The Linux Juggernaut

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Today I found some interesting hack about Mozilla/Firefox. I am in need of java in my Ubuntu machine. I have installed java, but I am not able to see any java related sites in my browser So when I have started searching for related topics, I found my answer how to check java is configured in your browser or not. I came to know about Firefox hidden “about protocol”. Though my browser is showing java enabled, but I am not able to see java content of site. The solution for this is to check whether java is configured properly to your browser or not.

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Webmin is a web based administration tool to do daily admin activities.
by using this tool we can configure.
1. User management
2. Disk management such as RAID, LVM etc.
3. Disk Quotas
4. Services/Servers such as apache, DNS, PHP, Mysql etc
5. Will allow us to confgire/controll many systems through single interface(ie through a web browser).

For example you want to controle your linux machine remotly through no Linux machines such as windows or a mobile device. We can do the system admin activity through a web broswer. Some time I used to login to my linux server which is located in SJ, USA through my Sonyerricson C702 mobile phone to take backups.

Installation in Ubuntu
If you like to install and update Webmin via APT, edit the /etc/apt/sources.list file on your system and add the line :
deb http://download.webmin.com/download/repository sarge contrib
You should also fetch and install a GPG key with which the repository is signed, with the

Commands :
cd /root
wget http://www.webmin.com/jcameron-key.asc
apt-key add jcameron-key.asc
You will now be able to install with the commands :
apt-get update
apt-get install

Installation in Redhat/Fedora
#yum install perl
#yum install webmin

After installation webmin server will work on localhost at 10000 port, which is default port for webmin.

To access webmin through your browser
http://localhost:10000

Why a unix admin should know about Webmin?
Ans : Webmin is a one stop to administer your machine we can manage allmost all the servers, disk management, user management etc. Which is supported on different operating systems, recently it is supporting Windows too(with limitations) .

Which are the operating systems we can install webmin to administer the system?
Ans : Bcz it is supported in many unix and linux flavors such as
1. Redhat, Fedora, SuSE and Mandrake through RPM packages
2. Debian and Ubuntu through .deb packages
3. HPUX, FreeBSD and Slackware Linux through source code(eg: .tar.gz and .tar.bz)
4. MS Windows through exe

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Its long time back I have learnt Heartbeat clustering around March-2008, but still this point I never implemented for production servers. This is my first attempt to do it and I am successful in implementing it for two node fail-over Cluster. Clustering is very complex and very advanced topic which I cannot deal with in one post. In this post I will give you some basics of Clustering, advantages of Clustering and configuration of simple fail-over Cluster.
Let’s start.
What is a Cluster any way?
Ans : A computer cluster is a group of linked computers, working together closely so that in many respects they form a single computer. The components of a cluster are commonly, but not always, connected to each other through fast local area networks. Clusters are usually deployed to improve performance and/or availability over that of a single computer, while typically being much more cost-effective than single computers of comparable speed or availability – www.wikipedia.org .
Cluster terminology.

Node : It’s one of the system/computer which participates with other systems to form a Cluster.

Heartbeat : This a pulse kind of single which is send from all the nodes at regular intervals using a UDP packet so that each system will come to know the status of availability of other node. It’s a kind of door knocking activity like pinging a system, So that each node which are participating in Cluster will come to know the status of other nodes availability in the Cluster.

Floating IP or Virtual IP : This is the IP assigned to the Cluster through which user can access the services. So when ever clients request a service they will be arrived to this IP, and client will not know what are the back-end/actual ip addresses of the nodes. This virtual IP is used to nullify the effect of nodes going down.

Master node : This is the node most of the time where services are run in a High availability Cluster.

Slave node : This is the node which is used in High availability Cluster when master node is down. It will take over the role of servicing the users, when it will not receive heartbeat pulse from master. And automatically gives back the control when the master server is up and running. This slave comes to know about the status of master through heartbeat pulse/signals.

Types of Clusters:
Cluster types can be divided in to two main types
1. High availability :
These types of Clusters are configured where there should be no downtime. If one node in the cluster goes down second node will take care of serving users without interrupted service with availability of five nines i.e. 99.999%.

2. Load balancing :
These types of Clusters are configured where there are high loads from users. Advantages of load balancing are that users will not get any delays in their request because load on a single system is shared by two or more nodes in the Cluster.

