Linux - NewbieThis Linux forum is for members that are new to Linux.
Just starting out and have a question?
If it is not in the man pages or the how-to's this is the place!
Welcome to LinuxQuestions.org, a friendly and active Linux Community.
You are currently viewing LQ as a guest. By joining our community you will have the ability to post topics, receive our newsletter, use the advanced search, subscribe to threads and access many other special features. Registration is quick, simple and absolutely free. Join our community today!
Note that registered members see fewer ads, and ContentLink is completely disabled once you log in.
If you have any problems with the registration process or your account login, please contact us. If you need to reset your password, click here.
Having a problem logging in? Please visit this page to clear all LQ-related cookies.
Introduction to Linux - A Hands on Guide
This guide was created as an overview of the Linux Operating System, geared toward new users as an exploration tour and getting started guide, with exercises at the end of each chapter.
For more advanced trainees it can be a desktop reference, and a collection of the base knowledge needed to proceed with system and network administration. This book contains many real life examples derived from the author's experience as a Linux system and network administrator, trainer and consultant. They hope these examples will help you to get a better understanding of the Linux system and that you feel encouraged to try out things on your own.
Click Here to receive this Complete Guide absolutely free.
Its Completely a new RHEL4U6 system.I dint do any change to the system.It was installed yesterday.All I find is whenever I ssh through any other machine I find "SOMEONE NASTY IS GOING ON YOUR MACHINE" and it says to delete /root/.ssh/known_hosts file.But when I delete that file,it allows me.After Sometime If I will login through any other machine,it prevents me saying the same error.Again,I delete the file..and it goes on..
The known_hosts file keeps a list of machines to which you have connected, and a cryptographic id of that machine. The point of the file is to make sure that when you re-connect to a machine which you have previously connected to, that it is the same machine.
What causes the message you see is that the remote machine's ID has changed. This can happen if the machine's identification keys are re-generated (e.g. you re-install the OS on the machine, or run the server key generation routine.
What it is trying to prevent is some attacker hijacking the machine's IP address and pretending to be that machine. An attacker might do this to get your password - if the attacker's machine has stolen the IP address of your machine, and you try to connect to it with a password, the attacker can steal your password.
If you are the owner/admin of the machine to which you are trying to connect, you should know if you have recently re-installed the OS, or re-generated the server keys. If you know you have done this, then it's fine to delete the known_hosts file. You will need to do this every time you re-generate the server keys or re-install the OS. The solution to the problem is simply not to regenerate the server keys. There is no reason to do it unless there is some known problem, such as the recent debian bug in ssh.
However, if you get this message at un-expected times, it is possible that someone is trying to steal your password.