Using echo command on linux

To empty file 

 echo -n > filename

To insert text into file

 echo "hello" > filename 

Bind multiple ip address to NIC in Debian

First, back up your working interface to somewhere.

# cp /etc/network/interfaces /root/bak.interface

Then edit file

# vi /etc/network/interfaces

## This is how to bind multiple ip to NIC

auto eth0

auto eth0:0

auto eth0:1

iface eth0 inet static

address 192.168.20.31

netmask 255.255.255.0

gateway 192.168.20.1

iface eth0:0 inet static

address 192.168.20.32

netmask 255.255.255.0

gateway 192.168.20.1

iface eth0:1 inet static

address 192.168.20.33

netmask 255.255.255.0

gateway 192.168.20.1

##save and quit

##restart network service

How to add mysql user

To create a super user to local host

mysql> create user 'dunhill'@'localhost' identified by 'password';

mysql>grant all privileges on *.* to 'dunhill'@'localhost' with grant option;

To create a super user to any host

mysql> create user 'dunhill'@'%' identified by 'password';

mysql> grant all privileges on *.* to 'dunhill'@'%' with grant option;

To create a normal user with limited access

mysql> create user 'admin'@'localhost';

mysql> grant reload,process on *.* to 'admin'@'localhost';