Advantages of Cluster :
1.Reduced Cost : Its cheaper to by 10 normal servers and do cluster on them then buying a high end servers like blade servers, which will do more work than a single blade server which have more processing power.
2. Processing Power
3. Scalability
4. Availability

Configuration files details :
Three main configuration files :
· /etc/ha.d/authkeys
· /etc/ha.d/ha.cf
· /etc/ha.d/haresources

Some other configuration files/foldersto know :
/etc/ha.d/resource.d. Files in this directory are very important which contains scripts to start/stop/restart a service run by this Heartbeat cluster.

Before configuration of Heartbeat Cluster these below points to be noted.

Note1 : The contents of ha.cf file are same in all the nodes in a cluster, except ucast and bcast derivatives.

Note2 : The contents of authkeys and haresources files are exact replica on all the nodes in a cluster.

Note3 : A cluster is used to provided a service with high availability/high performance, that service may be a web server, reverse proxy or a Database.

Test scenario setup:
1. The cluster configuration which I am going to show is a two node cluster with failover capability for a Squid reverse proxy..
2.For Squid reverse proxy configuration please click here..
3. Node details are as follows

Node1 :
IpAddress(eth0):10.77.225.21
Subnetmask(eth0):255.0.0.0
Default Gateway(eth0):10.0.0.1
IpAddress(eth1):192.168.0.1(To send heartbeat signals to other nodes)
Sub net mask (eth1):255.255.255.0
Default Gateway (eth1):None(don’t specify any thing, leave blank for this interface default gateway).

Node2 :
IpAddress(eth0):10.77.225.22
Subnetmask(eth0):255.0.0.0
Default Gateway (eth0):10.0.0.1
IpAddress(eth1):192.168.0.2(To send heartbeat signals to other nodes)
Sub net mask (eth1):255.255.255.0
Default Gateway(eth1):None(don’t specify any thing, leave blank for this interface default gateway).

4. Floating Ip address:10.77.225.20

Lets start configuration of Heartbeat cluster. And make a note that ever step in this Heartbeat cluster configuration is divided in two parts parts
1.(configurations on node1)
2.(configurations on node2)

For better understanding purpose

Step1 : Install the following packages in the same order which is shown

Step1(a) : Install the following packages on node1
#rpm -ivh heartbeat-2.1.2-2.i386.rpm
#rpm -ivh heartbeat-ldirectord-2.1.2-2.i386.rpm
#rpm -ivh heartbeat-pils-2.1.2-2.i386.rpm
#rpm -ivh heartbeat-stonith-2.1.2-2.i386.rpm

Step1(b) : Install the following packages on node2
#rpm -ivh heartbeat-2.1.2-2.i386.rpm
#rpm -ivh heartbeat-ldirectord-2.1.2-2.i386.rpm
#rpm -ivh heartbeat-pils-2.1.2-2.i386.rpm
#rpm -ivh heartbeat-stonith-2.1.2-2.i386.rpm


Step2 : By default the main configuration files (ha.cf, haresources and authkeys) are not present in /etc/ha.d/ folder we have to copy these three files from /usr/share/doc/heartbeat-2.1.2 to /etc/ha.d/

Step2(a) : Copy main configuration files from /usr/share/doc/heartbeat-2.1.2 to /etc/ha.d/ on node 1
#cp /usr/share/doc/heartbeat-2.1.2/ha.cf /etc/ha.d/
#cp /usr/share/doc/heartbeat-2.1.2/haresources /etc/ha.d/
#cp /usr/share/doc/heartbeat-2.1.2/authkeys /etc/ha.d/

Step2(b) : Copy main configuration files from /usr/share/doc/heartbeat-2.1.2 to /etc/ha.d/ on node 2
#cp /usr/share/doc/heartbeat-2.1.2/ha.cf /etc/ha.d/
#cp /usr/share/doc/heartbeat-2.1.2/haresources /etc/ha.d/
#cp /usr/share/doc/heartbeat-2.1.2/authkeys /etc/ha.d/


Step3 : Edit ha.cf file
#vi /etc/ha.d/ha.cf

Step3(a) : Edit ha.cf file as follows on node1
debugfile /var/log/ha-debug
logfile /var/log/ha-log
logfacility local0
keepalive 2
deadtime 25
warntime 10
initdead 50
udpport 694
bcast eth1
ucast eth1 192.168.0.1
auto_failback on
node rp1.linuxnix.com
node rp2.linuxnix.com

Step3(b) : Edit ha.cf file as follows on node2
debugfile /var/log/ha-debug
logfile /var/log/ha-log
logfacility local0
keepalive 2
deadtime 25
warntime 10
initdead 50
udpport 694
bcast eth1
ucast eth1 192.168.0.2
auto_failback on
node rp1.linuxnix.com
node rp2.linuxnix.com

Let me explain each entry in detail:
Debugfile : This is the file where debug info with good details for your heartbeat cluster will be stored, which is very much useful to do any kind of troubleshooting.

