Your own installed CIDR tables

When setting up networking, one of useful tool is the cidr tables, where you can refer the netmask and you can determine the cidr length for your netmask. Usually people will search the internet for network calculator or try to search for the cidr table. There is another easy way for you to have a cidr table installed in your computer and you can refer to it anytime you want using a single command. The package is perl-Net-IP. Install it using yum.

# yum install perl-Net-IP

After the installation finished, you can refer to the cidr table using the below command:

# iptab

There you go, a cidr table installed in your own computer for your own reference anytime. Have fun :-)

Sending message to users

To send message to a particular user, you have to know what is the user tty. You can do this by typing:

# w

This command is used to show who is logged on and what they are doing. The output of the above command is usually like below(Click to see the image clearly):



To send message to a specific user:

$ write username tty

Example, to send message to user user1:

$ write user1 pts/3

Write you messages, and then press Ctrl-d to exit 'write'

To send message to all connected user, use wall command:

$ wall

Type your message and Ctrl-d to exit 'wall'