Linux - GeneralThis Linux forum is for general Linux questions and discussion.
If it is Linux Related and doesn't seem to fit in any other forum then 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.
The words 'secure' and 'telnet' are seldom used in the same sentance unless its to say "using telnet you shaft any chance of setting up a secure server"
You could restrict access using a firewall to filter the telnet port but I'd advise you to install SSH. The problem with telnet is that it doesn't encrypt your password or the data it sends. Also IP addresses can be spoofed so I wouldn't rely on them for any kind of authentication/access control unless you have to. Check out http://www.openssh.org
This occurs on the linux server with SSHD running:
# iptables -P INPUT REJECT
# iptables -A INPUT -p tcp -s <the IP you want allowed> --dport 22 -j ACCEPT
Now I've had trouble when setting the default policy to REJECT, so I just do:
# iptables -A INPUT -p tcp -s <ditto> --dport 22 -j ACCEPT
# iptables -A INPUT -p tcp -j REJECT
Bear in mind that this will drop EVERY tcp packet except those designated at port 22(sshd) and from the specified IP address. If you want FTP access or any other service just mirror the above rules and change the dport to whichever port you want. Do this BEFORE the reject line if you use the 2nd method
if your email daemon is not popper, then check /etc/inetd.conf...look at pop3 section..look at the line,do you see the entry /usr/local/lib/popper popper , or /usr/local/lib/tcpd ipop3d ?If it is ipop3d, then in your allow file:
ipop3d : ALL
ipop3d : <ip addresses>
i hope i'm not confusing you...i dont know port and stuff,maybe i'll look it up !
But for some reason the server is acting funny about letting me log in with my one ip.
I was on site with the server this morning while my co-worker logged in off site. As I made different changes to deny and allow, he could get in if I commented out all entries in the deny file which is understandable. But when I uncommented ALL : ALL in deny my ip address entry did not work in the allow.
So I entered 199.178. to allow everything in that block which includes my ip and it let him in. But when I specified my one ip again it let him in. So I came back to the office 15 minutes later and now it wont let me in.
I am almost there and really apreciate everyones help.
when somebody is trying to ftp or telnet or whatever to your server, first your server will check allow file and see if that somebody is allowed. If it couldnt find a match there, then it would check deny file. Now you need to understand this: if you put in ALL : ALL in deny file, that somebody who doesnt have a match in allow file will NOT be able to get in. BUT, if you dont put in ALL : ALL, and instead, you specify a list of IP addresses and your server cant find a match for that somebody in that list too..guess what it will do?? It will let him/her in!Kind of confusing isnt it...that's why it is safer for us newbies to just put in ALL : ALL in deny file..so that anybody else aside from that allow file's list wont get in...( i hope i'm right..if i'm not,correct me
now,maybe you can work from there and figure out why your server is acting all funny with allow and deny...i'm off trying to figure out my biggest prob at the moment : subdomain dns server!wish me luck!