How to do Linux routing !basics

Linux routing basics

Most of the people doesn’t know that linux/*nix systems can be used as routers. Even there is a project called Linux routing and separate Linux OS for routing purpose alone, that’s the flexibility of Linux. In linux/*nix every work can be done in two ways.

That is one temporary way(after reboots these changes will not be there) and

the other is permanent way(after reboots too the changes will be there).

Creating routes in Linux : Basic Linux routing 

Add a route to a network

#route add -net network/mask gw default-gateway 

Example 

#route add -net 10.10.10.0/24 gw 192.168.0.1

Or

#route add 10.10.10.1 gw 192.168.0.1

Adding default gateway

#route add default gw default-gateway
Example 
#route add default gw 192.168.0.1 

Adding a route to specific host

#route add -host host-name gw default-gateway 

Example:

 #rotue add -host 2.34.5.6 gw 192.168.0.1Or

#route add 2.34.5.6 gw 192.168.0.1

Deleting route to a network

#route del -network network/subnet default-gateway

Example 

#route del -net 10.10.10.0/24 gw 192.168.0.1

Deleting default gateway

#route del default gw default-gatway

Example :

#route del default gw 192.168.0.1

Deleting specific host from routing table

#route del -host ip-add gw default-gateway
Example 
#route del -host 10.10.10.45 gw 192.168.0.1

Seeing routing table

#netstat -rn
#route -n 

Note : The old gate way will still remain and may need to be taken out for the system to function properly. Routes are made permanent in Red Hat Linux by adding routes to/etc/sysconfig/static-routes.

How to create User without password in Linux

Below mentioned command can create user without password in Linux using single command.

Note: having an account without password might be a security threat. I recommend to only enable the account when needed,

useradd -p "" (username)
Sample as below......
#useradd -p "" rahul 

Now you can trying login using rahul user system will not ask for password.

How to Recover Mysql root password

Recover Mysql root password

One of the very worst scenarios for a system administrator is when they forget a password for the root account. That is the same case when a Database admin does the same for the root account for Mysql Database. So to help here, these are the following steps which one can perform to recover the root password back for Mysql database.

Stop Mysql Server:

$ sudo /etc/init.d/mysql stop

Then, start the mysql server with skip-grant-tables options. –skip-grant-tables option will force the mysql process not to read the user table into memory, so that when you try to login to the Mysql server, it won’t ask for the password.

$ sudo mysqld_safe --skip-grant-tables  &

Now connect to mysql server using mysql client without giving any password

$ mysql -u root -p

Now setup the new password for the root user:

mysql> use mysql;
mysql> update user set password=PASSWORD("NEWPASSWORD") where user="root";
 mysql> flush privileges;
 mysql> Ctrl+D [to exit]

Now stop the mysql server

$ sudo /etc/init.d/mysql stop

Now start the mysql server normally, so that it could read the password information.

$ sudo /etc/init.d/mysql start

Disable Ctrl Alt Delete in Ubuntu

Disable Ctrl+Alt+Delete
First and foremost, anyone that has physical access to the keyboard can simply use the
Ctrl+Alt+Delete key combination to reboot the server without having to log on. Sure, someone could
simply unplug the power source, but you should still prevent the use of this key combination on a
production server.
This forces an attacker to take more drastic measures to reboot the server, and will
prevent accidental reboots at the same time.

• To disable the reboot action taken by pressing the Ctrl+Alt+Delete key combination, comment out
the following line in the file /etc/init/control-alt-delete.conf.

#exec shutdown -r now "Control-Alt-Delete pressed"

#sudo vi /etc/init/control-alt-delete.conf
# control-alt-delete - emergency keypress handling
#
# This task is run whenever the Control-Alt-Delete key combination is
# pressed, and performs a safe reboot of the machine.
description     "emergency keypress handling"
author          "Scott James Remnant <scott@netsplit.com>"
start on control-alt-delete
task
#exec shutdown -r now "Control-Alt-Delete pressed"

Package manager dpkg in Debian-based systems

dpkg is a package manager for Debian-based systems. It can install, remove, and build packages, but
unlike other package management systems, it cannot automatically download and install packages or
their dependencies. This section covers using dpkg to manage locally installed packages:

• To list all packages installed on the system, from a terminal prompt type:

dpkg -l

• Depending on the amount of packages on your system, this can generate a large amount of output.

Pipe the output through grep to see if a specific package is installed:

dpkg -l | grep apache2

Replace apache2 with any package name, part of a package name, or other regular expression.

• To list the files installed by a package, in this case the ufw package, enter:

dpkg -L ufw

• If you are not sure which package installed a file, dpkg -S may be able to tell you. For example:

 You can install a local .deb file by entering:

sudo dpkg -i zip_3.0-1_i386.deb

Change zip_3.0-4_i386.deb to the actual file name of the local .deb file you wish to install.

• Uninstalling a package can be accomplished by:

sudo dpkg -r zip

Uninstalling packages using dpkg, in most cases, is NOT recommended. It is better to use

a package manager that handles dependencies to ensure that the system is in a consistent

state. For example using

 dpkg -r zip

 will remove the zip package, but any packages that

depend on it will still be installed and may no longer function correctly.

For more dpkg options see the man page: man dpkg.

How to Chanage Jboss Admin Password

By default jboss admin password will be same as user name admin. 
but we need to  secure the JBOSS server in a production environment, and You can change it by editing file-

 Jboss/server/default/conf/props/jmx-console-users.properties. 

Simply change the password and save: 

# A sample users.properties file for use with the UsersRolesLoginModule
admin=Your Password

How to Release Cache Memory In Linux

To check uses of Cache Memory

free -m

rahul@rahul-laptop:~# free -m
             total       used       free     shared    buffers     cached
Mem:           992        898         94          0         14        460
-/+ buffers/cache:        604        388
Swap:         1011        132        879

To Release/ Free  Cache Memory 

rahul@rahul-laptop:~# sync, echo 3 > /proc/sys/vm/drop_caches 

Above command will free used cache memory
 to verify run again free -m

     OR 

rahul@rahul-laptop:~# sync && echo 1 > /proc/sys/vm/drop_caches