Logfile : This is the file where general logging of heartbeat cluster takes place.

Logfacility : This directive is used to specify where to log your heartbeat logs(if its local that indicates store logs locally or if it’s a syslog then store it on remote server and none to disable logging). And there are so many other options, please explore yourself.

Keepalive : This directive is used to set the time interval between heartbeat packets and the nodes to check the availability of other nodes. In this example I specified it as two seconds(keepalive 2).

Deadtime : A node is said to be dead if the other node didn’t receive any update form it.

Warntime : Time in seconds before issuing a "late heartbeat" warning in the logs.

Initdead : With some configurations, the network takes some time to start working after a reboot. This is a separate "deadtime" to handle that case. It should be at least twice the normal deadtime.

Udpport : This is the port used by heartbeat to send heartbeat packet/signals to other nodes to check availability(here in this example I used default port:694).

Bcast : Used to specify on which device/interface to broadcast the heartbeat packets.

Ucast : Used to specify on which device/interface to unicast the heartbeat packets.

auto_failback : This option determines whether a resource will automatically fail back to its "primary" node, or remain on whatever node is serving it until that node fails, or an administrator intervenes. In my example I have given as on that indicate if the failed node come back online, controle will be given to this node automatically. Let me put it in this way. I have two nodes node1 and node2. My node one machine is a high end one and node is for serving temporary purpose when node 1 goes down. Suppose node1 goes down, node2 will take the control and serve the service, and it will check periodically for node1 starts once it find that node 1 is up, the control is given to node1.

Node : This is used to specify the participated nodes in the cluster. In my cluster only two nodes are participating (rp1 and rp2) so just specify that entries. If in your implementation more nodes are participating please specify all the nodes.


Step4 : Edit haresources file
#vi /etc/ha.d/haresources

Step4(a) : Just specify below entry in last line of this file on node1
rp1.linuxnix.com 10.77.225.20 squid

Step4(b) : Just specify below entry in last line of this file on node1
rp1.linuxnix.com 10.77.225.20 squid

Explanation of each entry :
rp1.linuxnix.com is the main node in the cluster
10.77.225.20 is the floating ip address of this cluster.

Squid : This is the service offered by the cluster. And make a note that this is the script file located in /etc/ha.d/ resource.d/.

Note : By default squid script file will not be there in that folder, I created it according to my squid configuration.

What actually this script file contains?
Ans : This is just a start/stop/restart script for the particular service. So that heartbeat cluster will take care of the starting/stoping/restarting of the service(here its squid).
Here is what squid script file contains.
http://sites.google.com/site/surendra/Home/squid.txt.txt?attredirects=0&d=1

Step5 : Edit authkeys file, he authkeys configuration file contains information for Heartbeat to use when authenticating cluster members. It cannot be readable or writeable by anyone other than root. so change the permissions of the file to 600 on both the nodes..

Two lines are required in the authkeys file:
A line which says which key to use in signing outgoing packets.
One or more lines defining how incoming packets might be being signed.

Step5 (a) : Edit authkeys file on node1
#vi /etc/ha.d/authkeys
auth 2
#1 crc
2 sha1 HI!
#3 md5 Hello!
Now save and exit the file

Step5 (b) : Edit authkeys file on node2
#vi /etc/ha.d/authkeys
auth 2
#1 crc
2 sha1 HI!
#3 md5 Hello!
Now save and exit the file


Step6 : Edit /etc/hosts file to give entries of hostnames for the nodes


Step6(a) : Edit /etc/hosts file on node1 as below

Step6(b) : Edit /etc/hosts file on node2 as below
10.77.225.22 rp2.linuxnix.com rp2

Step7 : Start Heartbeat cluster

Step7(a) : Start heartbeat cluster on node1
#service heartbeat start

Step7(b) : Start heartbeat cluster on node2
#service heartbeat start

Checking your Heartbeat cluster:
If your heartbeat cluster is running fine a Virtual Ethernet Interface is created on node1 and 10.77.225.20
Clipped output of my first node
# ifconfig

