available for free
* A .vmdk file is the virtual hard drive for the guest OS
* A .nvram file stores the BIOS settings of the virtual machine
* A .vmx file stores the configuration settings for the virtual machine. All you
need is a text editor to edit the VMWare configuration settings.
* A .vmsd file stores information about VMWare snapshots.

Some links to get you started in the VMWare’s Virtual World

VMWare Player Download

.vmx creation utilities

EasyVMX (to create virtual machine settings that run on VMWare Player)
VMBuilder

Virtual Machines using VMWare Player – Blogs

Easy to follow Blog on creating virtual machines using .iso image

Create a windows XP virtual machine

Virtual machine repository (Linux distributions)

Linux source

VMWare’s Appliances Listing (There is more to the virtual world than OS)

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

First create a folder in your Windows system, right click the folder and share the folder for network access. Let say that you have created a folder for share as “xpshare” and that the name of your windows machine is “windowsxp” (right click “My Computer” and select properties. Under the tab “Computer Name” you can note the name of the machine)

Now go to your Linux box.

Check the rpm package to ensure if samba, samba client got installed
$ rpm -qa ‘samba*’

If it is not installed, then install it using yum installer
$ yum install samba samba-client

Note the current directory
$ pwd
/tmp

Now issue the samba command to connect to windows box as
$ smbclient //windowsxp/xpshare
password:

Enter the password of your linux box and you will be connected to the windows machine and the command prompt will be changed to

smb: \>

To know the commands that you can use with samba,
smb :\> help
You can use the commands like dir, get, put, chmod, rmdir within the samba share

smb :\> get New File.txt (wrong)
smb :\> get “New File.txt” (correct)

In windows you can easily create and move file with names which has space in it. In order to get a file from windows with spaces, enclose the file name within quotes. Else you will get an error which would state “NT_STATUS_OBJECT_NAME_NOT_FOUND opening remote file \New” as it fails to go beyond the first space in the file name “New File”

smb :\> quit
Now the file “New File.txt” will be in the directory from where you initially connected to the samba share
$ ls -l (to list the file that was brought down from the samba share)

To know the version of samba that you are using , type
$ smbd -V

Premature end of script headers
500 Internal Server Error
The specified CGI application misbehaved by not returning a complete set of HTTP headers.

Some troubleshooting tips:

i) Check /var/log/apache2/error.log (in ubuntu, check the respective apache error log location for the messages)

ii) Check if the content type of the page is correctly set for the html content output.

print “Content-type: text/html\n\n”;

iii) Check if a valid permission has been given for the file to get executed. The file need permission 755 for it to be executed on the server.

iv) Check if the configuration path, inclusion path are set correctly in the referenced programs