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Some Crazy Linux Commands

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 1. If we type mistake at the beginning of the command in terminal would require you to use the slow way of punching the right/left arrow keys to travel in the command string.

Try Ctrl+e to move to the end of the command string and Ctrl+a to reach start. It’s the fastest way to edit a Linux command line. To delete a word in the command string, use Ctrl+w.

2. Another wonder of a simple shell variable is !$.

$ mkdir raj
$ mv raj raj2
$ cd raj2

3. Well, Linux has a shorter and quicker way.

$ mkdir raj
$ mv !$ raj2
$ cd !$

=> here we can use ALT + . or ESC + . Or !$
=> ALT + . and ESC + . print the previous argument
=> !$ points to the last string in the command string

4. What if you want to create a chain of directories and sub-directories, something like /tmp/our/your/mine?

$ mkdir -p /tmp/our/your/mine

P – parent directory

5. One very interesting way to combine some related commands is with &&.

$ cd dir_name && ls -alr && cd ..

6. Have you ever tried checking the vulnerability of your Linux system? Try a fork-bomb to evaluate this:

$ : (){ : |: & };:

It’s actually a shell function; look closely and it’s an unnamed function : () with the body enclosed in {}. The statement ‘:|:’ makes a call to the function itself and pipes the output to another function call—thus we are calling the function twice. & puts all processes in the background and hence you can’t kill any process. Finally ‘;’ completes the function definition and the last ‘:’ initiates a call to this unnamed function. So it recursively creates processes and eventually your system will hang. This is one of the most dangerous Linux commands and may cause your computer to crash!

 How to avoid a fork bomb? Of course, by limiting the process limit; you need to edit /etc/security/limits.conf. Edit the variable nproc to user_name hard nproc 100. You require root privileges to modify this file.

7. One more dirty way to hack into the system is through continuous reboots, resulting in the total breakdown of a Linux machine. Here’s an option that you need root access for. Edit the file /etc/inittab and modify the line id:5:initdefault: to id:6:initdefault:. That’s all! Linux specifies various user modes and 6 is intended for reboot. Hence, your machine keeps on rebooting every time it checks for the default user mode.
check – Modify your Grub configuration (the Linux bootloader) and boot in single user mode. Edit the file /etc/inittab and change the default user level to 5.

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Linux

How To Recover The Lost Or Deleted Partitions In Linux

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This article explain you how to recover the lost or deleted partition in linux. Losing of disk partition is occur due to sudden power off or some other problem like accidently deleting the hard disk partition by the users. In this cases, if you want to recover the losted disk partition their is so many recovering tools are availble on linux. In this article we will use the gpart to recover the disk partition.

The gpart is guess PC-type hard disk partitions, that tries to recover the hard disk partitions. This gpart have limitation, It can only detect the following type of partitions.

 

* beos

* bsddl

* ext2

* fat

* hpfs

* hmlvm

* lswap

* minix

* ntfs

* qnx4

* rfs

* s86dl

* xfs

To add more filesystem for guessing, modules can be added at runtime

 

 Step 1

To recover the lost or deleted partition of your hard disk, first boot the system with a linux OS CD that what flavour you used in that crashed disk finally.

 

Step 2

Then go to rescue mode with that Linux OS CD, that bring you to a rescue mode .

 

Step 3

Now you put the following command for available disk partition checking

 

# fdisk -l

Disk /dev/sda: 160.0 GB, 160041885696 bytes

18 heads, 4 sectors/track, 4341414 cylinders

Units = cylinders of 72 * 512 = 36864 bytes

 

Device Boot Start End Blocks Id System

This show no partition on your disk, it means all the partiotions are losted.

 

Step 4

Now run the below command

 

# gpart /dev/sda

The output of the above command will be like this

This command will show’s the all guessed partitions available on the hard disk. Now verify the result that showing the lost partition of your disk correctly or not.

 

Step 5

After verifying the output write the the partition table by using the -W option on gpart command

 

# gpart  -W  /dev/sda  /dev/sda

 

it can be written the guessed disk partition to the specified file or device on your hard disk. now you got back your deleted partition successfully .

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Linux

Basics Of Network File Sharing Setup on Linux

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Introduction:

Network File Sharing (NFS) is a protocol which used to share the local hard disk Between the Linux machines over the network, that act as a local disk to the clent user.