Eth0 Link encap:Ethernet HWaddr 00:02:A5:4C:AF:8E
inet addr:10.77.225.21 Bcast:10.77.231.255 Mask:255.255.248.0
inet6 addr: fe80::202:a5ff:fe4c:af8e/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:5714248 errors:0 dropped:0 overruns:0 frame:0
TX packets:19796 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:1533278899 (1.4 GiB) TX bytes:4275200 (4.0 MiB)
Base address:0x5000 Memory:f7fe0000-f8000000

Eth0:0 Link encap:Ethernet HWaddr 00:02:A5:4C:AF:8E
inet addr:10.77.225.20 Bcast:10.77.231.255 Mask:255.255.248.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
Base address:0x5000 Memory:f7fe0000-f8000000

Eth1 Link encap:Ethernet HWaddr 00:02:A5:4C:AF:8F
inet addr:192.168.0.1 Bcast:192.168.0.255 Mask:255.255.255.0
inet6 addr: fe80::202:a5ff:fe4c:af8f/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:145979 errors:0 dropped:0 overruns:0 frame:0
TX packets:103753 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:100
RX bytes:38966724 (37.1 MiB) TX bytes:27640765 (26.3 MiB)
Base address:0x5040 Memory:f7f60000-f7f80000

Try accessing your browser whether Squid is working fine or not. Please follow up comming posts how to troubleshoot heartbeat cluster.

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How to view/list only directories in Linux?
Ans : This can be achieved in two ways
1. Through ls command
2. Through find command

With ls we have to use grep to get the directory listings.
Ls –l grep ^d

Example :
[root@test surendra_a]# ls -l grep ^d
d--------- 2 surendra_a surendra_a 4096 Sep 8 09:54 HTWFAIP
drwxrwxr-x 2 surendra_a root 4096 Nov 27 12:30 LinuxCBT - RHEL5
drwxrwxr-x 2 surendra_a root 4096 Oct 12 16:40 Software
[root@test surendra_a]#

With find we can have more controle on how to display only directories.

A. To display all the directories and sub-directories in present directory
#find . -type d

B. Displaying only directories in present directory
#find /root/ -type d –maxdepth 1

C. Displaying just directories in present directry and its sub-directories
#find /root/ -type d –maxdepth 2

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How to mount NFS(Network File System) on a Local Ubuntu?
Ans : As Ubuntu will not install most of the tools by default. In that NFS tool is also one.

When you try to mount NFS share using mount command, with out a client you will get the following error
mount -t nfs v-itig41:/var/data /mnt
mount: wrong fs type, bad option, bad superblock on v-itig41:/var/data,
missing codepage or helper program, or other error
(for several filesystems (e.g. nfs, cifs) you might
need a /sbin/mount. helper program)
In some cases useful info is found in syslog - try
dmesg tail or so

So in order to mount NFS share in Ubuntu you require following packages.
1. portmap
2. nfs-common

Just install above two packages
#apt-get install portmap
#apt-get install nfs-common
or
#apt-get install portmap nfs-common
Reading package lists. Done
Building dependency tree
Reading state information. Done

The following extra packages will be installed:
libgssglue1 libnfsidmap2 librpcsecgss3

The following NEW packages will be installed:
libgssglue1 libnfsidmap2 librpcsecgss3 nfs-common portmap
0 upgraded, 5 newly installed, 0 to remove and 192 not upgraded.
Need to get 333kB of archives.
After this operation, 1,126kB of additional disk space will be used.
Do you want to continue [Y/n]? y
Get:1 http://archive.ubuntu.com karmic/main libgssglue1 0.1-3 [23.6kB]
Get:2 http://archive.ubuntu.com karmic/main libnfsidmap2 0.21-2 [28.4kB]
Get:3 http://archive.ubuntu.com karmic/main librpcsecgss3 0.18-1 [32.4kB]
Get:4 http://archive.ubuntu.com karmic/main portmap 6.0-10ubuntu2 [37.4kB]
Get:5 http://archive.ubuntu.com karmic/main nfs-common 1:1.2.0-2ubuntu8 [211kB]
Fetched 333kB in 4s (80.6kB/s)
Preconfiguring packages ...
Selecting previously deselected package libgssglue1.
(Reading database ... 122969 files and directories currently installed.)
Unpacking libgssglue1 (from .../libgssglue1_0.1-3_i386.deb) ...
Selecting previously deselected package libnfsidmap2.
Unpacking libnfsidmap2 (from .../libnfsidmap2_0.21-2_i386.deb) ...
Selecting previously deselected package librpcsecgss3.
Unpacking librpcsecgss3 (from .../librpcsecgss3_0.18-1_i386.deb) ...
Selecting previously deselected package portmap.
Unpacking portmap (from .../portmap_6.0-10ubuntu2_i386.deb) ...
Selecting previously deselected package nfs-common.
Unpacking nfs-common (from .../nfs-common_1%3a1.2.0-2ubuntu8_i386.deb) ...
Processing triggers for man-db ...
Processing triggers for sreadahead ...
Setting up libgssglue1 (0.1-3) ...
Setting up libnfsidmap2 (0.21-2) ...
Setting up librpcsecgss3 (0.18-1) ...
Setting up portmap (6.0-10ubuntu2) ...
portmap start/running, process 4690
Setting up nfs-common (1:1.2.0-2ubuntu8) ...
Creating config file /etc/idmapd.conf with new version
Creating config file /etc/default/nfs-common with new version
Adding system user `statd' (UID 115) ...
Adding new user `statd' (UID 115) with group `nogroup' ...
Not creating home directory `/var/lib/nfs'.
statd start/running, process 4912
gssd stop/pre-start, process 4937
idmapd stop/pre-start, process 4965
Processing triggers for libc-bin ...
lpconfig deferred processing now taking place
And there is no need to start/restart any service. Just try to mount your nfs share
mount -t nfs v-itig41:/var/data /mnt
root@ps6061:/etc/apache2#
now change the directory to /mnt and check your files
or
give
#cat /etc/mtab
This command will show your nfs mount share.

