Establishing ssh key pair when “Host key verification failed”

Somtime you will get like following you try to other system via SSH

$ ssh root@192.168.1.1
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
@    WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED!     @
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY!
Someone could be eavesdropping on you right now (man-in-the-middle attack)!
It is also possible that the RSA host key has just been changed.The fingerprint for
the RSA key sent by the remote host is 3f:1b:f4:bd:c5:aa:c1:1f:bf:4e:2e:cf:53:fa:d8:59.
Please contact your system administrator.Add correct host key in
 /home/guest/.ssh/known_hosts to get rid of this message.Offending key in /home/guest/.ssh/known_hosts:3 RSA host key for 192.168.1.1has changed and you have requested strict checking.Host key verification failed.

It's simple error.Just you remove that unknown host.Then that will work fine

            "ssh-keygen -R hostname"
           
This deletes the offending key from the known_hosts or open it up and delete the entry for the offending ip/hostname

Example:

            "rm -f /home/user/.ssh/known_hosts"

Restrict Root SSH Login on Linux

One of the biggest security holes you could open on your server is to allow directly logging in as root through ssh.

We can Disable Root SSH Login, we’ll need to edit the sshd_config file, which is the main configuration file for the sshd service. The location will sometimes be different, but it’s usually in /etc/ssh/. Open the file up while logged on as root.

  " vi /etc/ssh/sshd_config "

Find this section in the file, containing the line with “PermitRootLogin” in it.

    #LoginGraceTime 2m
    #PermitRootLogin no
    #StrictModes yes
    #MaxAuthTries 6

Make the line look like this to disable logging in through ssh as root.

    PermitRootLogin no

Now you’ll need to restart the sshd service:

  " /etc/init.d/sshd restart "

Difference and Usage between .toString , String.valueOf() , (String)

OBJECT.toString() calls the object's toString() method. It cannot be used for primitives, and it will give NullPointerException if OBJECT is null.

String.valueOf(OBJECT) will call the object's toString() method if OBJECT is a non-null reference. If OBJECT is a null reference, it will return the string "null". If OBJECT is a primitive, it will return a String representation of that primitive, probably by calling toString on an appropriate wrapper object, or a static String.valueOf method on the appropriate wrapper class.

Both toString() and String.valueOf are just methods. There's nothing special about them. You can look at their docs and/or source code to see what they do.

(String)OBJECT will attempt to cast the reference OBJECT to a String. I doesn't change the object in any way. If OBJECT is not a reference to one of String's supertypes--Object, Comparable, etc.Then it will be a compile-time error. If OBJECT is a reference to one of String's supertypes, but points to an object at runtime that is not a String, it will be a ClassCastException.

Wrapper Class in Java

Java platform  provides primitive data types has a class dedicated to it. These are known as wrapper classes, because they "wrap" the primitive data type into an object of that class. Often, the wrapping is done by the compiler-if you use a primitive where an object is expected, the compiler boxes the primitive in its wrapper class for you. Similarly, if you use a number object when a primitive is expected, the compiler unboxes the object for you.So, there is anInteger class that holds an int variable, there is a Double class that holds a double variable, and so on.


Example for primitive data types and classes



Primitive type           Wrapper class Constructor Arguments

    byte                          Byte                       byte or String

    short                         Short                      short or String
    int                             Integer                    int or String
    long                          Long                      long or String
    float                          Float                      float, double or String

    double                      Double                   double or String

    char                         Character               char
    boolean                    Boolean                 boolean or String

Recover Mysqldump Got Errno 28 On Write

     While taking Mysqldump you may got error like Backup Failed in Mysqldump Got Errno 28 On Write.
     Because of inadequate disk space to store your output file. For that you have to free up some disk space.That's all now error willl gone and working fine

BufferReader

     BufferedReader reads text from a character-input stream, buffering characters so as to provide for the efficient reading of characters, arrays, and lines. It can also  read data from the files and console.It has two constructors

BufferedReader(Reader inputStream) 
BufferedReader(Reader inputStream, int bufSize)

     The first form creates a buffered character stream using a default buffer size. In the second, the size of the buffer is passed in bufSize.

     The most common Syntax for BufferedReader is

BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

     This line will create a new BufferedReader object, which reads from System.in (standard input). The InputStreamReader part is used to convert System.in (which is an InputStream) to a Reader object (which can be used by BufferedReader).

     After creating br, you can read input from the user:
String input = br.readLine(); 

     That will allow the user to type in anything and hit <Enter> button, and have what they typed in stored in input.

Ignore tables in MySQLdump

While taking mysqldump  some time error coming like databaseName.tableName crossed.meanwhile time you have to exclude that tables.And you don't want to include  some tables while taking mysqldump.


For that we can use    "--ignore-table=DbName.TableName" infront of  DbName in mysqldump command.see below dump command

mysqldump -ruserName -ppassWord  ----ignore-table=DbName.TableName DbName > DbName.sql

This command exclude which table you need to omit.

You can exclude multiple table also

mysqldump -ruserName -ppassWord --ignore-table=DbName.TableName1 --ignore-table=DbName.TableName2 > database.sql

Example:

mysqldump -rroot -proot  ----ignore-table=TEST.TEST_DATA TEST > TEST.sql