I am a new user of linux. I am using KNOPPIX and I would like to know how to shut down another computer(using redhat) through lan, is there anyone can help?

ssh to the server & use commands shutdown -h now or init 0

what if I want to set up a password so that I need to type in the password before shutdown?
thankyou very much

You'll need to type a password before you can login with ssh, or you can use ssh keys, which is even more secure. So a (root) password is required before you can shutdown the pc.

In fact I would like to know whether I can type in only one like command and remote shut down other's computer???
my boss need it!!!!urgent

If you setup ssh keys in the remote box for the root user then you can use a command like this:
Of course you must allow root to ssh (change sshd_config in the remote box accordingly)

Regards

Sorry, how should I input the ip address of th******e other computer?
since i saved the command , it still dun work

You must first create your pair of ssl keys in the local box (if they don't exist):Tranfer the file ~/.ssh/id_rsa.pub in the remote box and take a look under the root's home directory (usually /root). If there is a subdir named .ssh go in there and look for a file named authorized_keys. If it exists just copy the contents of id_rsa.pub in there. If not rename "id_rsa.pub" to "authorized_keys".
In the remote box you must enable sshd and edit it's config file (usually /etc/ssh/sshd_config). Find the line and change "no" to "yes". After this restart sshd and try the command I gave you. If you want to use IP, run:
Good luck