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I have a system with two Lan cards
Eth0 is assigned with 10.22.33.21 IP address and default gateway is 10.22.33.1
Eth1 is assigned with 192.168.0.1 IP address and default gateway is 192.168.0.100
Now the system communicate with any system in these networks(10.22.33.0 and 192.168.0.0). The answer is no.
Never try to assign multiple gateways to a system if it have more than one LAN card.
Just assign a single gateway for effective communication.

So in this example we can have two scenarios:
Either you can assign Eth0 10.22.33.21 IP address with default gateway as 10.22.33.1 and Eth1 should have just an IP 192.168.0.1 no default gate for this Eth1 interface

Or

Eth0 10.22.33.21 IP address without default gateway and Eth1 IP address 192.168.0.1 with default gateway as 192.168.0.100.

You may get doubt if I assign multiple default gateways what will happen?
Ans : You cannot communicate/ping properly to other networks. If you want to try this out try on a test network and feel the difference.

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How to install and configure the Thunderbird and add lightning extention to the calender ?
Ans : Thunderbird is an excelent e-mail client known in open source world other popular e-mail client is evolution. As of this writing TB3 is still in beta phase so we will see how to install Thunderbird 2.0.0.23 on Ubuntu 9.10.

Step1 : Edit the source list to point the mozilla reposatory and add the below mention reposatories at the end of the file.
#gedit /etc/apt/sources.list
deb http://ppa.launchpad.net/ubuntu-mozilla-daily/ppa/ubuntu karmic main
deb-src http://ppa.launchpad.net/ubuntu-mozilla-daily/ppa/ubuntu karmic main
save and exit the file

Step2 : Update the reposatory list, that your system knows from where we should download thunderbird and install it
#apt-get update

Step3 : Now install mozilla with apt-get command
#apt-get install mozilla-thunderbird
Reading package lists. Done
Building dependency tree
Reading state information. Done

The following extra packages will be installed:
thunderbird
Suggested packages:
thunderbird-gnome-support

The following NEW packages will be installed:
mozilla-thunderbird thunderbird
0 upgraded, 2 newly installed, 0 to remove and 192 not upgraded.
Need to get 12.2MB of archives.
After this operation, 36.3MB of additional disk space will be used.
Do you want to continue [Y/n]? y

Get : 1 http://archive.ubuntu.com karmic/main thunderbird 2.0.0.23+build1+nobinonly-0ubuntu1 [12.1MB]

Get : 2 http://archive.ubuntu.com karmic/main mozilla-thunderbird 2.0.0.23+build1+nobinonly-0ubuntu1 [62.0kB]
Fetched 12.2MB in 1min 52s (108kB/s)
Selecting previously deselected package thunderbird.
(Reading database ... 114241 files and directories currently installed.)
Unpacking thunderbird (from .../thunderbird_2.0.0.23+build1+nobinonly-0ubuntu1_i386.deb) ...
Selecting previously deselected package mozilla-thunderbird.
Unpacking mozilla-thunderbird (from .../mozilla-thunderbird_2.0.0.23+build1+nobinonly-0ubuntu1_all.deb) ...
Processing triggers for man-db ...
Processing triggers for desktop-file-utils ...
Setting up thunderbird (2.0.0.23+build1+nobinonly-0ubuntu1) ...
Setting up mozilla-thunderbird (2.0.0.23+build1+nobinonly-0ubuntu1) ...
Processing triggers for libc-bin ...
ldconfig deferred processing now taking place

Step4 : To access newly installed Thunderbird go to Applications--> Internet --> Mozilla thunderbird mail.