 

 Versions:

 

At present there are three versions of NFS

 

* NFSv2 – It is a older and is widely supported version

 

* NFSv3 – It supports safe asynchronous writes and a more robust error handling than NFSv2,it also supports 64-bit file sizes and offsets

 

* NFSv4 – It works through firewalls and on the Internet, no longer requires an rpcbind service, supports ACLs, and utilizes stateful operations

 

 

Port Number :

 

The Default Port Number of NFS is 2049 

 

 

Packages Needed:

 

The Packages needed for NFS are

 

* nfs-utils

 

* portmap

 

* nfs4-acl-tools

 

Required Services:

To run the NFS the following dameon or services is used

* portmap (rpcbind for RHEL 6)

* nfslock

* nfs

 

Portmap :

portmap or RPC Program or otherwise called as rpcbind.NFS uses Remote Procedure Calls (RPC) to handle the requests between clients and servers.

 

nfslock :

It lock the files for remote and local nfs request .

 

nfs :

service nfs start the NFS server and the appropriate RPC processes to service requests for shared NFS file systems.

 

Configuring NFS on the Server :

Both the NFS server and NFS client need the NFS package installed and running on the machine. The server needs rpcbind, nfs, and nfslock operational, as well as a correctly configured /etc/exports file.The /etc/exports file is the main NFS configuration file, and it consists of two columns. The first column lists the sharing directories over the network. The second column has two parts. The first part is for mentioning the networks or DNS domains that can get access to the directory, and the second part is for NFS options in brackets.

 

Example:

 

# vim /etc/exports

 

/home/example/share          192.168.1.2 (ro,sync)

 

:wq

 

Then Start the Required services

 

Configuring NFS on The Client :

NFS configuration on the client requires you to start the NFS application; create a directory on which to mount the NFS server’s directories that you exported via the /etc/exports file, and finally to mount the NFS server’s directory on your local directory, or mount point.

 

 /etc/fstab file

 

The /etc/fstab file lists all the partitions that need to be mounted automatically when the system boots. For this, we need to edit the /etc/fstab file if you need the NFS directory to be made permanently available to the users .

 

A valid /etc/fstab entry to mount an NFS export should contain the following information:

 

server:/remote-shaing-path/ /local-mounting-directory/ nfs options 0 0

 

Example:

 

# vim /etc/fstab

 

192.168.1.2:/home/example/sharing  /home/example2/remote-files  nfs  soft,nfsvers=2  0  0

:wq

 

Possible NFS Mount Options

 

bg   ==========>   Retry mounting in the background if mounting initially fails

 

fg   ==========>   Mount in the foreground

 

soft   ==========>   Use soft mounting

 

hard   ==========>   Use hard mounting

 

rsize=n   ==========>   The amount of data NFS will attempt to access per read operation. The default is dependent on the kernel. For NFS version 2, set it to 8192 to assure maximum throughput.

 

wsize=n   ==========>   The amount of data NFS will attempt to access per write operation. The default is dependent on the kernel. For NFS version 2, set it to 8192 to assure maximum throughput.

 

nfsvers=n   ==========>   The version of NFS the mount command should attempt to use

 

tcp   ==========>   Attempt to mount the filesystem using TCP packets: the default is UDP.

 

intr   ==========>   If the filesystem is hard mounted and the mount times out, allow for the process to be aborted using the usual methods such as CTRL-C and the kill command.

 

 

Temprovary Mount of NFS :

 

mount -t nfs [SERVER:sharing-path] [mounting-directory]

 

Example : #  mount -t nfs 192.168.1.2:/home/example/sharing /mnt/

 

( -t indicates the file system type )

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Linux

Unix/Linux command prompt keyboard shortcut keys

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Linux / Unix Command prompt supports huge number of shortcut keys. If you familiar with the shortcut keys you can utilizes the command prompt very faster. The more practice on the shortcut keys will give you more speed in the command prompt. Below are the shortcut keys.

 

To move cursor one word backword

 

esc  +b

 

To move cursor one word forward

 

esc  +f

 

To move cursor to the starting of the line

 

ctrl +a

 

To move cursor one letter backword

 

ctrl +b

 

Terminate foreground job

 

ctrl +c

 

To Logout of the terminal

 

crrl +d

 

To move cursor to the end of the line

 

ctrl +e

 

To move cursor forward

 

ctrl +f

 

To delete one letter backward like backspace

 

ctrl +h

 

To delete contents from where the pointer to left side end

 

ctrl +u

To delete contents from where the pointer to Right side end.

 

ctrl +k

 

To delete one word from where the pointer to one word on left side

crtl +w

 

To move cursor one letter forward

 

ctrl +f

 

To display the previously executed Command

 

ctrl +p

 

To display the next command when ctrl +p is used

 

ctrl +n

 

To Clear the screen

ctrl +l

 

To execute a command like hitting ENTER

ctrl +j

 

To execute a command like hitting ENTER

 

ctrl +o

 

To pastes text previously erased (with Ctl-U or Ctl-W)

 

ctrl  +Y

 

Short cut key to reverse search in the command history

 

ctrl +r

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