Step5 : Now configure and add the lightning extention for getting calender.

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In most of the linux machins terminal option will be there on right clicking on desktop. But strangely in Ubuntu there is no such fecility.

For admins/power users who are using linux require terminal/console access with easy. So in this post i will show you how to right click terminal option in ubuntu. Just execute below command you terminal is there on your right click of the mouse.
apt-get install nautilus-open-terminal
Once this installed try to check if you are able to get terminal option on right clicking on desktop, if you didnot get any such option just restart the machine and check. You will get the terminal option.

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I thought of writing a post on some good comamnds which are capable of running on other commands.

With my knowledge i tried to gather below commands, please share your thoughts/experiences through comments.

1.strace -- very much handy when debugging a command/script which will struck in middle of execution. This command will be tough when you start using it initially, but will come hand when start using excessively. And there are some more sister commands for this ie ltrace mtrace which i never used, please give some inputs on these.

For example if we want to see how ls command is executed and want to see what actually ls command is doing? you can check that out by using strace
#strace ls

2.watch --used to see a command executino at a regular intervels(by default 2 sec)

Some valuable examples

a.Monitoring a copy activity of CD/DVD, which will show the progress.
#cp -ar /dev/cdrom /mnt &
#watch ls -l /mnt

b.Watching who are connecting to a system and disconnecting
#watch lsof -i

3.time --To see how much time a command taken to execute, This a handy tool when you want to check how much time your shell script taken to execute.
#time ls
#time shellscript.sh

4.whereis --to find where a command located
#whereis ls

5.whatis --to get one line info on a command
#whatis ls

And a well known man command and info commands to see the details of a command what it can do.
#man ls
#info ls

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By default in Ubuntu SSH(Secure SHell) server is not installed. This is a big problem when you want to access the Ubuntu machines from other machines we can not access. In this post I will show you how to install and SSH server and give you some examples how to use ssh.

Installing ssh server in ubuntu
#apt-get install openssh-server
Once you install now try to login to that machine
#ssh 0

Note : In this example i am login to same machine, which i am going to check whether service is running or not. We should get successfully login for the above command which will prompt for password.

SSH examples:

Example1 : Login to a remote machine using its hostname
#ssh servername

Note : This will allow us to login to remote server on default ssh port(22)

Example2 : Login to a remote machine using its IP add
#ssh 192.168.0.1

Example3 : Login in to a remote machine which uses different port for running ssh server
#ssh 192.168.0.1 2010

Note : Here SSH server is running on 2010 port(some times this is good practice to secure the system).

Example4 : Login to a remote machine with different user
#ssh user@192.168.0.1

Example5 : Executing commands on remote machine with out login to the machine.
#ssh 192.168.0.1 "ls -l"

Note : This command will execute "ls -l" command on remote host:192.168.0.1 and gives the output on a local machine.

SSH server is a big concept which can not be dealt with in one post. Will try to write another post on SSH server.

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How to mount NTFS(New Technology File System) partations in Linux?
Ans : By default we can not mount ntfs partations, to do that we have two options
1.Compiling kernle, click here to see how to compile a kernel.
2.Install Fuse tool and then mount the ntfs partation's.

Let us start how to install fuse and then mount ntfs partations
Step1 : Install the following softwares
#yum install fuse
#yum install dkms-fuse
#yum install fuse-ntfs-3g

If you dont have yum and want to install through rpm, then you have to download the above three packages and install them through rpm command.
For this you need to download correct versions of above packages from dag weirs repository.

Repository link is as following:
http://dag.wieers.com/rpm/packages/

Step2 : After installing above packages, you need to ensure that "fuse" module is loaded or not, run the below command
#lsmod grep fuse

Step3 : If this is not showing any thing, we have to load this fuse module.
#modprobe fuse

Step4 : After loading fuse module, run following command to mount ntfs filesystem in linux system
# mount -t ntfs-3g /dev/hdb1 /media
Above command will mount ntfs partition in R/W mode.

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